publicationDate,title,abstract,id
2011-08-31,Catalytic effect of the spinel ferrite nanocrystals on the growth of carbon nanotubes,"We prepared three ferrite nanocatalysts: (i) copper ferrite (CuFe2O4), (ii)
ferrite where cobalt was substituted by nickel (NixCo1-xFe2O4, with x= 0, 0.2,
0.4, 0.6), and (iii) ferrite where nickel was substituted by zinc
(ZnyNi1-yFe2O4 with y= 1, 0.7, 0.5, 0.3), by the sol-gel method. The X-ray
diffraction patterns show that the ferrite samples have been crystallized in
the cubic spinel structural phase. We obtained the grain size by FE-SEM images
in the range of 10-70 nm, and their magnetic properties by VSM. Next, carbon
nanotubes were grown on these nanocatalysts by the CCVD method. We show that
the catalytic effects of these nanocrystals on the carbon nanotube growth
depend on cation distributions in the octahedral and tetrahedral sites,
structural isotropy and catalytic power due to cations. Our study can have
applications in finding a suitable candidate of doped ferrite nanocrystals as
catalysts for carbon nanotube growth. More interestingly, the yield of the
fabrication of carbon nanotubes can be considered as an indirect tool to study
catalytic activity of ferrites.",1108.6256v1
2019-11-15,Exchange bias and training effect in an amorphous zinc ferrite/ nanocrystalline gallium ferrite bilayer thin film,"In this paper I report, exchange bias effect in a bilayer thin film of
amorphous zinc ferrite and nanocrystalline gallium ferrite. The amorphous zinc
ferrite layer was deposited at room temperature (Ts = RT) on top of a
nanocrystalline gallium ferrite thin film using a pulsed laser. This bilayer
film showed large exchange bias effect (He ~ 418 Oe at 2 K). The exchange bias
shift decreased exponentially as the temperature increased and disappeared for
T > 30 K. Along with the exchange bias shift the film also showed enhanced
magnetization in Field Cooled (FC) measurements as compared to the Zero Field
Cooled (ZFC) magnetization. The bilayer film also showed training effect at 2
K, which followed spin configurational relaxation model. The observed exchange
bias effect could be attributed to the pinning anisotropy of the spin glass
amorphous zinc ferrite layer pinned at the interface of gallium ferrite.",1911.06493v1
2004-01-29,Review on Giant Magnetoelectric effects in Oxide ferromagnetic/ferroelectric Layered Structures,"The synthesis of layered ferrite-lead titanate zirconate (PZT) and lanthanum
nanganite-PZT and the observation of giant magneto-electric interactions are
discussed. The ferrites used in our studies included pure and Zn substituted
cobalt-, nickel- and lithium ferrites. Ferromagnetic manganites used included
both calcium and strontium substituted systems. The samples were prepared from
10-40 mm thick films obtained by tape-casting. Our studies showed strong ME
coupling in manganite-PZT and cobalt zinc ferrite-PZT, and a giant ME effect in
nickel zinc ferrite-PZT. We found evidence for Zn assisted enhancement in ME
coefficients that were attributed to low anisotropy and high permeability that
resulted in favorable magneto-mechanical coupling in the composites.",0401607v1
2008-07-27,Magnetic-dipolar and electromagnetic vortices in quasi-2D ferrite disks,"Magnetic-dipolar-mode (MDM) oscillations in a quasi-2D ferrite disk show
unique dynamical symmetry properties resulting in appearance of topologically
distinct structures. Based on the magnetostatic (MS) spectral problem
solutions, in this paper we give an evidence for eigen MS power-flow-density
vortices in a ferrite disk. Due to these circular eigen power flows, the MDMs
are characterized by MS energy eigen states. It becomes evident that the reason
of stability of the vortex configurations in saturated ferrite samples is
completely different from the nature of stability in magnetically soft
cylindrical dots. We found a clear correspondence between analytically derived
MDM vortex states and numerically modeled electromagnetic vortices in quasi-2D
ferrite disks.",0807.4281v1
2004-08-31,Handedness of magnetic-dipolar modes in ferrite disks,"For magnetic-dipolar modes in a ferrite, components of the magnetic flux
density in a helical coordinate system are dependent on both an orientation of
a gyration vector and a sign of a pitch. It gives four types of helical
harmonics for magnetostatic-potential wave functions in a ferrite disk. Because
of the reflection symmetry breaking, coupling between certain types of helical
harmonics takes place in the reflection points. The reflection feature leads to
exhibition of two types of resonances: the ""right"" and ""left"" resonances. These
resonances become coupled for a ferrite disk placed in a homogeneous tangential
RF magnetic field. One also observes such resonance coupling for a ferrite disk
with a symmetrically oriented linear surface electrode, when this ferrite
particle is placed in a homogeneous tangential RF electric field. In a
cylindrical coordinate system handedness of magnetic-dipolar modes in a ferrite
disk is described by spinor wave functions.",0408682v2
2010-06-01,Magnetic and humidity sensing properties of nanostructured Cu[x]Co[1-x]Fe2O4 synthesized by auto combustion technique,"Magnetic nanomaterials (23-43 nm) of Cu$_x$Co$_{1-x}$Fe$_2$O$_4$\ (x = 0.0,
0.5 and 1.0) were synthesized by auto combustion method. The crystallite sizes
of these materials were calculated from X-ray diffraction peaks. The band
observed in Fourier transform infrared spectrum near 575 cm$^{-1}$ in these
samples confirm the presence of ferrite phase. Conductivity measurement shows
the thermal hysteresis and demonstrates the knee points at 475$^o$C, 525$^o$C
and 500$^o$C for copper ferrite, cobalt ferrite and copper-cobalt mixed ferrite
respectively. The hystersis M-H loops for these materials were traced using the
Vibrating Sample Magnetometer (VSM) and indicate a significant increase in the
saturation magnetization (M$_s$) and remanence (M$_r$) due to the substitution
of Cu$^{2+}$ ions in cobalt ferrite, while the intrinsic coercivity (H$_c$) was
decreasing. Among these ferrites, copper ferrite exhibits highest sensitivity
for humidity.",1006.0083v1
2012-09-20,Nucleating Acicular Ferrite with Galaxite (Al2O3MnO) and Manganese Oxide (MnO2) in FeMnAlC steels,"Effectiveness of galaxite (Al2O3MnO) and manganese oxide (MnO2) in nucleating
acicular ferrite was demonstrated in a steel with composition of
Fe-13.92Mn-4.53Al-1.28Si-0.11C. The hot rolled and quenched steel had a duplex
microstructure of delta-ferrite and partially transformed austenite. Thermal
treatments were used to manipulate the concentration and type of oxides and the
ferrite plate density was found to correlate with inclusions of low misfit.
Both bainitic and acicular ferrite were observed and the prior austenite had a
grain diameter of 16.5 micrometers. Upon tensile testing the retained austenite
transformed to alpha-martensite. Ultimate tensile strength and elongation were
970 MPa and 40 percent. The yield strength was found to be dependent on the
ferrite plate size, which varied linearly with the strength of the austenite.
Ductility decreased as the strength disparity between delta-ferrite and
deformation-induced alpha-martensite increased.",1209.4546v1
2021-04-23,"Plasticity, localization, and damage in ferritic-pearlitic steel studied by nanoscale digital image correlation","The evolution of deformation from plasticity to localization to damage is
investigated in ferritic-pearlitic steel through nanometer-resolution
microstructure-correlated SEM-DIC (u-DIC) strain mapping, enabled through
highly accurate microstructure-to-strain alignment. We reveal the key
plasticity mechanisms in ferrite and pearlite as well as their evolution into
localization and damage and their relation to the microstructural arrangement.
Notably, two contrasting mechanisms were identified that control whether damage
initiation in pearlite occurs and, through connection of localization hotspots
in ferrite grains, potentially results in macroscale fracture: (i) cracking of
pearlite bridges with relatively clean lamellar structure by brittle fracture
of cementite lamellae due to build-up of strain concentrations in nearby
ferrite, versus (ii) large plasticity without damage in pearlite bridges with a
more ""open"", chaotic pearlite morphology, which enables plastic percolation
paths in the interlamellar ferrite channels. Based on these insights,
recommendations for damage resistant ferritic-pearlitic steels are proposed.",2104.11817v2
2022-05-13,Ferrite: A Judgmental Embedding of Session Types in Rust,"\emph{Session types} have proved viable in expressing and verifying the
protocols of message-passing systems. While message passing is a dominant
concurrency paradigm in practice, real world software is written without
session types. A limitation of existing session type libraries in mainstream
languages is their restriction to linear session types, precluding application
scenarios that demand sharing and thus aliasing of channel references.
  This paper introduces Ferrite, a shallow embedding of session types in Rust
that supports both \emph{linear} and \emph{shared} sessions. The formal
foundation of Ferrite constitutes the shared session type calculus $\sills$,
which Ferrite encodes via a novel \emph{judgmental embedding} technique. The
fulcrum of the embedding is the notion of a typing judgment that allows
reasoning about shared and linear resources to type a session. Typing rules are
then encoded as functions over judgments, with a valid typing derivation
manifesting as a well-typed Rust program. This Rust program generated by
Ferrite serves as a \emph{certificate}, ensuring that the application will
proceed according to the protocol defined by the session type. The paper
details the features and implementation of Ferrite and includes a case study on
implementing Servo's canvas component in Ferrite.",2205.06921v2
2016-06-08,Magnetoelectric effect in layered ferrite/PZT composites. Study of the demagnetizing effect on the magnetoelectric behavior,"We report the use of high magnetomechanical coupling ferrites in
magnetoelectric (ME) layered composites. Bilayer samples combining $(Ni_{0.973}
Co_{0.027})_{1-x} Zn_x Fe_2 O_4$ ferrites ($x = 0-0.5$) synthesized by non
conventional reactive Spark Plasma Sintering and commercial lead zirconate
titanate (PZT) were characterized in term of ME voltage coefficients measured
at sub-resonant frequency. Strong ME effects are obtained and we show that an
annealing at 1000$^\circ$C and a quenching in air improve the piezomagnetic
behavior of Zn-rich compositions. A theoretical model that predicts the ME
behavior was developed, focusing our work on the demagnetizing effects in the
transversal mode as well as the longitudinal mode. The model shows that: (i)
high ME coefficients are obtained when ferrites with high magnetomechanical
coupling are used in bilayer ME composites, (ii) the ME behavior in transversal
and longitudinal modes is quite similar, and differences in the shapes of the
ME curves are mainly due the demagnetizing effects, (iii) in the transversal
mode, the magnetic field penetration depends on the ferrite layer thickness and
the ME coefficient is affected accordingly. The two later points are confirmed
by measurements on ME samples and calculations. Performances of the ME
composites made with high magnetomechanical coupling ferrites are compared to
those obtained using Terfenol-D materials in the same conditions of size,
shape, and volume ratio. It appears that a ferrite with an optimized
composition has performances comparable to those obtained with Terfenol-D
material. Nevertheless, the fabrication processes of ferrites are quite
simpler. Finally, a ferrite/PZT based ME composite was used as a current
sensor.",1606.02473v1
2006-02-19,Low sintering temperature of Mg-Cu-Zn ferrites prepared by the citrate precursor method,"Mg-Cu-Zn ferrite was prepared through a wet synthetic method by a
self-combustion reaction directly from a citrate precursor. The as-synthesized
powders were sintered at for only 2h. XRD patterns and FTIR spectra confirm the
formation of single phase Mg-Cu-Zn ferrite after combustion. To the best of our
knowledge, this is the first time that Mg-Cu-Zn ferrite is sintered at such low
temperature. The sintering process increased the crystallinity of the solid and
the domain sizes.",0602129v1
2007-04-19,Classical Heisenberg Hamiltonian Solution of Oriented Spinel Ferrimagnetic Thin Films,"The classical Heisenberg Hamiltonian was solved for oriented spinel thin and
thick cubic ferrites. The dipole matrix of complicated cubic cell could be
simplified into the form of dipole Matrix of simple cubic cells. This study was
confined only to the highly oriented thin films of ferrite. The variation of
total energy of Nickel ferrite thin films with angle and number of layers was
investigated. Also the change of energy with stress induced anisotropy for
Nickel ferrite films with N=5 and 1000 has been studied. Films with the
magnetic moments ratio 1.86 can be easily oriented in 90 direction when N is
greater than 400.",0704.2456v1
2016-07-08,Third Order Perturbed Energy of Cobalt Ferrite Thick Films,"Magnetic properties and easy axis orientation of cobalt ferrite films with
applied magnetic field and number of layers were studied. According to our
theoretical studies explained in this manuscript, the magnetically easy and
hard directions of cobalt ferrite films solely depend on in plane and out of
plane magnetic fields. According to 3-D and 2-D plots, there are many easy and
hard directions at one particular value of in plane or out of plane magnetic
field. The magnetic properties were investigated for cobalt ferrite films with
thickness up to 10,000 unit cells. The total magnetic energy was calculated for
a unit spin of cobalt.",1607.02323v1
2012-01-05,Ferrite cavities,"Ferrite cavities are used in synchrotrons and storage rings if the maximum RF
frequency is in the order of a few MHz. We present a simple model for
describing ferrite cavities. The most important parameters are defined, and the
material properties are discussed. Several practical aspects are summarized,
and the GSI SIS18 ferrite cavity is presented as an example.",1201.1154v1
2023-01-03,Crystal Nucleation Modeling of Solvent Molecules Influence on Radius and Morphology of Nano Copper Ferrite Particles,"Nanometer copper ferrite, as a kind of nanometer particle with catalytic
activity, and its photothermal and magnetothermal effects as ferrite, can be
widely used in different fields. It is a general way to obtain the nano effect
of the target by controlling the particle size. In this paper, the
crystallization process of hydrothermal/solvothermal synthesis was analyzed,
and the nucleation model was established to simulate the effects of solvent,
reaction temperature and cooling time on the particle size of copper ferrite
nanoparticles. Through Monte Carlo method and energy function, the ratio of
nano particle agglomeration was established, and the influence of different
reaction conditions on it was discussed.",2301.00905v1
2018-03-25,Analytical modeling of demagnetizing effect in magnetoelectric ferrite/PZT/ferrite trilayers taking into account a mechanical coupling,"In this paper, we investigate the demagnetizing effect in ferrite/PZT/ferrite
magnetoelectric (ME) trilayer composites consisting of commercial PZT discs
bonded by epoxy layers to Ni-Co-Zn ferrite discs made by a reactive Spark
Plasma Sintering (SPS) technique. ME voltage coefficients (transversal mode)
were measured on ferrite/PZT/ferrite trilayer ME samples with different
thicknesses or phase volume ratio in order to highlight the influence of the
magnetic field penetration governed by these geometrical parameters.
Experimental ME coefficients and voltages were compared to analytical
calculations using a quasi-static model. Theoretical demagnetizing factors of
two magnetic discs that interact together in parallel magnetic structures were
derived from an analytical calculation based on a superposition method. These
factors were introduced in ME voltage calculations which take account of the
demagnetizing effect. To fit the experimental results, a mechanical coupling
factor was also introduced in the theoretical formula. This reflects the
differential strain that exists in the ferrite and PZT layers due to shear
effects near the edge of the ME samples and within the bonding epoxy layers.
From this study, an optimization in magnitude of the ME voltage is obtained.
Lastly, an analytical calculation of demagnetizing effect was conducted for
layered ME composites containing higher numbers of alternated layers (). The
advantage of such a structure is then discussed.",1803.09315v1
2022-02-16,Unusual ferrimagnetic ground state in rhenium ferrite,"Through comprehensive density functional calculations, we predict the
stability of a rhenium-based ferrite",2202.08115v1
2016-06-08,A method to decrease the harmonic distortion in Mn-Zn ferrite/PZT and Ni-Zn ferrite/PZT layered composite rings exhibiting high magnetoelectric effects,"We have investigated the magnetoelectric (ME) effect in layered composite
rings subjected to circumferential AC magnetic fields and DC magnetic fields in
radial, axial or circumferential directions. Bilayer samples were obtained
combining different grades of commercial Mn-Zn ferrites or Ni-Zn ferrites with
commercial lead zirconate titanate (PZT). Mn-Zn ferrites with low
magnetostriction saturation () and low magneto-crystalline anisotropy constants
show high ME capabilities when associated with PZT in ring structures. In
certain conditions, these ME effects are higher than those obtained with
Terfenol-D/PZT composites in the same layered ring structure. Magnetostrictive
and mechanical characterizations have given results that explain these high ME
performances. Nevertheless, Mn-Zn ferrite/PZT composites exhibit voltages
responses with low linearity especially at high signal level. Based on the
particular structure of the ME device, a method to decrease the nonlinear
harmonic distortion of the ME voltages is proposed. Harmonic distortion
analysis of ME voltages measured in different configurations allows us to
explain the phenomenon.",1606.02469v1
2013-09-11,Fano resonances of microwave structures with embedded magneto-dipolar quantum dots,"Long range dipole-dipole correlation in a ferromagnetic sample can be treated
in terms of collective excitations of the system as a whole. Ferrite samples
with linear dimensions smaller than the dephasing length, but still much larger
than the exchange-interaction scales are mesoscopic structures. Recently, it
was shown that mesoscopic quasi-2D ferrite disks, distinguishing by
multiresonance magneto-dipolar-mode (MDM) spectra, demonstrate unique
properties of artificial atomic structures: energy eigenstates, eigen
power-flow vortices and eigen helicity parameters. Because of these properties,
MDMs in a ferrite disk enable the confinement of microwave radiation to
subwavelength scales. In microwave structures with embedded MDM ferrite
samples, one can observe quantized fields with topologically distinctive
characteristics. The use of a quasi-2D ferrite-disk scatterer with internal MDM
resonance spectra along the channel propagation direction could change the
transmission dramatically. In this paper, we show that interaction of the MDM
ferrite particle with its environment has a deep analogy with the
Fano-resonance interference observed in natural and artificial atomic
structures. We characterize the observed effect as Fano-resonance interference
in MDM quantum dots.",1309.2792v1
2020-09-28,Ferrite: A Judgmental Embedding of Session Types in Rust,"This paper introduces Ferrite, a shallow embedding of session types in Rust.
In contrast to existing session type libraries and embeddings for mainstream
languages, Ferrite not only supports linear session types but also shared
session types. Shared session types allow sharing (aliasing) of channels while
preserving session fidelity (preservation) using type modalities for acquiring
and releasing sessions. Ferrite adopts a propositions as types approach and
encodes typing derivations as Rust functions, with the proof of successful
type-checking manifesting as a Rust program. We provide an evaluation of
Ferrite using Servo as a practical example, and demonstrate how safe
communication can be achieved in the canvas component using Ferrite.",2009.13619v6
2023-04-20,Control of conductivity in Fe-rich cobalt-ferrite thin films with perpendicular magnetic anisotropy,"We fabricated two types of cobalt-ferrite (001) thin films, insulative
Fe-rich cobalt-ferrite CoxFe3-xO4+{\delta} (I-CFO) and conductive Fe-rich
cobalt-ferrite CoyFe3-yO4 (C-CFO), with perpendicular magnetic anisotropy (PMA)
on MgO (001) substrates. Although the stoichiometric cobalt-ferrite is known as
an insulating material, it is found that the conductivity of Fe-rich
cobalt-ferrites can be controlled by changing the source materials and
deposition conditions in the pulsed laser deposition technique. The I-CFO and
C-CFO films exhibit PMA through the in-plane lattice distortion. We
investigated the Fe-ion-specific valence states in both I-CFO and C-CFO films
by M\""ossbauer spectroscopy and X-ray magnetic circular dichroism, and found
that the difference in conductivity corresponds to the abundance ratio of Fe2+
state at the octahedral B-site (Oh) in the inverse spinel structure.
Furthermore, first-principles calculations reproduce the changes in the density
of states at the Fermi level depending on the cation vacancies at the B-site,
which explains the difference in the conductivity between I-CFO and C-CFO.",2304.10048v1
2023-09-24,Greener processing of SrFe$_{12}$O$_{19}$ ceramic permanent magnets by two-step sintering,"With an annual production amounting to 800 kilotons, ferrite magnets
constitute the largest family of permanent magnets in volume, a demand that
will only increase as a consequence of the rare-earth crisis. With the global
goal of building a climate-resilient future, strategies towards a greener
manufacturing of ferrite magnets are of great interest. A new ceramic
processing route for obtaining dense Sr-ferrite sintered magnets is presented
here. Instead of the usual sintering process employed nowadays in ferrite
magnet manufacturing that demands long dwell times, a shorter two-step
sintering is designed to densify the ferrite ceramics. As a result of these
processes, dense SrFe$_{12}$O$_{19}$ ceramic magnets with properties comparable
to state-of-the-art ferrite magnets are obtained. In particular, the
SrFe$_{12}$O$_{19}$ magnet containing 0.2% PVA and 0.6% wt SiO$_2$ reaches a
coercivity of 164 kA/m along with a 93% relative density. A reduction of 31% in
energy consumption is achieved in the thermal treatment with respect to
conventional sintering, which could lead to energy savings for the industry of
the order of 7.109 kWh per year.",2309.15860v1
2004-01-30,Magnetoelectric Effects in Ferromagnetic/Piezoelectric Multilayer Composites,"The observation of strong magnetoelectric effects is reported in thick film
bilayers and multilayers of ferrite-lead titanate zirconate (PZT) and lanthanum
nanganite-PZT. The ferrites used in our studies included pure and zinc
substituted cobalt-, nickel- and lithium ferrites. Samples were prepared by
sintering 10-40 mm thick films obtained by tape-casting. Measurements of ME
voltage coefficients at 10-1000 Hz indicated a giant ME effect in nickel
ferrite-PZT, but a relatively weak coupling in other ferrite-PZT and
manganite-PZT systems. Multilayers prepared by hot pressing was found to show a
higher ME coefficient than sintered samples. Evidence was found for enhancement
in ME coefficients when Zn was substituted in ferrites. The Zn-assisted
increase was attributed to low anisotropy and high permeability that resulted
in favorable magneto-mechanical coupling in the composites. We analyzed the
data in terms of our recent comprehensive theory that takes into account actual
interface conditions by introducing an interface coupling parameter.
Theoretical longitudinal and transverse ME voltage coefficients for unclamped
and clamped samples are in general agreement with data. From the analysis we
inferred excellent interface coupling for nickel zinc ferrite-PZT and weak
coupling for other layered systems.",0401641v1
2013-02-19,On the evolution of the non exchange spring behaviour to the exchange spring behaviour: A First Order Reversal Curve Analysis,"The magnetization behaviour of the soft Cobalt Ferrite-hard Strontium Ferrite
nanocomposite is tuned from the non exchange spring nature to the exchange
spring nature, by controlling the particle size of the soft Cobalt Ferrite in
the Cobalt Ferrite: Strontium Ferrite (1:8) nanocomposite. The relative
strength of the interaction governing the magnetization process in the
nanocomposites is investigated using Henkel plot and First Order Reversal Curve
(FORC) method. The FORC method has been utilized to understand the
magnetization reversal behaviour as well as the extent of the irreversible
magnetization present in both the nanocomposites having smaller and larger
particle size of the Cobalt Ferrite. The magnetization process is primarily
controlled by the domain wall movement in the nanocomposites. Using the FORC
distribution in the (Ha, Hb) co-ordinate, the onset of the nucleation field,
invasion of the domain wall from the soft to the hard phase, domain wall
annihilation and the presence of the reversible magnetization with the applied
reversal field for both the nanocomposites has been investigated. It has been
found that for the composite having lower particle size of the soft phase shows
a single switching behaviour corresponding to the coherent reversal of the both
soft and hard phases. However, the composite having higher Cobalt Ferrite
particle size shows two peak behaviour in the FORC distribution resembling
individual switching of the soft and hard phases. The FORC distribution in (Hu,
Hc) co-ordinate and the Henkel measurement confirms the dominant exchange
interaction in the nanocomposites exhibiting exchange spring behaviour where as
the occurrence of both the dipolar and exchange interaction is substantiated
for the non exchange coupled nanocomposite.",1302.4602v1
2010-05-18,Micromagnetic simulations of spinel ferrite particles,"This paper presents the results of simulations of the magnetization field
{\it ac} response (at $2$ to $12$ GHz) of various submicron ferrite particles
(cylindrical dots). The ferrites in the present simulations have the spinel
structure, expressed here by M$_{1-n}$Zn$_{n}$Fe$_2$O$_4$ (where M stands for a
divalent metal), and the parameters chosen were the following: (a) for $n=0$: M
= \{ Fe, Mn, Co, Ni, Mg, Cu \}; (b) for $n=0.1$: M = \{ Fe, Mg \} (mixed
ferrites). These runs represent full 3D micromagnetic (one-particle) ferrite
simulations. We find evidences of confined spin waves in all simulations, as
well as a complex behavior nearby the main resonance peak in the case of the M
= \{ Mg, Cu \} ferrites. A comparison of the $n=0$ and $n=0.1$ cases for fixed
M reveals a significant change in the spectra in M = Mg ferrites, but only a
minor change in the M = Fe case. An additional larger scale simulation of a $3$
by $3$ particle array was performed using similar conditions of the Fe$_3$O$_4$
(magnetite; $n=0$, M = Fe) one-particle simulation. We find that the main
resonance peak of the Fe$_3$O$_4$ one-particle simulation is disfigured in the
corresponding 3 by 3 particle simulation, indicating the extent to which
dipolar interactions are able to affect the main resonance peak in that
magnetic compound.",1005.3169v1
2003-07-13,"Structural and magnetoelectric properties of MFe2O4-PZT (M=Ni,Co) and (La)x(Ca,Sr)1-x - PZT multilayers","Thick film layered magnetoelectric composites consisting of ferromagnetic and
ferroelectric phases have been synthesized with nickel ferrite (NFO), cobalt
ferrite (CFO), La0.7Sr0.3MnO3 (LSMO), or La0.7Ca0.3MnO3 (LCMO) and lead
zirconate titanate (PZT). Structural, magnetic and ferromagnetic resonance
characterization shows evidence for defect free ferrites, but deterioration of
manganite parameters. The resistivity and dielectric constants are smaller than
expected values. The magnetoelectric effect (ME) is stronger in ferrite-PZT
than in manganite-PZT. The ME voltage coefficient aE at room temperature is the
highest in NFO-PZT and the smallest for LCMO-PZT. The transverse ME effect is
an order of magnitude stronger than the longitudinal effect. The magnitude of
aE correlates well with magnetic permeability for the ferrites.",0307309v1
2004-09-22,Interaction of magnetic-dipolar modes with microwave-cavity electromagnetic fields,"We discuss the problem of magnetic-dipolar oscillations combined with
microwave resonators. The energy density of magnetic-dipolar or magnetostatic
(MS) oscillations in ferrite resonators is not the electromagnetic-wave density
of the energy and not the exchange energy density as well. This fact reveals
very special behaviors of the geometrical effects. Compared to other
geometries, thin-film ferrite disk resonators exhibit very unique interactions
of MS oscillations with the cavity electromagnetic fields. MS modes in a flat
ferrite disk are characterized by a complete discrete spectrum of energy
levels. The staircase demagnetization energy in thin-film ferrite disks may
appear as noticeable resonant absorption of electromagnetic radiation. Our
experiments show how the environment may cause decoherence for magnetic
oscillations. Another noticeable fact is experimental evidence for
eigen-electric-moment oscillations in a ferrite disk resonator.",0409583v2
2011-03-25,Temperature dependence of core loss in cobalt substituted Ni-Zn-Cu ferrites,"The temperature dependence of core loss in cobalt substituted Ni-Zn-Cu
ferrites was investigated. Co2+ ions are known to lead to a compensation of the
magneto-crystalline anisotropy in Ni-Zn ferrites, at a temperature depending on
the cobalt content and the Ni/Zn ratio. We observed similar behaviour in
Ni-Zn-Cu and it was found that the core loss goes through a minimum around this
magneto-crystalline anisotropy compensation. Moreover, the anisotropy induced
by the cobalt allowed a strong decrease of core loss, a ferrite having a core
loss of 350 mW/cm3 at 80 ^\circ C was then developed (measured at 1.5 MHz and
25 mT). This result represents an improvement of a factor 4 compared to the
state of art Ni-Zn ferrites.",1103.5021v1
2011-05-30,Dependence of microwave absorption properties on ferrite volume fraction in MnZn ferrite/rubber radar absorbing materials,"We report the analysis of measurements of the complex magnetic permeability
($\mu_r$) and dielectric permittivity ($\epsilon_r$) spectra of a rubber radar
absorbing material (RAM) with various MnZn ferrite volume fractions. The
transmission/reflection measurements were carried out in a vector network
analyzer. Optimum conditions for the maximum microwave absorption were
determined by substituting the complex permeability and permittivity in the
impedance matching equation. Both the MnZn ferrite content and the RAM
thickness effects on the microwave absorption properties, in the frequency
range of 2 to 18 GHz, were evaluated. The results show that the complex
permeability and permittivity spectra of the RAM increase directly with the
ferrite volume fraction. Reflection loss calculations by the impedance matching
degree (reflection coefficient) show the dependence of this parameter on both
thickness and composition of RAM.",1105.5969v1
2015-10-20,Reflecting (on) the Nucleation Curve: Negative Surface Energy Stabilizes Nickel Ferrite Nano-Particles in Nuclear Reactor Coolant,"We used a thermodynamics-informed first principles scheme, to calculate the
temperature-dependent surface energies of nickel oxide (NiO) and nickel ferrite
(NiFe2O4), two compounds that are known to deposit on the fuel rods in nuclear
pressurized water reactors (PWR). These calculations predict a negative surface
free energy for nickel ferrite when formed from ions in solution under PWR
conditions of temperature, pressure and species concentration. Under these
conditions the thermodynamics of bulk nickel ferrite yields a positive change
in free energy for formation of the solid from dissolved ions. These results
and their analysis in terms of classical nucleation theory have suggested a new
fundamental relation - the reflected nucleation curve - that reveals a
previously unrecognized aspect of the theory of phase stability. These
calculations also suggest the presence of stable octahedral nickel ferrite
clusters in PWR coolant that would not be observed in the coolant outside of
service conditions, and that are not removed by the combination of filtration
and capture of solvated ions currently used to purify the PWR coolant.",1510.05901v1
2016-06-27,Structural and electrical properties of Sn substituted double sintering derived Ni-Zn ferrite,"The Sn substituted Ni-Zn ferrites were synthesized by the standard double
sintering technique using nano powders of nickel oxide (NiO), zinc oxide (ZnO),
iron oxide (Fe2O3) and tin oxide (SnO2). The structural and electrical
properties have been investigated by the X-ray diffraction, scanning electron
microscopy, DC resistivity and dielectric measurements. Extra intermediate
phase has been detected along with the inverse cubic spinel phase of Ni-Zn
ferrite. Enhancement of grain size is observed in Sn substituted Ni-Zn
ferrites. DC resistivity as a function of temperature has been investigated by
two probe method. The DC resistivity was found to decrease whereas the
dielectric constants increase with increasing Sn content in Ni-Zn ferrites. The
dielectric constant of the as prepared samples is high enough to use these
materials in miniaturized memory devices based capacitive components or energy
storage principles.",1606.08118v1
2016-09-27,A Noninvasive Magnetic Stimulator Utilizing Secondary Ferrite Cores and Resonant Structures for Field Enhancement,"In this paper, secondary ferrite cores and resonant structures have been used
for field enhancement. The tissue was placed between the double square source
coil and the secondary ferrite core. Resonant coils were added which aided in
modulating the electric field in the tissue. The field distribution in the
tissue was measured using electromagnetic simulations and ex-vivo measurements
with tissue. Calculations involve the use of finite element analysis (Ansoft
HFSS) to represent the electrical properties of the physical structure. The
setup was compared to a conventional design in which the secondary ferrite
cores were absent. It was found that the induced electric field could be
increased by 122%, when ferrite cores were placed below the tissue at 450 kHz
source frequency. The induced electric field was found to be localized in the
tissue, verified using ex-vivo experiments. This preliminary study maybe
further extended to establish the verified proposed concept with different
complicated body parts modelled using the software and in-vivo experiments as
required to obtain the desired induced field.",1609.08333v1
2020-11-30,Significant enhancement of magnetic shielding effect by using the composite metamaterial composed of mu-near-zero media and ferrite,"The magnetic shield plays an important role in magnetic near-field control.
However, the requirements of efficient, ultrathin, lightweight and cheap are
still the challenges. Here, we firstly propose a composite metamaterial in
which the mu-near-zero media is covered with a ferrite slab. We verify that
this structure can enhance the shielding effectiveness in a small area.
Furthermore, we optimize the magnetic path by changing the bulk ferrite slab
into a patterned slab. In this way, significant shielding effectiveness
enhancement can be achieved in a large area. Experimental results show that the
maximum shielding effectiveness (SE) of the composite metamaterial with a
patterned ferrite is 20.56 dB, which is nearly 19 dB higher than that of a
single ferrite slab with the same thickness of the composite metamaterial. The
results on the composite metamaterial would be very useful in the applications
involving magnetic shielding.",2012.07524v1
2019-01-30,Tuning the Magnetic Ordering Temperature of Hexagonal Ferrites by Structural Distortion Control,"To tune the magnetic properties of hexagonal ferrites, a family of
magnetoelectric multiferroic materials, by atomic-scale structural engineering,
we studied the effect of structural distortion on the magnetic ordering
temperature (TN). Using the symmetry analysis, we show that unlike most
antiferromagnetic rare-earth transition-metal perovskites, a larger structural
distortion leads to a higher TN in hexagonal ferrites and manganites, because
the K3 structural distortion induces the three-dimensional magnetic ordering,
which is forbidden in the undistorted structure by symmetry. We also revealed a
near-linear relation between TN and the tolerance factor and a power-law
relation between TN and the K3 distortion amplitude. Following the analysis, a
record-high TN (185 K) among hexagonal ferrites was predicted in hexagonal
ScFeO3 and experimentally verified in epitaxially stabilized films. These
results add to the paradigm of spin-lattice coupling in antiferromagnetic
oxides and suggests further tunability of hexagonal ferrites if more lattice
distortion can be achieved.",1901.11118v1
2019-08-23,Damping enhancement in coherent ferrite/insulating-paramagnet bilayers,"High-quality epitaxial ferrites, such as low-damping MgAl-ferrite (MAFO), are
promising nanoscale building blocks for all-oxide heterostructures driven by
pure spin current. However, the impact of oxide interfaces on spin dynamics in
such heterostructures remains an open question. Here, we investigate the spin
dynamics and chemical and magnetic depth profiles of 15-nm-thick MAFO
coherently interfaced with an isostructural $\approx$1-8-nm-thick overlayer of
paramagnetic CoCr$_2$O$_4$ (CCO) as an all-oxide model system. Compared to MAFO
without an overlayer, effective Gilbert damping in MAFO/CCO is enhanced by a
factor of $>$3, irrespective of the CCO overlayer thickness. We attribute this
damping enhancement to spin scattering at the $\sim$1-nm-thick chemically
disordered layer at the MAFO/CCO interface, rather than spin pumping or
proximity-induced magnetism. Our results indicate that damping in ferrite-based
heterostructures is strongly influenced by interfacial chemical disorder, even
if the thickness of the disordered layer is a small fraction of the ferrite
thickness.",1908.08629v2
2003-03-10,Energy Spectra of Magnetostatic Oscillations in Ferrite Disk Resonators,"Ferromagnetic resonators with short-wavelength, so-called magnetostatic (MS),
oscillations can be considered in microwaves as point (with respect to the
external electromagnetic fields) particles. It was shown recently [E. O.
Kamenetskii, Phys. Rev. E, 63, 066612 (2001)] that MS oscillations in a small
ferrite disk resonator can be characterized by a discrete spectrum of energy
levels. This fact allows analyzing the MS oscillations similarly to quantum
mechanical problems. In this paper we give the results of energy spectrum
calculations for MS oscillations in a ferrite disk resonator.",0303164v2
2004-04-03,Electromagnetic analog of Rashba spin-orbit interaction in wave guides filled with ferrite,"We consider infinitely long electromagnetic wave guide filled with a ferrite.
The wave guide has arbitrary but constant cross-section $. We show that Maxwell
equations are equivalent to the Schr\""odinger equation for single electron in
the two-dimensional quantum dot of the form D with account of the Rashba
spin-orbit interaction. The spin-orbit constant is determining by components of
magnetic permeability of the ferrite. The upper component of electron spinor
function corresponds to the z-th component electric field, while the down
component $\chi$ related to the z-th component of magnetic field by relation
(30).",0404072v1
2007-02-02,Induced Time-Reversal Symmetry Breaking Observed in Microwave Billiards,"Using reciprocity, we investigate the breaking of time-reversal (T) symmetry
due to a ferrite embedded in a flat microwave billiard. Transmission spectra of
isolated single resonances are not sensitive to T-violation whereas those of
pairs of nearly degenerate resonances do depend on the direction of time. For
their theoretical description a scattering matrix model from nuclear physics is
used. The T-violating matrix elements of the effective Hamiltonian for the
microwave billiard with the embedded ferrite are determined experimentally as
functions of the magnetization of the ferrite.",0702041v1
2007-08-20,Eigen electric moments of magnetic-dipolar modes in quasi-2D ferrite disk particles,"A property associated with a vortex structure becomes evident from an
analysis of confinement phenomena of magnetic oscillations in a quasi-2D
ferrite disk with a dominating role of magnetic-dipolar
(non-exchange-interaction) spectra. The vortices are guaranteed by the chiral
edge states of magnetic-dipolar modes which result in appearance of eigen
electric moments oriented normally to the disk plane. Due to the
eigen-electric-moment properties, a ferrite disk placed in a microwave cavity
is strongly affected by the cavity RF electric field with a clear evidence for
multi-resonance oscillations. For different cavity parameters, one may observe
the ""resonance absorption"" and ""resonance repulsion"" behaviors.",0708.2678v1
2008-05-05,Magnetoelectric oscillations in quasi-2D ferrite disk particles,"In this paper we show that magnetic-dipolar-mode (MDM) oscillations of a
quasi-2D ferrite disk are characterized by unique symmetry features with
topological phases resulting in appearance of the magnetoelectric (ME)
properties. The entire ferrite disk can be characterized as a pair of two,
electric and magnetic, coupled eigen moments. However, there is no a ""glued
pair"" of two dipoles. An external electromagnetic field in the near-field
region ""views"" such a ME particle, as a system with a normally oriented eigen
electric moment and an in-plane rotating eigen magnetic dipole moment.",0805.0518v1
2013-07-18,Interaction effect detected by compared of the irreversible and remanent initial magnetization curves in Ni-Cu-Zn ferrites,"A new technique for estimation of magnetic interaction effects of initial
magnetization curves has been proposed. It deals with remanence, and initial
irreversible magnetization, curves. The method is applied for single-phase
polycrystalline Ni0.85-xCu0.15ZnxFe2O4, (x = 0, 0.2, 0.4 and 0.6), which were
synthesized by a standard ceramic technology. A study of the initial reversible
and irreversible magnetization processes in ferrite materials was carried out.
The field dependence of the irreversible, and reversible, magnetizations was
determined by magnetic losses of minor hysteresis loops obtained from different
points of an initial magnetization curve. The influence of Zn-substitutions in
Ni-Cu ferrites over irreversible magnetization processes and interactions in
magnetic systems has been analyzed.",1307.4881v1
2014-02-09,Synthesis of Fe3O4@CoFe2O4@MnFe2O4 trimagnetic core/shell/shell nanoparticles,"We report the synthesis and characterization of original 'multishell'
magnetic nanoparticles made of a soft core (magnetite) covered with two
successive shells: a hard one (cobalt ferrite) and then a soft one (manganese
ferrite). Our results show that contrary to expectations from simple models in
which the coercivity of a bimagnetic core/shell nanoparticle depends simply on
the proportion of soft and hard phases within that particle, the addition of a
second shell made of a soft ferrite material enhances the coercivity. Taking
into account the interactions between the shells themselves and the core may
thus be necessary to understand the magnetic properties of such nanoparticles.",1402.1950v1
2013-08-01,Control of magnetization reversal in oriented Strontium Ferrite thin films,"Oriented Strontium Ferrite films with the c axis orientation were deposited
with varying oxygen partial pressure on Al2O3(0001) substrate using PLD
technique. The angle dependent magnetic hysteresis, remanent coercivity and
temperature dependent coercivity had been employed to understand the
magnetization reversal of these films. It was found that the Strontium Ferrite
thin film grown at lower (higher) oxygen partial pressure shows
Stoner-Wohlfarth type (Kondorsky like) reversal. The relative importance of
pinning and nucleation processes during magnetization reversal is used to
explain the type of the magnetization reversal with different oxygen partial
pressure during growth.",1308.0171v1
2019-10-15,3D Field Simulation Model for Bond Wire On-Chip Inductors Validated by Measurements,"This paper proposes 3D field simulation models for different designs of
integrated bond wire on-chip inductors. To validate the simulation models,
prototypes for three designs with air and ferrite cores are manufactured and
measured. For air core inductors, high agreement between simulation and
measurement is obtained. For ferrite core inductors, accurate models require an
exact characterization of the ferrite material. These models enable the
prediction of magnetic field influences on underlying integrated circuits.",1910.06831v1
2018-12-16,Yttrium-substituted Mg-Zn ferrites: correlation of physical properties with Yttrium content,"Yttrium (Y) substituted Mg Zn ferrites with the compositions of
Mg0.5Zn0.5YxFe2 xO4 have been synthesized by conventional standard ceramic
technique. The effect of Y3+ substitution on the structural, electrical,
dielectric and magnetic properties of Mg Zn ferrites has been studied.",1812.06370v2
2019-02-23,Tailoring the crack-tip microstructure: A novel approach,"This investigation demonstrates a way to innovatively modify the ferritic
microstructure at a local scale, particularly at the failure prone area such as
Charpy V-notch (CVN) root. Tensile pre-strain (PS) up to 6 percent and 12
percent were employed before annealing (An) the samples at 650{\deg}C for 15
minutes. Ferrite grain size increased sharply and gradually (along the distance
ahead of the notch root) within the microstructurally modified region in 6-12
percent pre-strained and annealed samples, respectively. Critical strain which
promotes strain induced boundary migration (SIBM), was found to be 0.1 which
resulted in abnormally coarse ferrite grains.",1902.08797v1
2019-08-04,Transparent Negative Index of Refraction Metamaterial Using a Wire Array in a Magnetic Host,"We have made measurements of microwave transmission over the 12 - 18 GHz
range and through a simple metamaterial exhibiting a negative index of
refraction. The metamaterial consisted of an array of wires cladded in
dielectric embedded in a magnetic ferrite. The ferrite replaced the cut-ring
structure usually used to create the negative permeability. The dielectric
cladding decoupled the ferrite from the wires, thereby allowing the wire array
permittivity to be simultaneously negative with the permeability. The
simplicity of the design allows for miniaturization of potential microwave
devices based on this metamaterial.",1908.01378v1
2023-03-08,Construction and Testing of a Common Mode Choke for Cryogenic Detector Pre-Amplifiers,"Common-mode choke inductors are useful tools for resolving grounding issues
in large detector systems. Using inductive components on cryogenic
pre-amplifier boards has so far been prevented by the poor low-temperature
performance of common ferrite materialssuch as NiZn and MnZn. Recentlydeveloped
nanocrystallineand amorphous ferrite materials promise improved performance up
to the point where using magnetics at liquid mitrogen temperatures becomes
feasible. This research applies the work of Yin et al. on characterizing
ferrite materials by constructing and testing a common mode choke inductor for
use on detector pre-amplifiers for the ELT first generation instruments.",2303.04541v1
2003-05-19,The anapole moments in disk-form MS-wave ferrite particle,"The anapole moments describe the parity-violating parity-odd,
time-reversal-even couplings between elementary particles and the
electromagnetic (EM) field. Surprisingly, the anapole-like moment properties
can be found in certain artificially engineered physical systems. In
microwaves, ferrite resonators with multi-resonance magnetostatic-wave
(MS-wave) oscillations may have sizes two-four orders less than the free-space
EM wavelength at the same frequency. MS-wave oscillations in a ferrite sample
occupy a special place between the pure electromagnetic and spin-wave
(exchange) processes. The energy density of MS-wave oscillations is not the
electromagnetic-wave density of energy and not the exchange energy density as
well. These microscopic oscillating objects -- the particles -- may interact
with the external EM fields by a very specific way, forbidden for the classical
description. To describe such interactions, the quantum mechanical analysis
should be used. The presence of surface magnetic currents is one of the
features of MS oscillations in a normally magnetized ferrite disk resonator.
Because of such magnetic currents, MS oscillations in ferrite disk resonators
become parity violating. The parity-violating couplings between disk-form
ferrite particles and the external EM field should be analyzed based on the
notion of an anapole moment.",0305431v1
2007-12-14,Electric self inductance of quasi-2D magnetic-dipolar-mode ferrite disks,"An electric current flowing around a loop produces a magnetic field and hence
a magnetic flux through the loop. The ratio of the magnetic flux to the
electric current is called the (magnetic) self inductance. Can there be a dual
situation with a magnetic current flowing around a loop and producing an
electric field and hence an electric flux through the loop? Following the
classical electrodynamics laws an answer to this question should be negative.
Nevertheless special spectral properties of magnetic dipolar modes in a
quasi-2D ferrite disk show there are the double-valued-function loop magnetic
currents which may produce eigen electric fields and hence eigen electric
fluxes through the loop. In this case one can definitely introduce the notion
of the electric self inductance as the ratio of the electric flux to the
magnetic current. In this paper we show experimentally that in the
magnetic-dipolar-mode ferrite disks there exist eigen electric fluxes. These
fluxes are very sensitive to permittivity parameters of materials abutting to
the ferrite disk. Dielectric samples above a ferrite disk with a higher
permittivity than air confine the electric field closely outside the ferrite,
thereby changing the loop magnetic currents and thus transforming the
magnetic-dipolar-mode oscillating spectrum.",0712.2305v1
2014-07-14,Bismuth ferrite as low-loss switchable material for plasmonic waveguide modulator,"We propose new designs of plasmonic modulators, which can be utilized for
dynamic signal switching in photonic integrated circuits. We study performance
of plasmonic waveguide modulator with bismuth ferrite as an active material.
The bismuth ferrite core is sandwiched between metal plates
(metal-insulator-metal configuration), which also serve as electrodes so that
the core changes its refractive index under applied voltage by means of partial
in-plane to out-of-plane reorientation of ferroelectric domains in bismuth
ferrite. This domain switch results in changing of propagation constant and
absorption coefficient, and thus either phase or amplitude control can be
implemented. Efficient modulation performance is achieved because of high field
confinement between the metal layers, as well as the existence of mode cut-offs
for particular values of the core thickness, making it possible to control the
signal with superior modulation depth. For the phase control scheme, {\pi}
phase shift is provided by 0.8-{\mu}m length device having propagation losses
0.29 dB/{\mu}m. For the amplitude control, we predict up to 38 dB/{\mu}m
extinction ratio with 1.2 dB/{\mu}m propagation loss. In contrast to previously
proposed active materials, bismuth ferrite has nearly zero material losses, so
bismuth ferrite based modulators do not bring about additional decay of the
propagating signal.",1407.3734v1
2017-08-16,"Role of pinning mechanism in co-precipitation derived cobalt rich, cobalt ferrite nanoparticles","Cobalt ferrite nanoparticles have been synthesized using a co-precipitation
approach. Co:Fe precursor ratio is varied over a certain window (1.05 to 1.2).
It is observed that the 1.15:2 precursor ratio gives better phase control but
poor coercivity. On the other hand, 1.05:2 precursor ratio results in
substantially better coercivity values (274kA/m; almost 300% the value reported
for co-precipitated cobalt ferrite by Praveena et al.), but moderate BH product
maximum (2.25 kJ/m3; ~ comparable to many reports on cobalt ferrite
nanoparticles so far). The nanoparticles with best coercivity are annealed at
873K for varying durations (2, 4, 6, 12 hrs). It is observed that the
coercivity drops drastically (almost by 80%) after annealing for 2 hours.
However thereafter coercivity and saturation magnetization improves marginally
with increasing duration of annealing. These studies, along with
thermogravimetric analysis, and infrared spectroscopic results indicate that a
hydroxide nanophase based flux pinning mechanism at the grain boundary plays an
important role in explaining the observed magnetic property trends. It is
believed that this result will be generically helpful in developing soft
chemically derived ferrites with higher coercivity and moderate (BH)max.
However to develop plausible applications using the reported ferrites that use
nanophase flux pinning, soft materials and device processing methods will need
to be explored.",1708.04839v1
2012-04-01,Topological-phase effects and path-dependent interference in microwave structures with magnetic-dipolar-mode ferrite particles,"Different ways exist in optics to realize photons carrying nonzero orbital
angular momentum. Such photons with rotating wave fronts are called twisted
photons. In microwaves, twisted fields can be produced based on small ferrite
particles with magnetic-dipolar-mode (MDM) oscillations. Recent studies showed
strong localization of the electric and magnetic energies of microwave fields
by MDM ferrite disks. For electromagnetic waves irradiating MDM disks, these
small ferrite samples appear as singular subwavelength regions with time and
space symmetry breakings. The fields scattered by a MDM disk are characterized
by topologically distinctive power-flow vortices and helicity structures. In
this paper we analyze twisted states of microwave fields scattered by MDM
ferrite disks. We show that in a structure of the fields scattered by MDM
particles, one can clearly distinguish rotating topological-phase dislocations.
Specific long-distance topological properties of the fields are exhibited
clearly in the effects of path-dependent interference with two coupled MDM
particles. Such double-twisted scattering is characterized by topologically
originated split-resonance states. Our studies of topological-phase effects and
path-dependent interference in microwave structures with MDM ferrite particles
are based on numerical analysis and recently developed analytical models. We
present preliminary experimental results aimed to support basic statements of
our studies.",1204.0177v1
2020-04-15,Synthesis optimization of Zn-Mn ferrites for magnetic fluid aplications,"Mn-Zn ferrite nanoparticles have been subject of increasing research due to
their desired properties for a wide range of applications. These properties
include nanometer particle size control, tunable magnetic properties and low
toxicity, providing these ferrites with the necessary requirements for cancer
treatment via magnetic hyperthermia. During this master thesis, powders of
Mn1-xZnxFe2O4 (x=0; 0.5; 0.8; 1) were synthesized via the sol-gel
autocombustion and hydrothermal methods, aiming to optimize their structural
and magnetic properties for further application in a ferrofluid. Samples were
characterized by XRD, SQUID, SEM, TEM and magnetic induction heating (MIH)
techniques. The XRD diffractograms of hydrothermally produced samples present
spinel crystal structure with high single-phase percentage (>88%). Rietveld
refinement and Williamson-Hall analysis reveal a decrease of lattice constant
and crystallite size with increase of Zn/Mn ratio. TEM images reveal narrow
particle size distributions and decrease of the mean particle size with
increase of Zn/Mn. SQUID results show that the increase of Zn results in a
decrease of saturation magnetization and remnant magnetization. More
noticeably, the M(T) curves present a shift in the samples magnetic ordering
temperature towards lower temperatures with the increase of Zn content, from
~556 to ~284 K. The MIH experiment also unveil a decrease in the heating rate
with the increase of Zn. Nanocrystals of Mn-Zn ferrite produced by hydrothermal
method present better crystallinity and magnetic properties than the sol-gel
auto-combustion samples. The hydrothermally synthesized samples revealed
dependence of its structural and magnetic properties with Mn/Zn ratio.The
magnetic ordering temperature of these ferrites can be used as a
self-controlled mechanism of heating, raising these ferrites to a class of
smart materials.",2004.07006v2
2023-01-04,Preparation and Characterization of NixMn0.25-xMg0.75Fe2O4 Nano-ferrite as NO2 Gas Sensing Material,"NixMn0.25-xMg0.75Fe2O4 nano-ferrites (where x = 0.00, 0.05, 0.10, 0.15 and
0.20) were produced via sol-gel auto-combustion technique. Investigations were
done into how the incorporation of Ni ions affects the Mn0.25Mg0.75Fe2O4
ferrite's structure, morphological, magnetic, and NO2 gas sensing features. All
the samples are single-phase, based on the structural study utilizing the X-ray
diffraction (XRD) pattern. In terms of the structure of the cubic spinel,
according to the XRD study, the crystallite sizes range from 24.30 to 28.32 nm,
indicating nano-crystallinity. The synthesis of spherical nanoparticles with a
small modification in particle size distribution was verified via FE-SEM
images. The study found that the size of particles is tiny enough to act
superparamagnetically. The area of hysteresis loop is almost non-existing, thus
reflecting typical soft magnetic materials according to magnetic measurements
by VSM carried out at room temperature. Furthermore, the conductance responses
of the NixMn0.25-xMg0.75Fe2O4 nano-ferrite were measured by exposing the
ferrite to oxidizing (NO2) gas at different operating temperatures. The results
show that the sensor boasts shorter response and recovery times, as well as a
higher sensitivity 707.22% of the sample (x=0.20) for nano-ferrite.",2301.01728v1
2007-07-03,A new concept and design of ferrite-based microwave vortex devices,"In microwave resonant systems with ferrite samples, one becomes faced with
specific phase relations for the electromagnetic fields. Such specific phase
relations may lead to appearance of nontrivial states: electromagnetic
vortices. This paper provides some general ideas and design principles for
microwave devices with the field vortex structures.",0707.0350v1
2008-12-12,Magnetoelectric Effect for Novel Microwave Device Applications,"In a normally magnetized thin-film ferrite disk with magnetic-dipolar modes,
one can observe magnetoelectric oscillations. Such magnetoelectric properties
of an electrically small sample can be considered as very attractive phenomena
in microwaves. In this paper we discuss the question on novel microwave device
applications based on ferrite magnetoelectric particles.",0812.2343v2
2009-04-20,Quasi-Optical Characterization of Dielectric and Ferrite Materials,"Quasi-Optical Characterization of Dielectric and Ferrite Materials are made
in the millimeter-submillimeter range by using a Quasi-Optical (QO) benches
that can be relatively compact, typically of the order 10cm wide and 1m long.",0904.3069v1
2014-07-17,Magnetic Properties of Bismuth Ferrite Nanopowder Obtained by Mechanochemical Synthesis,"Multiferroic bismuth ferrite (BiFeO3) nanopowders have been obtained in room
temperature by mechanical synthesis. Depending on the post-synthesis processing
the nanopowders have exhibited differences in the mean sizes, presence of
amorphous layer and/or secondary phases. Extended magnetic study performed for
fresh, annealed and hot-pressed nanopowders have revealed substantial
improvement of the magnetic properties in the as-prepared powder.",1407.4657v1
2018-04-16,Unidirectional Loop Metamaterials (ULM) as Magnetless Artificial Ferrimagnetic Materials: Principles and Applications,"This paper presents an overview of Unidirectional Loop Metamaterial (ULM)
structures and applications. Mimicking electron spin precession in ferrites
using loops with unidirectional loads (typically transistors), the ULM exhibits
all the fundamental properties of ferrite materials, and represents the only
existing magnetless ferrimagnetic medium. We present here an extended
explanation of ULM physics and unified description of its component and system
applications.",1804.08719v1
2017-04-25,Characterization of Zinc oxide & Aluminum Ferrite and Simulation studies of M-H plots of Cobalt/Cobaltoxide,"Zinc oxide and Aluminum Ferrite were prepared Chemical route. The samples
were characterized by XRD and VSM. Simulation of M-H plots of Co/CoO thin films
were performed. Effect of parameters was observed on saturation magnetization.",1705.00525v2
2003-06-19,Resonance magnetoelectric effects in layered magnetostrictive-piezoelectric composites,"Magnetoelectric interactions in bilayers of magnetostrictive and
piezoelectric phases are mediated by mechanical deformation. Here we discuss
the theory and companion data for magnetoelectric (ME) coupling at
electromechanical resonance (EMR) in a ferrite-lead zirconate titanate (PZT)
bilayer. Estimated ME voltage coefficient versus frequency profiles for nickel,
cobalt, or lithium ferrite and PZT reveal a giant ME effect at EMR with the
highest coupling expected for cobalt ferrite-PZT. Measurements of resonance ME
coupling have been carried out on layered and bulk composites of nickel
ferrite-PZT. We observe a factor of 40-600 increase in ME voltage coefficient
at EMR compared to low frequency values. Theoretical ME voltage coefficients
versus frequency profiles are in excellent agreement with data. The resonance
ME effect is therefore a novel tool for enhancing the field conversion
efficiency in the composites.",0306513v1
2003-08-08,Low frequency and Microwave Magnetoelectric Effects in Thick Film Heterostructures of Lithium Zinc Ferrite and Lead Zirconate Titanate,"Magnetoelectric (ME) coupling at low frequencies and at x-band have been
investigated in layered samples containing zinc substituted lithium ferrite and
lead zirconate titanate (PZT). Multilayers of Li0.5-x/2ZnxFe2.5-x/2O4 (LZFO)
(x=0-0.4) and PZT were prepared by lamination and sintering of thick films. At
low frequencies (10-1000 Hz), the ME voltage coefficient for transverse fields
is higher than for longitudinal fields. With Zn substitution in the ferrite,
transverse coupling increases to a maximum for x=0.3 and then decreases for
higher x. Analysis based on our model for a bilayer implies an efficient
magneto-mechanical coupling with Zn substitution, resulting in strong ME
interactions. Microwave ME coupling is studied through measurements of shift in
the ferromagnetic resonance field due to an applied electric field. Estimated
ME constants from such data are in agreement with our model for a ferrite-PZT
bilayer.",0308171v1
2003-10-23,On implementation of ferrite magnetostatic/magnetoelectric particles for quantum computation,"We consider an implementation of quantum gates for quantum computation using
magnetostatic/magnetoelectric (MS/ME) macroscopically quantized states in small
ferrite disks. Confinement phenomena for MS oscillations in a normally
magnetized ferrite disk show typical atomic properties like discrete energy
levels. Because of discrete energy eigenstates of MS oscillations, the
oscillating system is described as a collective motion of quasi-particles - the
light magnons. A macroscopic quantum analysis of MS oscillations underlines the
physics of quantized ME oscillating spectrums in ferrite disks with surface
electrodes. We discuss possible technologies for physical realization of new
logic gates based on MS/ME-particle qubits.",0310558v1
2009-08-30,Magnetic-dipolar-mode vortices and microwave subwavelength metamaterials,"There has been a surge of interest in the subwavelength confinement of the
electromagnetic fields. It is well known that in optics the subwavelength
confinement can be obtained due to surface plasmon (quasielectrostatic)
oscillations. In this paper we propose to realize the subwavelength confinement
in microwaves due to dipolar-mode (quasimagnetostatic) magnon oscillations in
ferrite particles. Our studies of interactions between microwave
electromagnetic fields and small ferrite particles with magnetic-dipolar-mode
(MDM) oscillations show strong localization of electromagnetic energy. MDM
oscillations in a ferrite disk are origins of topological singularities
resulting in Poynting-vector vortices and symmetry breakings of the microwave
near fields. We show that new subwavelength microwave metamaterials can be
realized based on a system of interacting MDM ferrite disks. The volume- and
surface-wave propagation of electromagnetic signals in the proposed dense
metamaterials will be characterized by topological phase variations. The
MDM-particle-metamaterial concept opens a significantly new area of research.
In particular, there is a perspective for creation of engineered
electromagnetic fields with unique symmetry properties.",0908.4383v1
2011-03-30,Giant coercivity of dense nanostructured spark plasma sintered barium hexaferrite,"Due to the limited rare-earth elements resources, ferrite magnets need to be
improved drastically. Ideally, for a true hard magnet, the coercive field
should be larger than the saturation magnetization, which is not yet realized
for ferrites. Thus, an alternative can be found in making very fine grain
ferrite magnets, but it is usually impossible to get small grains and dense
material together. In this paper, it is shown that the spark plasma sintering
method is able to produce approximately 80% of dense material with crystallites
smaller than 100 nm. The as-prepared bulk sintered anisotropic magnets exhibits
coercive field of 0.5 T which is approximately 60% of the theoretical limit and
only a few percentage below that of loose nanopowders. As a result, the magnets
behave nearly ideal (-1.18 slope in the BH plane second quadrant) and the
energy product reaches 8.8 kJ m-3, the highest value achieved in the isotropic
ferrite magnet to our knowledge.",1103.5840v1
2012-03-18,"Structural, magnetic, and optical properties of zinc- and copper- substituted nickel ferrite nanocrystals","Ferrite nanocrystals are interesting material due to their rich physical
properties. Here we add nonmagnetic dopants Zn and Cu to nickel ferrite
nanocrystals, Ni1-xMxFe2O4 (0<=x<=1, M{\in}{Cu, Zn}), and characterize how
relevant properties of the samples are modified accordingly. Basically, these
dopings cause a rearrangement of Fe+3 ions into the two preexisting octahedral
and tetrahedral sites. In fact, this, we show, induces pertinent magnetic
properties of the doped samples. In the case of the Cu-doping, the Jahn-Teller
effect also emerges, which we identify through the FTIR Spectroscopy of the
samples. Moreover, we show an increase in the lattice parameters of the doped
samples, as well a superparamagnetic behavior for the doped samples is shown,
while the Jahn-Teller effect precludes a similar behavior in the CuFe2O4
nanocrystals. The influences of Zn and Cu substitutions are investigated on the
optical properties of nickel ferrite nanocrystals by photoluminescence
measurement at room temperature.",1203.3924v1
2016-07-17,Third Order Perturbed Heisenberg Hamiltonian of Thick Spinel Ferrite Films,"The third order perturbed Heisenberg Hamiltonian was employed to investigate
the spinel thick nickel ferrite films. The variation of energy up to N=10000
was studied. At N=75, the energy required to rotate from easy to hard direction
is very small. For film with N=10000, the first major maximum and minimum can
be observed at 202 and 317 degrees, respectively. This curve shows some abrupt
changes after introducing third order perturbation. The maximum energy of this
curve is higher than that of spinel thick ferrite films with second order
perturbed Heisenberg Hamiltonian. At some values of stress induced anisotropy,
the maximum energy is less than that of spinel thick ferrite films with second
order perturbed Heisenberg Hamiltonian derived by us previously.",1611.02230v1
2017-01-18,Azimuthally unidirectional transport of energy in magnetoelectric fields. Topological Lenz effect,"Magnetic dipolar modes (MDMs) in a quasi 2D ferrite disk are microwave energy
eigenstate oscillations with topologically distinct structures of rotating
fields and unidirectional power flow circulations. At the first glance, this
might seem to violate the law of conservation of an angular momentum, since the
microwave structure with an embedded ferrite sample is mechanically fixed.
However, an angular momentum is seen to be conserved if topological properties
of electromagnetic fields in the entire microwave structure are taken into
account. In this paper we show that due to the topological action of the
azimuthally unidirectional transport of energy in a MDM resonance ferrite
sample there exists the opposite topological reaction on a metal screen placed
near this sample. We call this effect topological Lenz effect. The topological
Lenz law is applied to opposite topological charges, one in a ferrite sample
and another on a metal screen. The MDM originated near fields, the
magnetoelectric (ME) fields, induce helical surface electric currents and
effective charges on a metal. The fields formed by these currents and charges
will oppose their cause.",1701.05185v1
2017-04-04,Magnetic Dipole Interaction and Total Magnetic Energy of Lithium Ferrire Thin Films,"The total magnetic energy of Lithium ferrite thin films was determined using
the classical Heisenberg Hamiltonian. The short range magnetic dipole
interactions between spins within one unit cell and the interactions between
spins in two adjacent unit cells have been determined in order to find the
total magnetic energy of lithium ferrite films. Only the spin pairs with
separation less than cell constant have been taken into account to calculate
dipole interaction and spin exchange interaction. Theoretically several easy
and hard directions of lithium ferrite film were found for one set of energy
parameters included in our modified Heisenberg Hamiltonian. The dependence of
total magnetic energy of a lithium ferrite film on number of unit cells, spin
exchange interaction, dipole interaction, second order magnetic anisotropy,
fourth order magnetic anisotropy, internal applied magnetic field and stress
induced magnetic anisotropy has been explained in this manuscript.",1704.03314v1
2013-09-16,Epitaxial Growth of Spinel Cobalt Ferrite Films on MgAl$_2$O$_4$ Substrates by Direct Liquid Injection Chemical Vapor Deposition,"The direct liquid injection chemical vapor deposition (DLI-CVD) technique has
been used for the growth of cobalt ferrite (CFO) films on (100)-oriented
MgAl$_2$O$_4$ (MAO) substrates. Smooth and highly epitaxial cobalt ferrite thin
films, with the epitaxial relationship $\mathrm{MAO} (100)\:[001] \parallel
\mathrm{CFO} (100)\:[001]$, are obtained under optimized deposition conditions.
The films exhibit bulk-like structural and magnetic properties with an
out-of-plane lattice constant of $8.370\;\mathrm{\AA}$ and a saturation
magnetization of $420\;\mathrm{kA/m}$ at room temperature. The Raman spectra of
films on MgAl$_2$O$_4$ support the fact that the Fe$^{3+}$- and the
Co$^{2+}$-ions are distributed in an ordered fashion on the B-site of the
inverse spinel structure. The DLI-CVD technique has been extended for the
growth of smooth and highly oriented cobalt ferrite thin films on a variety of
other substrates, including MgO, and piezoelectric lead magnesium niobate-lead
titanate and lead zinc niobate-lead titanate substrates.",1309.4031v1
2018-08-10,Role of disconnections in mobility of the austenite-ferrite inter-phase boundary in Fe,"Austenite ({\gamma}-Fe, face centered cubic (FCC)) to ferrite ({\alpha}-Fe,
body centered cubic (BCC)) phase transformation in steel is of great
significance from the point of view of industrial applications. In this work,
using classical molecular dynamics simulations, we study the atomistic
mechanisms involved during the nucleation and growth of the ferrite phase
embedded in an austenite phase. We find that the disconnections present at the
inter-phase boundary can act as the nucleation centers for the ferrite phase.
Relatively small interface velocities (1.19 - 4.67 m/s) confirm a phase change
via massive transformation mechanism. Boundary mobilities obtained in a
temperature range of 1000 to 1400 K show an Arrhenius behavior, with activation
energies ranging from 30 - 40 kJ/mol.",1808.03432v2
2020-10-28,On the happiness of ferroelectric surfaces and its role in water dissociation: the example of bismuth ferrite,"We investigate, using density functional theory, how the interaction between
the ferroelectric polarization and the chemical structure of the (001) surfaces
of bismuth ferrite influences the surface properties and reactivity of this
material. A precise understanding ofthe surface behavior of ferroelectrics is
necessary for their use in surface science applications such as catalysis as
well as for their incorporation in microelectronic devices. Using the (001)
surface of bismuth ferrite as a model system we show that the most
energetically favoured surface geometries are combinations of surface
termination and polarization direction that lead to uncharged, stable surfaces.
On the unfavorable charged surfaces, we explore the compensation mechanisms of
surface charges provided by the introduction of point defects and adsorbates,
such as water. Finally, we propose that the special surface properties of
bismuth ferrite (001) could be used to produce an effective water splitting
cycle through cyclic polarization switching.",2010.14895v1
2022-05-12,"Structural, Dielectric, and Electrical Transport Properties of Al3+ Substituted Nanocrystalline Ni-Cu Spinel Ferrites Prepared Through the Sol-Gel Route","In this study, a series of nanocrystalline ferrites of Ni0.7Cu0.30AlxFe2-xO4
(x=0.00 to 0.10 with a step of 0.02) has been synthesized through the sol-gel
auto combustion technique. The structural, morphological, dielectric, and
electrical properties of the Ni-Cu spinel ferrite nanoparticles are analyzed
due to the substitution of Al3+ content. The crystalline and structural
characteristics of the prepared nanoparticles (NPs) have been studied employing
the x-ray diffraction (XRD) spectra and FTIR analysis. The extracted XRD
patterns assure the single-phase cubic spinel structure of all samples with
homogeneity and no impurity, which indicates the yielding of high crystalline
NPs. A slight decrease of average grain size with increment of Al3+ content is
observed in the surface morphological study carried out by the field emission
scanning electron microscopy (FESEM). The studied materials are found in
semi-spherical shapes, showing the multi-domain grains separated by grain
boundaries with some agglomerations. The chemical composition study for the
synthesized NI-Cu spinel ferrites using energy dispersive x-ray (EDX) ensures
the presence of each component in appropriate proportions in each sample.",2205.06233v1
2023-05-24,Time-reversal Invariance Violation and Quantum Chaos Induced by Magnetization in Ferrite-Loaded Resonators,"We investigate the fluctuation properties in the eigenfrequency spectra of
flat cylindrical microwave cavities that are homogeneously filled with
magnetized ferrite. These studies are motivated by experiments in which only
small pieces of ferrite were embedded in the cavity and magnetized with an
external static magnetic field to induce partial time-reversal (T ) invariance
violation. We use two different shapes of the cavity, one exhibiting an
integrable wave dynamics, the other one a chaotic one. We demonstrate that in
the frequency region where only transverse-magnetic modes exist, the
magnetization of the ferrites has no effect on the wave dynamics and does not
induce T -invariance violation whereas it is fully violated above the cutoff
frequency of the first transverse-electric mode. Above all, independently of
the shape of the resonator, it induces a chaotic wave dynamics in that
frequency range in the sense that for both resonator geometries the spectral
properties coincide with those of quantum systems with a chaotic classical
dynamics and same invariance properties under application of the generalized T
operator associated with the resonator geometry.",2305.14753v1
2024-02-19,Broadband ferromagnetic resonance in Mn-doped Li ferrite nanoparticles,"Lithium ferrites are well known materials due to their numerous technological
applications especially in microwave devices. Mn-doped lithium ferrite
nanoparticles were prepared by sol-gel technique by means of Pechini method,
and then annealed at different temperatures in 250 to 1000 {\deg}C range. XRD
confirms spinel formation with particle size in the 15 to 200 nm range, with
increased size with annealing temperature. Microwave magnetoabsorption data of
annealed lithium ferrite nanoparticles, obtained with a broadband system based
on a network analyzer operating up to 8.5 GHz are presented. At fields up to
200 mT we can observe a broad absorption peak that shifts to higher frequencies
with magnetic field according to ferromagnetic resonance theory. The amplitude
of absorption, up to 85%, together with the frequency width of about 4.5 GHz
makes this material suitable as wave absorber. Samples annealed at higher
temperatures show a behaviour similar to polycrystalline samples, thus
suggesting their multidomain character",2402.12096v1
2001-07-05,"Two Modes of Solid State Nucleation - Ferrites, Martensites and Isothermal Transformation Curves","When a crystalline solid such as iron is cooled across a structural
transition, its final microstructure depends sensitively on the cooling rate.
For instance, an adiabatic cooling across the transition results in an
equilibrium `ferrite', while a rapid cooling gives rise to a metastable twinned
`martensite'. There exists no theoretical framework to understand the dynamics
and conditions under which both these microstructures obtain. Existing theories
of martensite dynamics describe this transformation in terms of elastic strain,
without any explanation for the occurence of the ferrite. Here we provide
evidence for the crucial role played by non-elastic variables, {\it viz.},
dynamically generated interfacial defects. A molecular dynamics (MD) simulation
of a model 2-dimensional (2d) solid-state transformation reveals two distinct
modes of nucleation depending on the temperature of quench. At high
temperatures, defects generated at the nucleation front relax quickly giving
rise to an isotropically growing `ferrite'. At low temperatures, the defects
relax extremely slowly, forcing a coordinated motion of atoms along specific
directions. This results in a twinned critical nucleus which grows rapidly at
speeds comparable to that of sound. Based on our MD results, we propose a
solid-state nucleation theory involving the elastic strain and non-elastic
defects, which successfully describes the transformation to both a ferrite and
a martensite. Our work provides useful insights on how to formulate a general
dynamics of solid state transformations.",0107098v2
2003-03-11,Magnetic artificial atoms based on thin-film ferrite disk particles,"Semiconductor quantum wells can be considered as an example of artificial
atoms. Following the ideas used in the effective-mass theory, one can describe
electron states in the quantum-well structure based on the Schrodinger-like
equation for the envelope function. In recent years, there has been a renewed
interest in high frequency dynamic properties of finite size magnetic
structures. In a series of new publications, confinement phenomena of
high-frequency magnetization dynamics in magnetic particles have been the
subject of much experimental and theoretical attention. Till now, however,
there are no phenomenological models of a ferrite particle with high-frequency
magnetization dynamics that use the effective-mass approximation and the
Schrodinger-like equation to analyze energy eigenstates of a whole
ferrite-particle system, similarly to semiconductor quantum wells.
Magnetostatic (MS) oscillations in ferrite samples have the wavelength much
smaller than the electromagnetic wavelength at the same frequency and, at the
same time, much larger than the exchange-interaction spin wavelength. This
intermediate position between the pure electromagnetic and spin-wave
(exchange-interaction) processes reveals very special behaviors of the
geometrical effects. The confined effects for MS oscillations in normally
magnetized thin-film ferrite disks demonstrate very unique properties of
artificial atomic structures.",0303196v1
2009-09-27,Space-time symmetry violation of the fields in quasi-2D ferrite particles with magnetic-dipolar-mode oscillations,"In magnetic systems with reduced dimensionality, the effects of dipolar
interactions allow the existence of long-range ordered phases. Long-range
magnetic-dipolar interactions are at the heart of the explanation of many
peculiar phenomena observed in nuclear magnetic resonance, ferromagnetic
resonance, and Bose-Einstein-condensate structures. In this paper we show that
magnetic-dipolar-modes (MDMs) in quasi-2D ferrite disks are characterized by
symmetry breaking effects. Our analysis is based on postulates about a physical
meaning of the magnetostatic-potential function as a complex scalar wave
function, which presumes the long-range phase correlations. An important
feature of the MDM oscillations in a ferrite disk concerns the fact that a
structure with symmetric parameters and symmetric basic equations goes into
eigenstates that are not space-time symmetric. The proper solutions are found
based on an analysis of magnetostatic-wave propagation in a helical coordinate
system. For a ferrite disk, we show that while a composition of two helical
waves may acquire a geometrical phase over-running of during a period, every
separate helical wave has a dynamical phase over-running of and so behaves as a
double-valued function. We demonstrate that unique topological structures of
the fields in a ferrite disk are intimately related to the symmetry breaking
properties of MDM oscillations. The solutions give the MDM power-flow-density
vortices with cores at the disk center and azimuthally running waves of
magnetization. One can expect that the proposed models of long-range ordered
phases and space-time violation properties of magnetic-dipolar interactions can
be used in other magnetic structures, different from the
ferromagnetic-resonance system with reduced dimensionality.",0909.4920v1
2013-07-18,Numerical response of the magnetic permeability as a funcion of the frecuency of NiZn ferrites using Genetic Algorithm,"The magnetic permeability of a ferrite is an important factor in designing
devices such as inductors, transformers, and microwave absorbing materials
among others. Due to this, it is advisable to study the magnetic permeability
of a ferrite as a function of frequency.
  When an excitation that corresponds to a harmonic magnetic field \textbf{H}
is applied to the system, this system responds with a magnetic flux density
\textbf{B}; the relation between these two vectors can be expressed as
\textbf{B}=$\mu(\omega)$ \textbf{H} . Where $\mu$ is the magnetic permeability.
  In this paper, ferrites were considered linear, homogeneous, and isotropic
materials. A magnetic permeability model was applied to NiZn ferrites doped
with Yttrium.
  The parameters of the model were adjusted using the Genetic Algorithm. In the
computer science field of artificial intelligence, Genetic Algorithms and
Machine Learning does rely upon nature's bounty for both inspiration nature's
and mechanisms. Genetic Algorithms are probabilistic search procedures which
generate solutions to optimization problems using techniques inspired by
natural evolution, such as inheritance, mutation, selection, and crossover.
  For the numerical fitting usually is used a nonlinear least square method,
this algorithm is based on calculus by starting from an initial set of variable
values. This approach is mathematically elegant compared to the exhaustive or
random searches but tends easily to get stuck in local minima. On the other
hand, random methods use some probabilistic calculations to find variable sets.
They tend to be slower but have greater success at finding the global minimum
regardless of the initial values of the variables",1307.5007v1
2015-03-01,Microwave magnetoelectric fields: An analytical study of topological characteristics,"The near fields originated from a small quasi-two-dimensional ferrite disk
with magnetic-dipolar-mode (MDM) oscillations are the fields with broken dual
(electric-magnetic) symmetry. Numerical studies show that such fields, called
the magnetoelectric (ME) fields, are distinguished by the power-flow vortices
and helicity parameters [E. O. Kamenetskii, R. Joffe, and R. Shavit, Phys. Rev.
E 87, 023201 (2013)]. These numerical studies can well explain recent
experimental results with MDM ferrite disks. In the present paper, we obtain
analytically topological characteristics of the ME-field modes. For this
purpose, we use a method of successive approximations. In the second
approximation we take into account the influence of the edge regions of an open
ferrite disk, which are excluded in the first-approximation solving of the
magnetostatic (MS) spectral problem. Based on the analytical method, we obtain
a 'pure' structure of the electric and magnetic fields outside the MDM ferrite
disk. The analytical studies can display some fundamental features that are
non-observable in the numerical results. While in numerical investigations, one
cannot separate the ME fields from the external electromagnetic (EM) radiation,
the present theoretical analysis allows clearly distinguish the eigen
topological structure of the ME fields. Importantly, this ME-field structure
gives evidence for certain phenomena that can be related to the Tellegen and
bianisotropic coupling effects. We discuss the question whether the MDM ferrite
disk can exhibit properties of the cross magnetoelectric polarizabilities.",1503.00270v2
2020-01-18,The sensitivity of the microstructure and properties to the peak temperature in an ultrafast heat treated low carbon-steel,"In this work, we investigate the sensitivity of the microstructure and
mechanical properties of an ultrafast heat treated low carbon-steel to the peak
temperature. In all studied cases, the steel was heated within the
intercritical temperature range (i.e. between the AC1 and AC3 temperatures).
Both the peak temperature and soaking time were varied, and their effect on the
size, the fraction of individual microstructural constituents and their tensile
mechanical response were investigated. It is shown that the increasing peak
temperature and soaking time promote austenite formation and recrystallization
processes in the ferritic matrix. The highest nanohardness is shown by
martensitic grains, while recovered ferrite demonstrated slightly higher
nanohardness compared to recrystallized ferrite. The applied heat treatment
parameters have strong effect on the nanohardness of martensite, whereas
nanohardness of ferrite microconstituents is not sensitive to variation of the
peak temperature and soaking time. The non-recrystallized ferrite is harder
than its recrystallized counterpart due to the higher dislocation density of
the former. Increasing peak temperatures promote strengthening in the material
at the expense of its ductility mainly due to increased martensite fraction.
The steel demonstrates enhanced strain hardening ability independently of the
peak temperature. Analysis of the experimental results showed that the
industrial processing window of +- 10 oC may lead to some heterogeneity of the
local microstructure in the ultrafast heat treated sheets. However, the latter
should not have any negative effect on the overall mechanical behavior of the
ultrafast heat treated steel sheets on the macro-scale.",2001.06713v1
2018-03-26,Enhancement of the magnetoelectric effect in multiferroic CoFe$_2$O$_4$/PZT bilayer by induced uniaxial magnetic anisotropy,"In this study we have compared magnetic, magnetostrictive and piezomagnetic
properties of isotropic and anisotropic cobalt ferrite pellets. The isotropic
sample was prepared by the ceramic method while the sample exhibiting uniaxial
anisotropy was made by reactive sintering using Spark Plasma Sintering (SPS).
This technique permits to induce a magnetic anisotropy in cobalt ferrite in the
direction of the applied pressure during SPS process. Sample with uniaxial
anisotropy revealed a higher longitudinal magnetostriction and piezomagnetism
compared to the isotropic sample, but the transversal magnetostriction and
piezomagnetism were dramatically reduced. In the case of magnetoelectric
layered composite, the magnetoelectric coefficient is directly related to the
sum of the longitudinal and transversal piezomagnetic coefficients. These two
coefficients being opposite in sign, the use of material exhibiting high
longitudinal and low transversal piezomagnetic coefficient (or vice versa) in
ME devices is expected to improve the ME effect. Hence, ME bilayer devices were
made using isotropic and anisotropic cobalt ferrite stuck with a PZT layer. ME
measurements at low frequencies revealed that bilayer with anisotropic cobalt
ferrite exhibits a ME coefficient three times higher than a bilayer with
isotropic cobalt ferrite. We also investigated the behavior of such composites
when excited at resonant frequency.",1803.09677v1
2023-09-18,Computational Exploration of Magnetic Saturation and Anisotropy Energy for Nonstoichiometric Ferrite Compositions,"A grand challenge in materials research is identifying the relationship
between composition and performance. Herein, we explore this relationship for
magnetic properties, specifically magnetic saturation (M$_s$) and magnetic
anisotropy energy (MAE) of ferrites. Ferrites are materials derived from
magnetite (which has the chemical formulae Fe$_3$O$_4$) that comprise metallic
elements in some combination such as Fe, Mn, Ni, Co, Cu and Zn. They are used
in a variety of applications such as electromagnetism, magnetic hyperthermia,
and magnetic imaging. Experimentally, synthesis and characterization of
magnetic materials is time consuming. In order to create insight to help guide
synthesis, we compute the relationship between ferrite composition and magnetic
properties using density functional theory (DFT). Specifically, we compute
M$_s$ and MAE for 571 ferrite structures with the formulae
M1$_x$M2$_y$Fe$_{3-x-y}$O$_4$, where M1 and M2 can be Mn, Ni, Co, Cu and/or Zn
and 0 $\le$ x $\le$ 1 and y = 1 - x. By varying composition, we were able to
vary calculated values of M$_s$ and MAE by up to 9.6$\times$10$^5$ A m$^{-1}$
and 14.1$\times$10$^5$ J m$^{-3}$, respectively. Our results suggest that
composition can be used to optimize magnetic properties for applications in
heating, imaging, and recording. This is mainly achieved by varying M$_s$, as
these applications are more sensitive to variation in M$_s$ than MAE.",2309.09754v1
1997-09-02,First Passage Times and Time-Temperature-Transformation curves for Martensites,"Martensites are long-lived nonequilibrium structures produced following a
quench across a solid state structural transition. In a recent paper (Phys.
Rev. Lett. 78, 2168 (1997)), we had described a mode-coupling theory for the
morphology and nucleation kinetics of the equilibrium ferrite phase and twinned
martensites. Here we calculate nucleation rates within a first-passage time
formalism, and derive the time-temperature-transformation (TTT) diagram of the
ferrite-martensite system for athermal and isothermal martensites. Empirically
obtained TTT curves are extensively used by metallurgists to design heat
treatment cycles in real materials.",9709022v1
2002-02-17,Faraday rotation and sensitivity of (100) bismuth-substituted ferrite garnet films,"We have investigated the Faraday rotation of in-plane magnetized bismuth -
substituted ferrite garnet films grown by liquid phase epitaxy on (100)
oriented gadolinium gallium garnet substrates. The Faraday spectra were
measured for photon energies between 1.7 - 2.6 eV. To interprete the spectra,
we use a model based on two electric dipole transitions, one tetrahedral and
one octahedral. Furthermore, the Faraday rotation sensitivity was measured at
2.3 eV, and found to be in good agreement with the theoretical predicitions. In
particular, we find that the sensitivity increases linearly with the bismuth
content and nonlinearly with the gallium content.",0202281v1
2003-07-12,"Magnetic and microwave properties of (Ni,Co)Fe2O4-ferroelectric and (La,Ca,Sr)MnO3-ferroelectric multilayer structures","Structural, magnetic and ferromagnetic resonance characterization studies
have been performed on lay-ered ferromagnetic-ferroelectric oxides that show
strong magnetoelectric coupling. The samples contained thick films of ferrites
or substituted lanthanum manganites for the ferromagnetic phase and lead
zirconate titanate for the ferroelectric phase, and were sintered high
temperatures. Results indicate defect free ferrites, but deterioration of
manganite parameters due to diffusion at the interface and accounts for poor
magnetoelectric coupling in manganite-PZT samples.",0307302v1
2004-09-01,Mesoscopic quantized properties of magnetic-dipolar-mode oscillations in disk ferromagnetic particles,"Magnetic dipolar mode or magnetostatic (MS) oscillations in ferrite samples
have the wavelength much smaller than the electromagnetic wavelength at the
same frequency and, at the same time, much larger than the exchange interaction
spin wavelength. This intermediate position between the electromagnetic and
spin wave (exchange interaction) processes reveals very special behaviors of
the geometrical effects. It was shown recently that magnetic dipolar mode
oscillations in a normally magnetized ferromagnetic disk are characterized by
discrete energy levels resulting from the structural confinement. In this
article we give results of the energy spectra in MS wave ferrite disks taking
into account nonhomogeneity of the internal DC magnetic field.",0409023v1
2005-05-30,Dynamical Symmetry Breaking in Quasistatic Magnetic Oscillations,"Recent microwave experiments demonstrate the anapole-moment and
magnetoelectric properties in quasi-2D ferrite particles with
magnetic-dipolar-wave oscillating spectra. The theory developed in this paper
shows that there are the macroscopically quantum topological effects. Quantum
coherence for macroscopic systems refers to circumstances when large numbers of
particles can collectively cooperate in a single quantum state. These effects
are rarely observed through macroscopic measurements because statistical
averaging over many states usually masks all evidence of quantum discreteness.
Magnetic-dipolar oscillating modes in normally magnetized ferrite disks
demonstrate properties of a Hamiltonian system. The purpose of this paper is to
show that because of the adiabatic motion process for such a Hamiltonian system
one has macroscopic quantum effects of symmetry breaking, magnetic currents,
and eigen electric moments.",0505717v1
2007-03-14,Phase Separation of Bismuth Ferrite into Magnetite under Voltage Stressing,"Micro-Raman studies show that under ~700 kV/cm of d.c. voltage stressing for
a few seconds, thin-film bismuth ferrite BiFeO3 phase separates into magnetite
Fe3O4. No evidence is found spectroscopically of hemite alpha-Fe2O3, maghemite
gamma-Fe2O3, or of Bi2O3. This relates to the controversy regarding the
magnitude of magnetization in BiFeO3.",0703388v1
2001-05-01,Rectangular microwave resonators with magnetic anisotropy. Mapping onto pseudo integrable rhombus,"The rectangular microwave resonator filed by a ferrite with uniaxial magnetic
anisotropy is considered. It is shown that this task can be reduced to an empty
rhombus resonator with vertex angle defined by external magnetic field provided
the magnetic anisotropy of the ferrite is strong. Therefore statistics of eigen
frequencies for TM modes is described by the Brody or semi-Poisson distribution
with some exceptional cases.",0105001v1
2004-02-11,Plane waves with negative phase velocity in Faraday chiral mediums,"The propagation of plane waves in a Faraday chiral medium is investigated.
Conditions for the phase velocity to be directed opposite to the direction of
power flow are derived for propagation in an arbitrary direction; simplified
conditions which apply to propagation parallel to the distinguished axis are
also established. These negative phase-velocity conditions are explored
numerically using a representative Faraday chiral medium, arising from the
homogenization of an isotropic chiral medium and a magnetically biased ferrite.
It is demonstrated that the phase velocity may be directed opposite to power
flow, provided that the gyrotropic parameter of the ferrite component medium is
sufficiently large compared with the corresponding nongyrotropic permeability
parameters.",0402057v1
2008-01-26,Magnetoelectric Control of Domain Walls in a Ferrite Garnet Film,"The effect of magnetic domain boundaries displacement induced by electric
field is observed in epitaxial ferrite garnet films (on substrates with the
(210) crystallographic orientation). The effect is odd with respect to the
electric field (the direction of wall displacement changes with the polarity of
the voltage) and even with respect to the magnetization in domains. The
inhomogeneous magnetoelectric interaction as a possible mechanism of the effect
is proposed.",0801.4073v1
2010-12-28,Transmission Electron Microscopy Studies on RF Sputtered Copper Ferrite Thin Films,"Copper ferrite thin films were rf sputtered at a power of 50W. The as
deposited films were annealed in air at 800{\deg}C and slow cooled. The
transmission electron microscope (TEM) studies were carried out on as deposited
as well as on slow cooled film. Significantly larger defect concentration,
including stacking faults, was observed in 50W as deposited films than the
films deposited at a higher rf power of 200W. The film annealed at 800{\deg}C
and then slow cooled showed an unusual grain growth upto 180nm for a film
thickness of ~240nm. These grains showed Kikuchi pattern.",1012.5743v1
2011-03-25,Temperature dependence of spin resonance in cobalt substituted NiZnCu ferrites,"Cobalt substitutions were investigated in Ni0.4Zn0.4Cu0.2Fe2O4 ferrites,
initial complex permeability was then measured from 1 MHz to 1 GHz. It appears
that cobalt substitution led to a decrease in the permeability and an increase
in the \mus\timesfr factor. As well, it gave to the permeability spectrum a
sharp resonance character. We also observed a spin reorientation occurring at a
temperature depending on the cobalt content. Study of the complex permeability
versus temperature highlighted that the most resonant character was obtained at
this temperature. This shows that cobalt contribution to second order
magnetocrystalline anisotropy plays a leading role at this temperature.",1103.5024v1
2013-04-26,Ferroelectricity from iron valence ordering in rare earth ferrites?,"The possibility of multiferroicity arising from charge ordering in LuFe2O4
and structurally related rare earth ferrites is reviewed. Recent experimental
work on macroscopic indications of ferroelectricity and microscopic
determination of coupled spin and charge order indicates that this scenario
does not hold. Understanding the origin of the experimentally observed charge
and spin order will require further theoretical work. Other aspects of recent
research in these materials, such as geometrical frustration effects, possible
electric-field-induced transitions, or orbital order are also briefly treated.",1304.7255v1
2014-07-07,"Multiferroic hexagonal ferrites (h-RFeO$_3$, R=Y, Dy-Lu): an experimental review","Hexagonal ferrites (h-RFeO$_3$, R=Y, Dy-Lu) have recently been identified as
a new family of multiferroic complex oxides.
  The coexisting spontaneous electric and magnetic polarizations make
h-RFeO$_3$ rare-case ferroelectric ferromagnets at low temperature.
  Plus the room-temperature multiferroicity and predicted magnetoelectric
effect, h-RFeO$_3$ are promising materials for multiferroic applications.
  Here we review the structural, ferroelectric, magnetic, and magnetoelectric
properties of h-RFeO$_3$.
  The thin film growth is also discussed because it is critical in making high
quality single crystalline materials for studying intrinsic properties.",1407.1798v1
2015-01-29,Chiral-field microwave antennas (Chiral microwave near fields for far-field radiation),"In a single-element structure we obtain a radiation pattern with a squint due
to chiral microwave near fields originated from a magnetostatic-mode ferrite
disk. At the magnetostatic resonances, one has strong subwavelength
localization of energy of microwave radiation. Magnetostatic oscillations in a
thin ferrite disk are characterized by unique topological properties: the
Poynting-vector vortices and the field helicity. The chiral-topology near
fields allow obtaining unique phase structure distribution for far-field
microwave radiation.",1501.07387v1
2015-07-21,Frequency-dependent effective permeability tensor of unsaturated polycrystalline ferrites,"Frequency-dependent permeability tensor for unsaturated polycrystalline
ferrites is derived through an effective medium approximation that combines
both domain-wall motion and rotation of domains in a single consistent
scattering framework. Thus derived permeability tensor is averaged on a
distribution function of the free energy that encodes paramagnetic states for
anhysteretic loops. The initial permeability is computed and frequency spectra
are given by varying macroscopic remanent field.",1507.05814v1
2016-11-03,Room temperature multiferroism in polycrystalline thin films of gallium ferrite,"Sol-gel deposited (010) textured polycrystalline thin films of gallium
ferrite (GaFeO3 or GFO) on n-Si(100) and Pt/Si(111) substrates are
characterized for room temperature multiferroism. Structural characterization
using X-ray diffraction and Raman spectroscopy confirms formation of single
phase with nano-sized crystallites. Temperature dependent magnetization study
demonstrates ferri to paramagnetic transition at ~300 K. Room temperature
piezoresponse force microscopic analysis reveals local 180 degree phase
switching of ferroelectric domains at very high coercive field EC, ~ 1350 kV/cm
consistent with recent experimental and first-principles studies. Our study
opens up possibility of integrating polycrystalline GFO in novel room
temperature multiferroic devices.",1611.01128v1
2012-04-13,Spin Glass-like Phase below ~ 210 K in Magnetoelectric Gallium Ferrite,"In this letter we show the presence of a spin-glass like phase in single
crystals of magnetoelectric gallium ferrite (GaFeO3) below ~210 K via
temperature dependent ac and dc magnetization studies. Analysis of frequency
dispersion of the susceptibility peak at ~210 K using the critical slowing down
model and Vogel-Fulcher law strongly suggests the existence of a classical
spin-glass like phase. This classical spin glass behavior of GaFeO3 is
understood in terms of an outcome of geometrical frustration arising from the
inherent site disorder among the antiferromagnetically coupled Fe ions located
at octahedral Ga and Fe sites.",1204.2973v1
2015-12-24,Polaritons dispersion in a composite ferrite-semiconductor structure near gyrotropic-nihility state,"In the context of polaritons in a ferrite-semiconductor structure which is
influenced by an external static magnetic field, the gyrotropic-nihility can be
identified from the dispersion equation related to bulk polaritons as a
particular extreme state, at which the longitudinal component of the
corresponding constitutive tensor and bulk constant simultaneously acquire
zero. Near the frequency of the gyrotropic-nihility state, the conditions of
branches merging of bulk polaritons, as well as an anomalous dispersion of bulk
and surface polaritons are found and discussed.",1512.07870v2
2019-07-08,Effect of elasto-plastic compatibility of grains on the void initiation criteria in low carbon steel,"The present study evidences the role of ferrite grain size distributions on
the occurrence of void initiation in a low carbon steel. Various
thermomechanical treatments were done to create ultrafine, bimodal and coarse
range of ferrite grain distributions. A two parameter characterization of
probable void initiation sites is proposed; elastic modulus difference and
difference in Schmid factor of the grains surrounding the void. All
microstructures were categorized based on the ability to ease or resist void
nucleation. For coarse grains, elastic modulus difference as well as the Schmid
factor difference is highest, intermediate for ultrafine and lowest for bimodal
microstructure.",1907.03703v1
2021-01-28,Prediction of new low-energy phases of BiFeO$_3$ with large unit cell and complex tilts beyond Glazer notation,"Bismuth ferrite is one of the most widely studied multiferroic materials
because of its large ferroelectric polarisation coexisting with magnetic order
at room temperature. Using density functional theory (DFT), we identify several
previously unknown polar and non-polar structures within the low-energy phase
space of perovskite-structure bismuth ferrite, BiFeO$_3$. Of particular
interest is a series of non-centrosymmetric structures with polarisation along
one lattice vector, combined with anti-polar distortions, reminiscent of
ferroelectric domains, along a perpendicular direction. We discuss possible
routes to stabilising the new phases using biaxial heteroepitaxial strain or
interfacial electrostatic control in heterostructures.",2101.12114v1
2019-03-22,Spin-wave coupling to electromagnetic cavity fields in dysposium ferrite,"Coupling of spin-waves with electromagnetic cavity field is demonstrated in
an antiferromagnet, dysprosium ferrite (DyFeO3). By measuring transmission at
0.2-0.35 THz and sweeping sample temperature, magnon-photon coupling signatures
were found at crossings of spin-wave resonances with Fabry-Perot cavity modes
formed in samples. The obtained spectra are explained in terms of classical
electrodynamics and a microscopic model.",1903.09590v2
2019-11-07,Magnetic monopoles and toroidal moments in LuFeO$_3$ and related compounds,"Magnetic monopoles and toroidal order are compelling features that have long
been theorized but remain elusive in real materials. Multiferroic hexagonal
ferrites are an interesting realization of frustrated triangular lattice, where
magnetic order is coupled to ferroelectricity and trimerization. Here we
propose a mechanism, through which magnetic monopolar and toroidal orders
emerge from the combination of 120$^\circ$ antiferromagnetism and
trimerization, present in hexagonal manganites and ferrites. The experimentally
observable signatures of magnetic monopolar and toroidal orders are identified
in the inelastic neutron scattering cross section, simulated from a microscopic
model of LuFeO3. The non-reciprocal magnon propagation is demonstrated.",1911.02704v1
2020-08-31,A collection of definitions and fundamentals for a design-oriented inductor model,"This paper defines and develops useful concepts related to the several kinds
of inductances employed in any comprehensive design-oriented ferrite-based
inductor model, which is required to properly design and control high-frequency
operated electronic power converters. It is also shown how to extract the
necessary parameters from a ferrite material datasheet in order to get inductor
models useful for a wide range of core temperatures and magnetic induction
levels.",2008.13634v3
2004-01-24,Dielectric and Pyroelectric Properties of Thick Film Ferromagnetic - Piezoelectric Structures,"Layered ferromagnetic-piezoelectric composites show mechanical strain
mediated electromagnetic coupling. Here we discuss dielectric and piezoelectric
properties of ferrite-lead zirconate titanate (PZT) and lanthanum manganite-PZT
samples. Results of our investigations on dielectric and pyroelectric
properties of multilayer ferromagnetic-piezoelectric are presented here. Lead
zircinate-titanate PbZrxTi1-xO3 (PZT) was used for the piezoelectric phase in
all the structures. The following materials were used for the ferromagnetic
component: nickel-zinc ferrites Ni0.9Zn 0.1Fe2O4 (NFO1) and Ni0.8Zn0.2Fe2O4
(NFO2), cobalt ferrite (CFO), lithium ferrite (LFO), lanthanum strontium
manganite La0.7Sr0.3MnO3 (LSM), and lanthanum-calcium manganite La0.7Ca0.3MnO3
(LCM). The pyroelectric effect was studied by measuring the current J flowing
through a closed loop containing the sample and an electrometer as the sample
temperature T was slowly varied at the rate 0.1 K/s. Polarized PZT layers
generate a pyroelectric current as the temperature changes. The main indicator
of pyroelectric nature of the current is the sign reversal when the thermal
cycle is switched from heating to cooling. Almost all of the multilayer
structures showed a pyroelectric current, but the pyroelectric coefficient
varied in a wide range. (i) For NFO1-PZT system the coefficient was in the
range 0.01 - 10 nC/(cm2 K), depending on the temperature. (ii) CFO-PZT and
LFO-PZT structures showed a large thermal current and a weak pyroelectric
effect. (iii) Thermal currents, however, were absent in LCM-PZT within the
temperature range from the room temperature to 400 K. (iv) In LSM-PZT, the
thermal current exceeded the pyroelectric current. A model is proposed for an
understanding of these results.",0401481v1
2005-07-13,Colossal Spin-Phonon Anomalies and the Ferroelectric Phase Transition in the Model Multiferroic Bifeo3,"We report a temperature-dependent Raman and neutron scattering investigation
of the multiferroic material bismuth ferrite BiFeO3 (BFO).",0507291v1
2013-11-25,Structural and Dielectric Characterization on Multiferroic xNi0.9Zn0.1Fe2O4/(1-x)PbZr0.52Ti0.48O3 Particulate Composite,"We have carried out the powder x-ray diffraction and dielectric studies on
multiferroic particulate composite xNi0.9Zn0.1Fe2O4/(1-x)PbZr0.52Ti0.48O3 with
x=0.15, 0.30, 0.45, 0.60, 0.75 and 0.90 to explore the structural and
ferroelectric properties. A conventional double sintering method was used to
prepare the xNi0.9Zn0.1Fe2O4/(1-x)PbZr0.52Ti0.48O3 composites. The structure of
one of the component Ni0.9Zn0.1Fe2O4 is spinel cubic with space group Fd3m,
while the other component PbZr0.52Ti0.48O3 is selected around the morphotropic
phase boundary region in which the tetragonal and monoclinic phases with space
group P4mm and Cm coexist respectively. We have carried out Rietveld refinement
of the structure to check the formation of ideal composites with separate
ferroelectric and ferrite phases. Even though the structural characterization
does not reveal the formation of any new phase due to reaction between the two
components of the composite during sintering, the tetragonality of the
PbZr0.52Ti0.48O3 continuously decreases with increasing the ferrite fraction
while the lattice parameter of ferrite phase increases with increasing fraction
of the ferroelectric phase. Similarly, the dielectric study reveals clear shift
in the ferroelectric to paraelectric phase transition temperature of
PbZr0.52Ti0.48O3 during composite formation suggesting that part of Ni2+, Zn2+/
Fe3+ ions are diffusing at the B-site of PbZr0.52Ti0.48O3 replacing Ti4+, which
in turn decreases its transition temperature. Scanning electron micrograph of
sintered pellet surface confirms the presence of two types of particle
morphology in the particulate composite, corresponding to ferrite and
ferroelectric phases.",1311.6217v2
2016-10-08,Enhancement of Impedance by Chromium Substitution and Correlation with DC Resistivity in Cobalt Ferrite,"Chromium substituted cobalt ferrite with grain size less than the single
domain (approx. 70 nm) has been prepared by the sol-gel method. XRD analysis
reveals that the samples crystallize to cubic symmetry with spacegroup number
227. Two transition temperatures (TD (approx. 450 K) and TM (approx. 600 K)
have been observed from the impedance verses temperature measurement. TD
increases with the increase in frequency due to dipole response to the
frequency. TM is comparable with the para-ferrimagnetic transition temperature
of cobalt ferrite, which is independent of frequency. This result is well
supported by the temperature dependent DC conductivity measurement. The
modified Debye relaxation could be explained the impedance spectra of
CoFe2-xCrxO4. The grain and grain boundary effect on impedance spectroscopy has
been observed from Cole-Cole analysis. The ac conductivity follows Arrhenius
behavior at different frequencies. All the samples exhibit the negative
temperature coefficient of resistance behavior which reveals the semiconducting
behavior of the material. The Mott VRH model could explain the DC electrical
conductivity. Both ac impedance and DC resistivity are well co-related each
other to explain the electron transport properties in Cr substituted cobalt
ferrite. The electrical transport properties could be explained by the electron
hopping between different metal ions via oxygen in the material.",1610.02489v1
2020-07-01,"Impact of V substitution on the physical properties of Ni-Zn-Co ferrites: structural, magnetic, dielectric and electrical properties","We have investigated the Vanadium- (V) substituted Ni-Zn-Co ferrites where
the samples were prepared using solid-state reaction technique. The impact of
V5+ substitution on the structural, magnetic, dielectric and electrical
properties of Ni-Zn-Co ferrites has been studied. XRD analysis confirmed the
formation of a single-phase cubic spinel structure. The lattice constants have
been calculated both theoretically and experimentally along with other
structural parameters such as bulk density, X-ray density and porosity. The
FESEM images are taken to study the surface morphology. FTIR measurement is
also performed which confirms spinel structure formation. The saturation
magnetization (Ms), coercive field (Hc) and Bohr magneton (B) were calculated
from the obtained M-H loops. The temperature dependent permeability is studied
to obtain the Curie temperature. Frequency and composition dependence of
permeability was also analyzed. Dielectric behavior and ac resistivity are also
subjected to investigate the frequency dependency. An inverse relationship was
observed between the composition dependence of dielectric constant and ac
resistivity. The obtained results such as the electrical resistivity,
dielectric constants and magnetic properties suggest the appropriateness of the
studied ferrites in microwave device applications.",2007.00602v1
2019-10-30,Coherent x-ray radiation induced by high-current breakdown on a ferrite surface,"We for the first time observe that at the initial stage of a high-current
discharge, a low-divergence short (< 2 ns) electromagnetic pulse is formed over
a ferrite surface. The 50% part of this pulse lies in the region of fairly hard
x-ray radiation (photon energy >1 keV) with the energy $\approx$0.6 mJ and the
average power 0.3 MW. The radiation propagates parallel to the surface in the
anode direction with the angle divergence < 2$^{o}$. The high directionality of
the radiation in absence of the aperture-limiting devices for the radiation
beam and the quadratic dependence of the spatial radiation energy flux density
on the active part of the ferrite prism points to the coherent nature of the
observed radiation. A possible generation mechanism of the radiation is
proposed. It is based on the short-lived magnetization of the unit areas on the
ferrite surface by a high-power electromagnetic pulse and subsequent coherent
interference of the unit waves irradiated by these areas.",1910.13851v2
2020-01-03,Synthesis and characterization of Zn doped Mn ferrites nanostructures,"Zn doped Mn ferrites nanoparticles were fabricated by using Co-precipitation.
Variation in structure, magnetic and optical properties of MnZn ferrites has
been discussed. First of all, samples were synthesized, annealed at different
temperatures and then characterized. The as-synthesized and annealed samples
were investigated by X-ray diffraction (XRD), Scanning electron microscopy
(SEM), Energy Dispersive spectroscopy (EDX), Ultra Violet visible spectrometry
(Uv-Vis spectrometry) and Vibrating sample magnetometer (VSM). The average
crystallite size of MnZn ferrites nanoparticles determined from XRD were in the
range of 42 to 60 nm. These nanoparticles possess normal spinel structure. The
SEM images showed the physical shape of the samples, which showed that the as
prepared samples are more agglomerated and having flake like shape rather than
annealed at 700C while the samples have longitudinal or rod like shape on
annealing at 700C. The coercivity (Hc), saturation magnetization (Ms), and
remanence (Mr) of Nps were also calculated. The (Ms) value is increasing from
26 to 65 emu/g, the coercivity (Hc) is varying from 13 to 193 Oe and remanence
(Mr) has also showing increasing trend although very less, from 0.031 to 0.798
emu/g which are a little part of their bulk counter parts. The band gap energy
of the samples was showing decreasing trend as with the increase of particle
size which is of the order of 3.5 to 2.9 eV.",2001.00741v1
2020-09-17,Magnetoelectric near fields,"We consider near field topological singularities originated from magnetic
dipolar mode oscillations in ferrite disk particles.",2009.08084v1
2022-11-02,Solar energy harvesting in magnetoelectric coupled manganese ferrite nanoparticles incorporated nanocomposite polymer films,"Poly(vinylidenefluoride-co-trifluoroethylene) (P(VDF-TrFE)) based
pyroelectric as well as magnetoelectric materials offer great promises for
energy harvesting for flexible and wearable applications. Hence, this work
focus on solar energy harvesting as well as magnetoelectric phenomenon in two
phase nanocomposite film where the constituting phases are manganese ferrite
(MnFe2O4) nanoparticles and P(VDF-TrFE) polymer. Composite films have been
prepared using solution casting technique. X-ray diffraction result shows
higher crystallinity of these films. The ferroelectric, magnetic and
magnetoelectric properties in variation with applied field and volume
percentage of ferrite nanoparticles have been investigated. The preparation
condition was optimized in such a way that it results improved ferroelectric
polarization of nanocomposite film after incorporation of small amount of
ferrite nanoparticles. The maximum magnetoelectric-coupling coefficient of
about 156 mV/Oe-Cm was obtained for optimum nanocomposite film when DC bias
field was applied perpendicular to electric polarization direction. From a
pyroelectric device perspective, solar energy harvesting is also reported. An
open circuit voltage of 5V and short circuit current of order of ~1 nA is
demonstrated without any pre amplification. Hence, the combination of
magnetoelectric and pyroelectric properties of nanocomposite film presented
here indicate as a perfect candidate for smart materials, spintronics devices
and specified magnetoelectric-based applications.",2211.01007v2
2023-03-30,Towards Quantitative Analysis of Deuterium Absorption in Ferrite and Austenite during Electrochemical Charging by Comparing Cyclic Voltammetry and Cryogenic Transfer Atom Probe Tomography,"Hydrogen embrittlement mechanisms of steels have been studied for several
decades. Understanding hydrogen diffusion behavior in steels is crucial towards
both developing predictive models for hydrogen embrittlement and identifying
mitigation strategies. However, because hydrogen has a low atomic mass, it is
extremely challenging to detect by most analytical methods. In recent years,
cryogenic-transfer atom probe tomography (APT) of
electrochemically-deuterium-charged steels has provided invaluable qualitative
analysis of nanoscale deuterium traps such as carbides, dislocations, grain
boundaries and interfaces between ferrite and cementite. Independently, cyclic
voltammetry (CV) has provided valuable analysis of bulk hydrogen diffusion in
steels. In this work, we use a combination of CV and cryogenic-transfer APT for
quantitative analysis of deuterium pickup in electrolytically charged pure Fe
(ferrite) and a model austenitic Fe18Cr14Ni alloy without any second phase or
defect trap sites. The high solubility and low diffusivity of hydrogen in
austenite versus ferrite are highlighted to result in clear observable
signatures in CV and cryogenic-transfer APT results. The remaining challenges
and pathway for enabling quantitative analysis of hydrogen pick up in steels is
also discussed.",2303.17070v1
2023-09-24,FeCo Nanowire-Strontium Ferrite Powder Composites for Permanent Magnets with High-Energy Products,"Due to the issues associated with rare-earth elements, there arises a strong
need for magnets with properties between those of ferrites and rare-earth
magnets that could substitute the latter in selected applications. Here, we
produce a high remanent magnetization composite bonded magnet by mixing FeCo
nanowire powders with hexaferrite particles. In the first step, metallic
nanowires with diameters between 30 and 100 nm and length of at least 2 {\mu}m
are fabricated by electrodeposition. The oriented as-synthesized nanowires show
remanence ratios above 0.76 and coercivities above 199 kA/m and resist core
oxidation up to 300 {\deg}C due to the existence of a > 8 nm thin oxide
passivating shell. In the second step, a composite powder is fabricated by
mixing the nanowires with hexaferrite particles. After the optimal nanowire
diameter and composite composition are selected, a bonded magnet is produced.
The resulting magnet presents a 20% increase in remanence and an enhancement of
the energy product of 48% with respect to a pure hexaferrite (strontium
ferrite) magnet. These results put nanowire-ferrite composites at the forefront
as candidate materials for alternative magnets for substitution of rare earths
in applications that operate with moderate magnet performance.",2309.13724v1
2024-02-21,Discrete slip plane analysis of ferrite microtensile tests: On the influence of dislocation source distribution and non-Schmid effects on slip system activity,"The slip system activity in microtensile tests of ferrite single crystals is
compared with predictions made by the discrete slip plane model proposed by
Wijnen et al. (International Journal of Solids and Structures 228, 111094,
2021). This is an extension of conventional crystal plasticity in which the
stochastics and physics of dislocation sources are taken into account in a
discrete slip band. This results in discrete slip traces and non-deterministic
mechanical behavior, similar to what is observed in experiments. A detailed
analysis of which slip systems are presumed to be active in experiments is
performed. In small-scale mechanical tests on BCC metals and alloys, non-Schmid
effects are often needed to explain the observed response. Therefore, these
effects are incorporated into the model by extending a non-Schmid framework
commonly used to model {110} slip to {112} planes. The slip activity in the
simulations is compared to the slip activity in single crystal ferrite
microtensile tests. This is done for the discrete slip plane model with and
without non-Schmid effects, as well as for a conventional crystal plasticity
model. The conventional crystal plasticity model fails to predict the diversity
in active slip systems that is observed experimentally. The slip activity
obtained with the discrete slip plane model is in convincingly better agreement
with the experiments. Including non-Schmid effects only entails minor
differences. This suggests that stochastic effects dominate the behavior of
ferrite crystals with dimensions in the order of a few micrometers and that
non-Schmid effects may not play a large role.",2402.14168v1
2003-07-23,Dynamic Magnetoelectric Effects in Bulk and Layered composites of Cobalt Zinc Ferrite and Lead Zirconate Titanate,"Low frequency magnetoelectric (ME) coupling has been investigated in bulk and
multilayers of cobalt zinc ferrite, Co1-xZnxFe2O4 (x=0-0.6), and lead zirconate
titanate. In bulk samples, the transverse and longitudinal couplings are weak
and are of equal magnitude. A substantial strengthening of ME interactions is
evident in layered structures, with the ME voltage coefficient a factor of
10-30 higher than in bulk samples. Important findings of the studies in layered
composites are as follows. (i) The transverse coupling is stronger than the
longitudinal coupling. (ii) The strength of ME interactions is dependent on Zn
substitution with a maximum for x=0.4. (iii) Analysis of volume and static
magnetic field dependence of ME voltage coefficients reveal a weak coupling at
the ferromagnetic-piezoelectric interface. (iv) The interface coupling k
increases with Zn substitution and k versus x profile shows a maximum centered
at x=0.4. (iv) The Zn-assisted enhancement is attributed to efficient
magneto-mechanical coupling in the ferrite.",0307597v1
2006-06-24,Synthesis and Magnetic Properties of Cobalt Ferrite (CoFe2O4) Nanoparticles Prepared by Wet Chemical Route,"Magnetic nanoparticles of cobalt ferrite have been synthesized by wet
chemical method using stable ferric and cobalt salts with oleic acid as the
surfactant. X-ray Diffraction (XRD) and Transmission Electron Microscope (TEM)
confirmed the formation of single phase cobalt ferrite nanoparticles in the
range 15-48nm depending on the annealing temperature and time. The size of the
particles increases with annealing temperature and time while the coercivity
goes through a maximum, peaking at around 28nm. A very large coercivity
(10.5kOe) is observed on cooling down to 77K while typical blocking effects are
observed below about 260K. The high field moment is observed to be small for
smaller particles and approaches the bulk value for large particles.",0606631v2
2006-07-03,Interaction between superconducting vortices and Bloch wall in ferrite garnet film,"Interaction between a Bloch wall in a ferrite-garnet film and a vortex in a
superconductor is analyzed in the London approximation. Equilibrium
distribution of vortices formed around the Bloch wall is calculated. The
results agree quantitatively with magneto-optical experiment where an in-plane
magnetized ferrite-garnet film placed on top of NbSe2 superconductor allows
observation of individual vortices. In particular, our model can reproduce a
counter-intuitive attraction observed between vortices and a Bloch wall having
the opposite polarity. It is explained by magnetic charges appearing due to
discontinuity of the in-plane magnetization across the wall.",0607043v2
2007-02-14,Vortices and chirality of magnetostatic modes in quasi-2D ferrite disk particles,"In this paper we show that the vortex states can be created not only in
magnetically soft ""small"" (with the dipolar and exchange energy competition)
cylindrical dots, but also in magnetically saturated ""big"" (when the exchange
is neglected) cylindrical dots. A property associated with a vortex structure
becomes evident from an analysis of confinement phenomena of magnetic
oscillations in a ferrite disk with a dominating role of magnetic-dipolar
(non-exchange-interaction) spectra. In this case the scalar
(magnetostatic-potential) wave functions may have a phase singularity in a
center of a dot. A non-zero azimuth component of the flow velocity demonstrates
the vortex structure. The vortices are guaranteed by the chiral edge states of
magnetic-dipolar modes in a quasi-2D ferrite disk.",0702327v1
2007-03-11,A low-noise ferrite magnetic shield,"Ferrite materials provide magnetic shielding performance similar to commonly
used high permeability metals but have lower intrinsic magnetic noise generated
by thermal Johnson currents due to their high electrical resistivity.
Measurements inside a ferrite shield with a spin-exchange relaxation-free
atomic magnetometer reveal a noise level of 0.75 fT Hz^(-1/2), 25 times lower
than what would be expected in a comparable mu-metal shield. The authors
identify a 1/f component of the magnetic noise due to magnetization
fluctuations and derive general relationships for the Johnson current noise and
magnetization noise in cylindrical ferromagnetic shields in terms of their
conductivity and complex magnetic permeability.",0703115v2
2007-07-09,"Effective chiral magnetic currents, topological magnetic charges, and microwave vortices in a cavity with an enclosed ferrite disk","In microwaves, a TE-polarized rectangular-waveguide resonator with an
inserted thin ferrite disk gives an example of a nonintegrable system. The
interplay of reflection and transmission at the disk interfaces together with
the material gyrotropy effect gives rise to whirlpool-like electromagnetic
vortices in the proximity of the ferromagnetic resonance. Based on numerical
simulation, we show that a character of microwave vortices in a cavity can be
analyzed by means of consideration of equivalent magnetic currents. Maxwell
equations allows introduction of a magnetic current as a source of the
electromagnetic field. Specifically, we found that in such nonintegrable
structures, magnetic gyrotropy and geometrical factors leads to the effect of
symmetry breaking resulting in effective chiral magnetic currents and
topological magnetic charges. As an intriguing fact, one can observe precessing
behavior of the electric-dipole polarization inside a ferrite disk.",0707.1216v1
2007-07-09,Microwave whirlpools in a rectangular-waveguide cavity with a thin ferrite disk,"We study a three dimensional system of a rectangular-waveguide resonator with
an inserted thin ferrite disk. The interplay of reflection and transmission at
the disk interfaces together with material gyrotropy effect, gives rise to a
rich variety of wave phenomena. We analyze the wave propagation based on full
Maxwell-equation numerical solutions of the problem. We show that the
power-flow lines of the microwave-cavity field interacting with a ferrite disk,
in the proximity of its ferromagnetic resonance, form whirlpool-like
electromagnetic vortices. Such vortices are characterized by the dynamical
symmetry breaking. The role of ohmic losses in waveguide walls and dielectric
and magnetic losses in a disk is a subject of our investigations.",0707.1236v1
2008-04-10,Eigen power-flow-density vortices of magnetostatic modes in thin ferrite disks,"In confined magnetically ordered structures one can observe vortices of
magnetization and electromagnetic power flow vortices. There are topologically
distinct and robust states. In this paper we show that in a normally magnetized
quasi-2D ferrite disk there exist eigen power-flow-density vortices of
magnetic-dipolar-mode oscillations. Because of such circular power flows, the
oscillating modes are characterized by stable magnetostatic energy states and
discrete angular moments of the wave fields. We show that the
power-flow-density vortices of magnetostatic modes can be excited by
electromagnetic fields of a microwave cavity. There is a clear correspondence
between the power-flow-density vortex structures in a ferrite disk derived from
an analytical solution of the magnetostatic-wave spectral problem and obtained
by the numerical-simulation electromagnetic program.",0804.1666v1
2009-08-24,"Spinel ferrite nanocrystals embedded inside ZnO: magnetic, electronic and magneto-transport properties","In this paper we show that spinel ferrite nanocrystals (NiFe2O4, and CoFe2O4)
can be texturally embedded inside a ZnO matrix by ion implantation and
post-annealing. The two kinds of ferrites show different magnetic properties,
e.g. coercivity and magnetization. Anomalous Hall effect and positive
magnetoresistance have been observed. Our study suggests a
ferrimagnet/semiconductor hybrid system for potential applications in
magneto-electronics. This hybrid system can be tuned by selecting different
transition metal ions (from Mn to Zn) to obtain various magnetic and electronic
properties.",0908.3488v1
2009-11-22,Electronic structure and magnetic properties of Ni0.2Cd0.3Fe2.5-xAlxO4 (x = 0.0 - 0.4) ferrite nanoparticles,"Structural, magnetic and electronic structural properties of
Ni0.2Cd0.3Fe2.5-xAlxO4 ferrites nanoparticles have been studied x-ray
diffraction (XRD), transmission electron microscopy (TEM), dc magnetization,
and near edge x-ray absorption fine structure spectroscopy (NEXAFS)
measurements. Nanoparticles of Ni0.2Cd0.3Fe2.5-xAlxO4 (x = 0.0 - 0.4) ferrite
were synthesized using sol-gel method. The XRD and TEM measurements show that
all samples have single phase nature with cubic structure and have
nanocrystalline behavior. From the XRD and TEM analysis, it is observed that
particle size increases with Al doping. DC magnetization measurements infer
that magnetic moment decreases whereas blocking temperature increases with
increase in Al doping. It is observed that the magnetic moment decreases with
Al doping which may be due to the dilution of the sublattice by the doping of
Al ions. The NEXAFS measurements performed at room temperature indicates that
Fe exist in mixed valence state.",0911.4227v1
2010-06-07,A Robust Approach for the Growth of Epitaxial Spinel Ferrite Films,"Heteroepitaxial spinel ferrites NiFe2O4 and CoFe2O4 films have been prepared
by pulsed laser deposition (PLD) at various temperatures (175 - 690 {\deg}C)
under ozone/oxygen pressure of 10 mTorr. Due to enhanced kinetic energy of
ablated species at low pressure and enhanced oxidation power of ozone, epitaxy
has been achieved at significantly lower temperatures than previously reported.
Films grown at temperature below 550 {\deg}C show a novel growth mode, which we
term ""vertical step-flow"" growth mode. Epitaxial spinel ferrite films with
atomically flat surface over large areas and enhanced magnetic moment can be
routinely obtained. Interestingly, the growth mode is independent of the nature
of substrates (spinel MgAl2O4, perovskite SrTiO3, and rock salt MgO) and film
thicknesses. The underlying growth mechanism is discussed.",1006.1161v1
2011-02-21,Contributions of Al and Ni segregation to the interfacial cohesion of Cu-rich precipitates in ferritic steels,"We characterise the influence of the segregation behaviours of two typical
alloying elements, aluminium and nickel, on the interfacial cohesive properties
of copper-rich precipitates in ferritic steels, with a view towards
understanding steel embrittlement. The first-principles method is used to
compute the energetic and bonding properties of aluminium and nickel at the
interfaces of the precipitates and corresponding fracture surfaces. Our results
show the segregation of aluminium and nickel at interfaces of precipitates are
both energetically favourable. We find that the interfacial cohesion of copper
precipitates is enhanced by aluminium segregation but reduced by nickel
segregation. Opposite roles can be attributed to the different symmetrical
features of the valence states for aluminium and nickel. The nickel-induced
interfacial embrittlement of copper-rich precipitates increase the
ductile-brittle transition temperature (DBTT) of ferritic steels and provides
an explanation of many experimental phenomena, such as the fact that the shifts
of DBTT of reactor pressure vessel steels depend the copper and nickel content.",1102.4234v2
2011-03-29,Probing Magnetoelastic Coupling and Structural Changes in Magnetoelectric Gallium Ferrite,"Temperature dependent X-ray diffraction and Raman spectroscopic studies were
carried out on the flux grown single crystals of gallium ferrite with Ga:Fe
ratio of 0.9:1.1. Site occupancy calculations from the Rietveld refinement of
the X-ray data led to the estimated magnetic moment of ~0.60 \muB /f.u. which
was in good agreement with the experimental data. Combination of these two
measurements indicates that there is no structural phase transition in the
material between 18 K to 700 K. A detailed line shape analysis of the Raman
mode at ~375 cm^-1 revealed a discontinuity in the peak position data
indicating the presence of spin-phonon coupling in gallium ferrite. A
correlation of the peak frequency with the magnetization data led to two
distinct regions across a temperature ~180 K with appreciable change in the
spin-phonon coupling strength from ~ 0.9 cm^-1 (T < 180 K) to 0.12 cm-1 (180 K
< T < Tc). This abrupt change in the coupling strength at ~180 K strongly
suggests an altered spin dynamics across this temperature.",1103.5541v2
2011-03-30,Analysis of volume distribution of power loss in ferrite cores,"We present a technique to estimate the inhomogeneities of magnetic loss
across the section of ferrite cores under ac excitation. The technique is based
on two distinct calorimetric methods that we presented elsewhere. Both methods
are based on the measurement of the rate of increase of the sample temperature
under adiabatic condition. The temperature ramp is recorded either measuring
the sample bulk resistivity or using a platinum probe pasted on the sample
surface. As an example we apply the procedure to an industrial sample of Mn-Zn
ferrite under controlled sinusoidal excitation with a peak induction of 50 mT
in the range between 100 kHz and 2 MHz. The results are discussed by comparison
with simulations of the dissipation field profile through the sample,
calculated using a finite element method (FEM) code.",1103.5839v1
2011-06-07,Effect of Zn substitution on morphology and magnetic properties of copper ferrite nanofibers,"Spinel ferrite Cu1-xZnxFe2O4 nanofibers over a compositional range 0 < x < 1
were prepared by electrospinning combined with sol-gel method. The influence of
Zn2+ ions substitution on morphology, structure, and magnetic properties of
copper ferrite has been investigated. The results show that surface of CuFe2O4
nanofibers consists of small open porosity, while surface of doped nanofibers
reveals smooth and densified nature. With increasing Zn substitution,
saturation magnetization initially increases and then decreases with a maximum
value of 58.4 emu/g at x = 0.4, coercivity and square ratio all decrease. The
influence of substitution on magnetic properties is related with the cation
distraction and exchange interactions between spinel lattices.",1106.1269v1
2011-08-11,Thermoelectric Spin-Transfer Torque MRAM with Sub-Nanosecond Bi-Directional Writing using Magnonic Current,"A new genre of Spin-Transfer Torque (STT) MRAM is proposed, in which
bi-directional writing is achieved using thermoelectrically controlled magnonic
current as an alternative to conventional electric current. The device uses a
magnetic tunnel junction (MTJ), which is adjacent to a non-magnetic metallic
and a ferrite film. This film stack is heated or cooled by a Peltier element
which creates a bi-directional magnonic pulse in the ferrite film. Conversion
of magnons to spin current occurs at the ferrite-metal interface, and the
resulting spin-transfer torque is used to achieve sub-nanosecond precessional
switching of the ferromagnetic free layer in the MTJ. Compared to electric
current driven STT-MRAM with perpendicular magnetic anisotropy (PMA),
thermoelectric STT-MRAM reduces the overall magnetization switching energy by
more than 40% for nano-second switching, combined with a write error rate (WER)
of less than 10-9 and a lifetime of 10 years or higher. The combination of
higher thermal activation energy, sub-nanosecond read/write speed, improved
tunneling magneto-resistance (TMR) and tunnel barrier reliability make
thermoelectric STT-MRAM a promising choice for future non-volatile memory
applications.",1108.2386v1
2012-03-10,Room temperature ferromagnetism and giant permittivity in chemical routed Co1.5Fe1.5O4 ferrite particles and their composite with NaNO3,"We report structural, magnetic and dielectric properties of Co1.5Fe1.5O4
nanoparticles and their composites with non-magnetic NaNO3. The samples were
derived from metal nitrates solution at different pH values. The chemical
routed sample was air heated at 200 0C and 500 0C. Heating of the material
showed unusual decrease of crystallite size, but cubic spinel structure is seen
in all samples. The samples of Co1.5Fe1.5O4 showed substantially large room
temperature ferromagnetic moment, electrical conductivity, dielectric constant,
and low dielectric loss. The samples are soft ferromagnet and electrically
highly polarized. The interfaces of grains and grain boundaries are actively
participating to determine the magnetic and dielectric properties of the
ferrite grains. The effects of interfacial contribution are better realized
using the ferrite and NaNO3 composite samples. We have examined different
scopes of modifying the magnetic and dielectric parameters using same material
in pure and composite form.",1203.2944v1
2012-10-01,"Effect of Site-disorder, Off-stoichiometry and Epitaxial Strain on the Optical Properties of Magnetoelectric Gallium Ferrite","We present a combined experimental-theoretical study demonstrating the role
of site disorder, off-stoichiometry and strain on the optical behavior of
magnetoelectric gallium ferrite. Optical properties such as band-gap,
refractive indices and dielectric constants were experimentally obtained by
performing ellipsometric studies over the energy range 0.8 eV to 4.2 eV on
pulsed laser deposited epitaxial thin films of stoichiometric gallium ferrite
with b-axis orientation and the data was compared with theoretical results.
Calculations on the ground state structure show that the optical activity in
GaFeO3 arises primarily from O2p-Fe3d transitions. Further, inclusion of site
disorder and epitaxial strain in the ground state structure significantly
improves the agreement between the theory and the room temperature experimental
data substantiating the presence of site-disorder in the experimentally derived
strained GaFeO3 films at room temperature. We attribute the modification of the
ground state optical behavior upon inclusion of site disorder to the
corresponding changes in the electronic band structure, especially in Fe3d
states leading to a lowered band-gap of the material.",1210.0356v1
2015-02-21,On-chip superconducting microwave circulator from synthetic rotation,"We analyze the design of a potential replacement technology for the
commercial ferrite circulators that are ubiquitous in contemporary quantum
superconducting microwave experiments. The lossless, lumped element design is
capable of being integrated on chip with other superconducting microwave
devices, thus circumventing the many performance-limiting aspects of ferrite
circulators. The design is based on the dynamic modulation of DC
superconducting microwave quantum interference devices (SQUIDs) that function
as nearly linear, tunable inductors. The connection to familiar ferrite-based
circulators is a simple frame boost in the internal dynamics' equation of
motion. In addition to the general, schematic analysis, we also give an
overview of many considerations necessary to achieve a practical design with a
tunable center frequency in the 4-8 GHz frequency band, a bandwidth of 240 MHz,
reflections at the -20 dB level, and a maximum signal power of approximately
order 100 microwave photons per inverse bandwidth.",1502.06041v1
2015-04-14,Magnetic charges and magnetoelectricity in hexagonal rare-earth manganites and ferrites,"Magnetoelectric (ME) materials are of fundamental interest and show broad
potential for technological applications. Commonly the dominant contribution to
the ME response is the lattice-mediated one, which is proportional to both the
Born electric charge $Z^{\rm e}$ and its analogue, the dynamical magnetic
charge $Z^{\rm m}$. Our previous study has shown that exchange striction acting
on noncollinear spins induces much larger magnetic charges than those that
depend on spin-orbit coupling. The hexagonal manganites $R$MnO$_3$ and ferrites
$R$FeO$_3$ ($R$ = Sc, Y, In, Ho-Lu) exhibit strong couplings between electric,
magnetic and structural degrees of freedom, with the transition-metal ions in
the basal plane antiferromagnetically coupled through super-exchange so as to
form a 120$^\circ$ noncollinear spin arrangement. Here we present a theoretical
study of the magnetic charges, and of the spin-lattice and spin-electronic ME
constants, in these hexagonal manganites and ferrites, clarifying the
conditions under which exchange striction leads to an enhanced $Z^{\rm m}$
values and anomalously large in-plane spin-lattice ME effects.",1504.03405v1
2015-10-20,First-principles investigation of boron defects in nickel ferrite spinel,"The accumulation of boron within the porous nickel ferrite (NiFe2O4, NFO)
deposited on fuel rods is a major technological problem with important safety
and economical implications. In this work the electronic structure of nickel
ferrite is investigated using first-principles methods, and the results are
combined with experimental data to analyze B incorporation into the NFO
structure. Under thermodynamic equilibrium the calculations predict that the
incorporation of B into the NFO structure is unfavorable. The main limiting
factors are the narrow stability domain of NFO and the precipitation of B2O3,
Fe3BO5, and Ni3B2O6 as secondary phases. In n-type NFO, the most stable defect
is Ni vacancy while in p-type material lowest the formation energy belongs to
tetrahedrally coordinated interstitial B . Because of these limiting conditions
it is more thermodynamically favorable for B to form secondary phases with Fe,
Ni and O than it is to form point defects in NFO",1510.05888v1
2016-07-08,Easy axis orientation of Strontium ferrite thin films described by spin reorientation,"In plane orientation of magnetic easy axis of sputtered strontium hexaferrite
thin films has been explained using classical Heisenberg Hamiltonian. The
variation of average value of in plane spin component with temperature was
plotted in order to determine the temperature at which easy axis is oriented in
the plane of the strontium ferrite film. The average value of in plane spin
component in this 2-D model reaches zero at one particular temperature. This
particular temperature obtained using our theoretical model agrees with the
experimental value of the temperature of rf sputtered polycrystalline strontium
ferrite thin films deposited on polycrystalline Al2O3 substrates (500 0C). This
spin reorientation temperature solely depends on the values of energy
parameters used in our modified Heisenberg Hamiltonian equation.",1607.02327v1
2017-03-31,Spin Seebeck effect in Y-type hexagonal ferrite thin films,"Spin Seebeck effect (SSE) has been investigated in thin films of two
Y-hexagonal ferrites Ba$_2$Zn$_{2}$Fe$_{12}$O$_{22}$ (Zn2Y) and
Ba$_2$Co$_{2}$Fe$_{12}$O$_{22}$ (Co2Y) deposited by a spin-coating method on
SrTiO$_3$(111) substrate. The selected hexagonal ferrites are both
ferrimagnetic with similar magnetic moments at room temperature and both
exhibit easy magnetization plane normal to $c$-axis. Despite that, SSE signal
was only observed for Zn2Y, whereas no significant SSE signal was detected for
Co2Y. We tentatively explain this different behavior by a presence of two
different magnetic ions in Co2Y, whose random distribution over octahedral
sites interferes the long range ordering and enhances the Gilbert damping
constant. The temperature dependence of SSE for Zn2Y was measured and analyzed
with regard to the heat flux and temperature gradient relevant to the SSE
signal.",1703.10903v1
2017-04-08,Effect of annealing temperatures on the electrical conductivity and dielectric properties of Ni1.5Fe1.5O4 spinel ferrite prepared by chemical reaction at different pH values,"The electrical conductivity and dielectric properties of Ni1.5Fe1.5O4 ferrite
has been controlled by varying the annealing temperature of the chemical routed
samples. The frequency activated conductivity obeyed Jonschers power law and
universal scaling suggested semiconductor nature. An unusual metal like state
has been revealed in the measurement temperature scale in between two
semiconductor states with different activation energy. The metal like state has
been affected by thermal annealing of the material. The analysis of electrical
impedance and modulus spectra has confirmed non-Debye dielectric relaxation
with contributions from grains and grain boundaries. The dielectric relaxation
process is thermally activated in terms of measurement temperature and
annealing temperature of the samples. The hole hopping process, due to presence
of Ni3+ ions in the present Ni rich ferrite, played a significant role in
determining the thermal activated conduction mechanism. This work has
successfully applied the technique of a combined variation of annealing
temperature and pH value during chemical reaction for tuning electrical
parameters in a wide range; for example dc limit of conductivity 10power(-4)
-10power(-12) S/cm, and unusually high activation energy 0.17-1.36 eV.",1704.02495v2
2018-05-04,The effect of the misfit dislocation on the in-plane shear response of the ferrite/cementite interface,"Although the pearlitic steel is one of the most extensively studied
materials, there are still questions unanswered about the interface in the
lamellar structure. In particular, to deepen the understanding of the
mechanical behavior of pearlitic steel with fine lamellar structure, it is
essential to reveal the structure-property relationship of the
ferrite/cementite interface (FCI). In this study, we analyzed the in-plane
shear deformation of the FCI using atomistic simulation combined with extended
atomically informed Frank-Bilby (xAIFB) method and disregistry analyses. In the
atomistic simulation, we applied in-plane shear stress along twelve different
directions to the ferrite/cementite bilayer for Isaichev (IS), Near Bagaryatsky
(Near BA) and Near Pitsch-Petch (Near PP) orientation relationship (OR),
respectively. The simulation results reveal that IS and Near BA ORs show
dislocation-mediated plasticity except two directions, while Near PP OR shows
mode II (in-plane shear) fracture at the FCI along all directions. Based on the
xAIFB and disregistry analysis results, we conclude that the in-plane shear
behavior of the FCI is governed by the magnitude of Burgers vector and
core-width of misfit dislocations.",1805.01591v1
2011-11-18,Microwave near-field helicity and its role in the matter-field interaction,"In the preceding paper, we have shown analytically that in a source-free
subwavelength region of microwave fields there exist the field structures with
local coupling between the time-varying electric and magnetic fields differing
from the electric-magnetic coupling in regular free-space electromagnetic
waves. As a source of such near fields, there is a small quasi-2D ferrite disk
with the magnetic-dipolar-mode (MDM) spectra. The near fields originated from a
MDM ferrite particle are characterized by topologically distinctive structures
of power-flow vortices, non-zero helicity, and a torsion degree of freedom. In
this paper, we present numerical and experimental studies on the microwave
near-field helicity and its role in the matter-field interaction. We show that
one can distinguish different microwave near-field-helicity parameters for
different permittivities of dielectric samples loading a ferrite-disk sensor.
We analyze a role of topological structures of the fields on the helicity
properties. We demonstrate dependence of the MDM spectra and the
near-field-helicity parameters from the enantiomeric properties of the loading
samples.",1111.4361v1
2011-11-23,Magnetic and structural characterization of nanosized BaCo_xZn_{2-x}Fe_{16}O_{27} hexaferrite in the vicinity of spin reorientation transition,"Numerous applications of hexagonal ferrites are related to their easy axis or
easy plane magnetocrystalline anisotropy configurations. Certain W-type
ferrites undergo spin reorientation transitions (SRT) between different
anisotropy states on magnetic field or temperature variation. The transition
point can be tuned by modifying the chemical composition, which suggests a
potential application of hexaferrites in room temperature magnetic
refrigeration. Here we present the results of structural and magnetic
characterization of BaCo_xZn_{2-x}Fe_{16}O_{27} (0.7 \leq x \leq 2) doped
barium ferrites. Fine powders were prepared using a sol-gel citrate precursor
method. Crystal structures and particle size distributions were examined by
X-ray diffraction and transmission electron microscopy. The optimal synthesis
temperature ensuring complete formation of single W-phase with limited grain
growth has been determined. Spin reorientation transitions were revealed by
thermomagnetic analysis and AC susceptibility measurements.",1111.5453v1
2011-12-30,Large magnetic circular dichroism in resonant inelastic x-ray scattering at the Mn L-edge of Mn-Zn ferrite,"We report resonant inelastic x-ray scattering (RIXS) excited by circularly
polarized x-rays on Mn-Zn ferrite at the Mn L2,3-resonances. We demonstrate
that crystal field excitations, as expected for localized systems, dominate the
RIXS spectra and thus their dichroic asymmetry cannot be interpreted in terms
of spin-resolved partial density of states, which has been the standard
approach for RIXS dichroism. We observe large dichroic RIXS at the L2-resonance
which we attribute to the absence of metallic core hole screening in the
insulating Mn-ferrite. On the other hand, reduced L3-RIXS dichroism is
interpreted as an effect of longer scattering time that enables spin-lattice
core hole relaxation via magnons and phonons occurring on a femtosecond time
scale.",1201.0091v1
2018-01-24,Quantization of magnetoelectric fields,"The effect of quantum coherence involving macroscopic degree of freedom, and
occurring in systems far larger than individual atoms are one of the topical
fields in modern physics. Because of material dispersion, a phenomenological
approach to macroscopic quantum electrodynamics, where no canonical formulation
is attempted, is used. The problem becomes more complicated when geometrical
forms of a material structure have to be taken into consideration. Magnetic
dipolar mode (MDM) oscillations in a magnetically saturated quasi 2D ferrite
disk are macroscopically quantized states. In this ferrimagnetic structure,
long range dipole dipole correlation in positions of electron spins can be
treated in terms of collective excitations of a system as a whole. The near
fields in the proximity of a MDM ferrite disk have space and time symmetry
breakings. Such MDM-originated fields, called magnetoelectric (ME) fields,carry
both spin and orbital angular momentums. By virtue of unique topology, ME
fields are different from free space electromagnetic (EM) fields. The ME fields
are quantum fluctuations in vacuum. We call these quantized states ME photons.
There are not virtual EM photons. We show that energy, spin and orbital angular
momenta of MDM oscillations constitute the key physical quantities that
characterize the ME field configurations. We show that vacuum can induce a
Casimir torque between a MDM ferrite disk, metal walls, and dielectric samples.",1801.08042v1
2018-10-24,Electronic and optical properties of spinel zinc ferrite: $Ab$ $initio$ hybrid functional calculations,"Spinel ferrites in general show a rich interplay of structural, electronic,
and magnetic properties. Here, we particularly focus on zinc ferrite (ZFO),
which has been observed experimentally to crystallise in the cubic $normal$
spinel structure. However, its magnetic ground state is still under dispute. In
addition, some unusual magnetic properties in ZFO thin films or nanostructures
have been explained by a possible partial cation inversion and a different
magnetic interaction between the two cation sublattices of the spinel structure
compared to the crystalline bulk material. Here, density functional theory has
been applied to investigate the influence of different inversion degrees and
magnetic couplings among the cation sublattices on the structural, electronic,
magnetic, and optical properties. Effects of exchange and correlation have been
modelled using the generalised gradient approximation (GGA) together with the
Hubbard `+$U$' parameter, and the more elaborate hybrid functional PBE0. While
the GGA+$U$ calculations yield an antiferromagnetically coupled $normal$ spinel
structure as the ground state, in the PBE0 calculations the ferromagnetically
coupled $normal$ spinel is energetically slightly favoured, and the hybrid
functional calculations perform much better with respect to structural,
electronic and optical properties.",1810.10555v1
2019-07-30,The effect of heating rate and soaking time on microstructure of an advanced high strength steel,"This work focuses on the effect of soaking time on the microstructure during
ultrafast heat treatment of a 50% cold rolled low carbon steel with initial
ferritic-pearlitic microstructure. Dilatometry analysis was used to estimate
the effect of heating rate on the phase transformation temperatures and to
select an appropriate inter-critical temperature for final heat treatments. A
thorough qualitative and quantitative microstructural characterization of the
heat treated samples is performed using a wide range of characterization
techniques. A complex multiphase, hierarchical microstructure consisting of
ferritic matrix with embedded martensite and retained austenite is formed after
all applied heat treatments. In turn, the ferritic matrix contains
recrystallized and non-recrystallized grains. It is demonstrated that the
ultrafast heating generally results in finer microstructure compared to the
conventional heating independently on the soaking time. There is a significant
effect of the soaking time on the volume fraction of martensite of the
ultrafast heated material, while in the samples heated with conventional
heating rate it remains relatively unchanged during soaking. Recrystallization,
recovery and phase transformations occurring during soaking are discussed with
respect to the applied heating rate.",1907.12767v1
2019-10-24,Zero Field Cooled Exchange Bias Effect in Nano-Crystalline Mg-Ferrite Thin Film,"I report, Zero Field Cooled (ZFC) Exchange Bias (EB) effect in a single phase
nanocrystalline Mg-ferrite thin film, deposited on an amorphous quartz
substrate using pulsed laser ablation technique. The film showed a high ZFC EB
shift (HE~ 190 Oe) at 5 K. The ZFC EB shift decreased with increasing
temperature and disappeared at higher temperatures (T > 70 K). This Mg-ferrite
thin film also showed Conventional Exchange Bias (CEB) effect, but unlike many
CEB systems, the film showed decrease in the coercivity (HC) under the Field
Cooled (FC) measurements. The film also showed training effect in ZFC
measurements which followed the frozen spin relaxation behaviour. The observed
exchange bias could be attributed to the pinning effect of the surface spins of
frozen glassy states at the interface of large ferrimagnetic grains.",1910.10948v1
2012-05-04,First-principles calculation of magnetoelastic coefficients and magnetostriction in the spinel ferrites CoFe2O4 and NiFe2O4,"We present calculations of magnetostriction constants for the spinel ferrites
CoFe2O4 and NiFe2O4 using density functional theory within the GGA+U approach.
Special emphasis is devoted to the influence of different possible cation
distributions on the B site sublattice of the inverse spinel structure on the
calculated elastic and magnetoelastic constants. We show that the resulting
symmetry-lowering has only a negligible effect on the elastic constants of both
systems as well as on the magnetoelastic response of NiFe2O4, whereas the
magnetoelastic response of CoFe2O4 depends more strongly on the specific cation
arrangement. In all cases our calculated magnetostriction constants are in good
agreement with available experimental data. Our work thus paves the way for
more detailed first-principles studies regarding the effect of stoichiometry
and cation inversion on the magnetostrictive properties of spinel ferrites.",1205.0906v1
2019-11-18,Chemical synthesis and magnetic properties of monodisperse cobalt ferrite nanoparticles,"In this work, a successful synthesis of magnetic cobalt ferrite (CoFe2O4)
nanoparticles is presented. The synthesized CoFe2O4 nanoparticles have a
spherical shape and highly monodisperse in the selected solvent. The effect of
different reaction conditions such as temperature, reaction time and varying
capping agents on the phase and morphology is studied. Scanning transmission
electron microscopy showed that the size of these nanoparticles can be
controlled by varying reaction conditions. Both X-ray diffraction and energy
dispersive X-ray spectroscopy corroborate the formation of CoFe2O4 spinel
structure with cubic symmetry. Due to optimized reaction parameters, each
nanoparticle was shown to be a single magnetic domain with diameter ranges from
6 to 16 nm. Finally, the magnetic investigations showed that the obtained
nanoparticles are superparamagnetic with a small coercivity value of about 315
Oe and a saturation magnetization of 58 emu/g at room temperature. These
results make the cobalt ferrite nanoparticles promising for advanced magnetic
nanodevices and biomagnetic applications.",1911.07496v1
2020-09-08,On the assessment of an optimized method to determine the number of turns and the air gap length in ferrite-core low-frequency-current biased inductors,"This paper presents a first assessment of a design method aiming at the
minimization of the number of turns $N$ and the air gap length $g$ in
ferrite-core based low-frequency-current biased AC filter inductors. Several
design cases are carried on a specific model of Power Module (PM) core, made of
distinct ferrite materials and having different kinds of air gap arrangements
The correspondingly obtained design results are firstly compared with the
classic approach by linearization of the magnetic curve to calculate $N$ and
the use of a fringing factor to determine $g$. Next, a refined design approach
of specifying the inductance roll-off at the peak current and its potential
limitations are discussed with respect to our design method. Finally, the
behaviour of inductors operated beyond their design specifications is analyzed.",2009.03750v1
2020-11-06,Phase boundary near a magnetic percolation transition,"Motivated by recent experimental observations [Phys. Rev. 96, 020407 (2017)]
on hexagonal ferrites, we revisit the phase diagrams of diluted magnets close
to the lattice percolation threshold. We perform large-scale Monte Carlo
simulations of XY and Heisenberg models on both simple cubic lattices and
lattices representing the crystal structure of the hexagonal ferrites. Close to
the percolation threshold $p_c$, we find that the magnetic ordering temperature
$T_c$ depends on the dilution $p$ via the power law $T_c \sim |p-p_c|^\phi$
with exponent $\phi=1.09$, in agreement with classical percolation theory.
However, this asymptotic critical region is very narrow, $|p-p_c| \lesssim
0.04$. Outside of it, the shape of the phase boundary is well described, over a
wide range of dilutions, by a nonuniversal power law with an exponent somewhat
below unity. Nonetheless, the percolation scenario does not reproduce the
experimentally observed relation $T_c \sim (x_c -x)^{2/3}$ in
PbFe$_{12-x}$Ga$_x$O$_{19}$. We discuss the generality of our findings as well
as implications for the physics of diluted hexagonal ferrites.",2011.03390v3
2021-05-28,Anisotropic Magnon Spin Transport in Ultra-thin Spinel Ferrite Thin Films -- Evidence for Anisotropy in Exchange Stiffness,"We report measurements of magnon spin transport in a spinel ferrite,
magnesium aluminum ferrite $\mathrm{MgAl_{0.5}Fe_{1.5}O_4}$ (MAFO), which has a
substantial in-plane four-fold magnetic anisotropy. We observe spin diffusion
lengths $> 0.8$ $\mathrm{\mu m}$ at room temperature in 6 nm films, with spin
diffusion length 30% longer along the easy axes compared to the hard axes. The
sign of this difference is opposite to the effects just of anisotropy in the
magnetic energy for a uniform magnetic state. We suggest instead that
accounting for anisotropy in exchange stiffness is necessary to explain these
results.",2105.13943v1
2021-08-09,Designing order-disorder transformation in high-entropy ferritic steels,"Order-disorder transformations hold an essential place in chemically complex
high-entropy ferritic-steels (HEFSs) due to their critical technological
application. The chemical inhomogeneity arising from mixing of multi-principal
elements of varying chemistry can drive property altering changes at the atomic
scale, in particular short-range order. Using density-functional theory based
linear-response theory, we predict the effect of compositional tuning on the
order-disorder transformation in ferritic steels -focusing on Cr-Ni-Al-Ti-Fe
HEFSs. We show that Ti content in Cr-Ni-Al-Ti-Fe solid solutions can be tuned
to modify short-range order that changes the order-disorder path from BCC-B2
(Ti atomic-fraction = 0) to BCC-B2-L21 (Ti atomic-faction $>$ 0) consistent
with existing experiments. Our study suggests that tuning degree of SRO through
compositional variation can be used as an effective means to optimize phase
selection in technologically useful alloys.",2108.04110v1
2021-12-02,Strain Engineering of Magnetic Anisotropy in Epitaxial Films of Cobalt Ferrite,"Perpendicular magnetic anisotropy (PMA) energy up to
$K_{\mathrm{u}}=6.1\pm0.8$ MJ m$^{-3}$ is demonstrated in this study by
inducing large lattice-distortion exceeding 3% at room temperature in
epitaxially distorted cobalt ferrite Co$ _{x} $Fe$ _{3-x} $O$ _{4} $ (x = 0.72)
(001) thin films. Although the thin film materials include no rare-earth
elements or noble metals, the observed $ K_{u} $ is larger than that of the
neodymium-iron-boron compounds for high-performance permanent magnets. The
large PMA is attributed to the significantly enhanced magneto-elastic effects,
which are pronounced in distorted films with epitaxial lattice structures upon
introducing a distortion control layer of composition Mg$ _{2-x} $Sn$_{1+x}$O$
_{4} $. Surprisingly, the induced $ K_{u} $ can be quantitatively explained in
terms of the agreement between the local crystal field of Co$ ^{2+} $ and the
phenomenological magneto-elastic model, indicating that the linear response of
induced $K_u$ is sufficiently valid even under lattice distortions as large as
3.2%. Controlling tetragonal lattice deformation using a non-magnetic spinel
layer for ferrites could be a promising protocol for developing materials with
large magnetic anisotropies.",2112.00916v1
2022-03-30,Origin of Perpendicular Magnetic Anisotropy in Co$_x$Fe$_{3-x}$O$_{4+δ}$ Thin Films Studied by X-ray Magnetic Circular and Linear Dichroisms,"We investigate the element-specific spin and orbital states and their roles
on magnetic anisotropy in the Co-ferrite (Co$_x$Fe$_{3-x}$O$_{4+\delta}$ (001))
thin films which exhibit perpendicular magnetic anisotropy (PMA). The origin of
PMA in the low $x$ region ($x$ $<$ 1) can be mainly explained by the large
perpendicular orbital magnetic moments in the Co$^{2+}$ (3$d^7$) states
detected by X-ray magnetic circular and linear dichroisms (XMCD/XMLD). The XMLD
for a PMA film ($x=0.2$) with square hysteresis curve shows the oblate charge
distribution in the Co$^{2+}$ site, which is consistent with the change in
local nearest neighbor distance in Co detected by extended X-ray absorption
fine structure analysis. Our finding reveals that the microscopic origin of PMA
in Co-ferrite comes from the enhanced orbital magnetic moments along
out-of-plane [001] direction through in-plane charge distribution by tensile
strain, which adds the material functionalities in spinel ferrite thin films
from the viewpoint of strain and orbital magnetic moments.",2203.16061v1
2023-02-13,Improper ferroelectricity in ultrathin hexagonal ferrites film,"The suppression of ferroelectricity in ultrathin films of improper
ferroelectric hexagonal ferrites or manganites has been attributed to the
effect of interfacial clamping, however, the quantitative understanding and
related phenomenological model are still lacking. In this work, we report the
paraelectric-to-ferroelectric phase transition of epitaxial h-ScFeO3 films with
different thickness through in-situ reflection high-energy electron diffraction
(RHEED). Based on the interfacial clamping model and the Landau theory, we show
that the thickness-dependence of the ferroelectric Curie temperature can be
understood in terms of the characteristic length of interfacial clamping layer
and the bulk Curie temperature. Furthermore, we found that the critical
thickness of improper ferroelectricity is proportional to the characteristic
length of interfacial clamping layer. These results reveal the essential role
of mechanical clamping from interface on the improper ferroelectricity of
hexagonal ferrites or manganites, and could serve as the guidance to achieve
robust improper ferroelectricity in ultrathin films.",2302.06532v1
2023-03-14,Electromagnetic Waves Propagation along Tangentially Magnetised Bihyrotropic Layer (with Example of Spin Waves in Ferrite Plate),"Analytically, without magnetostatic approximation, the problem of
electromagnetic wave propagation along arbitrary direction in a tangentially
magnetized bihyrotropic layer has been solved. It is found that one can bring
the Maxwell equations for this problem to the fourth order differential
equation and the obtained biquadratic characteristic equation determines two
different wave numbers kx21 and kx22 describing the wave distribution over the
layer thickness. The dispersion equation describing wave propagation in the
bihyrotropic layer was obtained for the case of real kx21 and kx22 values. It
is shown that in a ferrite plate, which is a special case of a bihyrotropic
layer, three types of wave distribution over the plate thickness can take
place: surface-surface (when kx21 and kx22 are real numbers), volume-surface
(kx21 is imaginary and kx22 is real) and volume-volume distribution (kx21 and
kx22 are imaginary numbers). Characteristics of the surface spin wave in
ferrite plate are investigated. It is found that dependences of the wave
numbers kx21 and kx22 on the wave vector orientation are significantly
different from the similar magnetostatic dependence for a large part of the
wave spectrum.",2303.08800v1
2023-09-27,On the potential of hard ferrite ceramics for permanent magnet technology -- a review on sintering strategies,"A plethora of modern technologies rely on permanent magnets for their
operation, including many related to the transition towards a sustainable
future, such as wind turbines or electric vehicles. Despite the overwhelming
superiority of magnets based on rare-earth elements in terms of the magnetic
performance, the harmful environmental impact of the mining of these raw
materials, their uneven distribution on Earth and various political conflicts
among countries leave no option but seeking for rare-earth-free alternatives.
The family of the hexagonal ferrites or hexaferrites, and in particular the
barium and strontium M-type ferrites (BaFe12O19 and SrFe12O19), are strong
candidates for a partial rare-earth magnets substitution, and they are indeed
successfully implemented in multiple applications. The manufacturing of
hexaferrites into dense pieces (i.e. magnets) meeting the requirements of the
specific application (e.g. magnetic and mechanical properties, shape) is not
always straightforward, which has in many cases hampered the actual
substitution at the industrial level. Here, past and on-going research on
hexaferrites sintering is reviewed with a historical perspective, focusing on
the challenges encountered and the solutions explored, and correlating the
sintering approaches with the magnetic performance of the resulting ceramic
magnet.",2309.15680v1
2024-01-20,Charge transfer transitions and circular magnetooptics in ferrites,"The concept of charge-transfer (CT) transitions in ferrites is based on the
cluster approach and takes into account the relevant interactions as the
low-symmetry crystal field, spin-orbital, Zeeman, exchange and
exchange-relativistic interactions. For all its simplicity, this concept yield
a reliable qualitative and quantitative microscopic explanation of spectral,
concentration, temperature, and field dependences of optic and magneto-optic
properties ranging from the isotropic absorption as well as the optic
anisotropy to the circular magneto-optics. In this review paper, starting with
a critical analysis of the fundamental shortcomings of the ""first-principles""
DFT-based band theory we present the main ideas and techniques of the cluster
theory of the CT transitions to be main contributors to circular magneto-optics
of ferrites.",2401.11267v1
2013-03-01,Dispersive Casimir Pressure Effect from Surface Plasmon Quanta by Quasi 1D Metal Wires in Ferrite Disks and The Josephson Frequencies and Currents,"Ferrites are distinct material for electromagnetic applications due to its
unique spin precession. In this paper, Casimir pressure effect by deploying
magnetically tunable surface plasmon quanta in stratified structure of using
ferrite and metal wires is presented. Previously, oscillating surface plasmon
quanta were successfully included to modify first reflection and first
transmission characteristics. The oscillating surface plasmon quanta in the
modified reflection in such a system, not only does resolve in a typical matter
in metamaterial, but also provide new applications such as creating Casimir
pressure effects through the metamaterial composite shown in this paper. The
Casimir pressure flips from attractive state to repulsive state is referred to
cause mechanism of radiation from surface plasmon quanta. Both Casimir force
analysis and the measured data of radiations indicate us the system develops
quantized states by electric flux induced by ferromagnetic resonance. Quantum
analysis is used to understand the discrete radiations spectra for our
experimental measurement. The discrete radiations are reproduced by using time
dependent Schr\""odinger representation. As a result, we find the Josephson
frequency and Josephson current representations at room temperature and we used
them for extrapolating voltage induced in excited ferrites. Josephson frequency
at X-band is able to differentiate micron volt differences and it allows us to
report the data for voltage induced by ferromagnetic resonance in ferrite at
room temperature. It is understood that the radiation intensity depends on
density of final states and excitation probability when we come to think the
energy matter. It seems possible to create as high as 20mW microwave power
inside waveguide at X-band.",1303.0205v2
2023-09-24,Quantifying Li-content for compositional tailoring of lithium ferrite ceramics,"Owing to their multiple applications, lithium ferrites are relevant materials
for several emerging technologies. For instance, LiFeO2 has been spotted as an
alternative cathode material in Li-ion batteries, while LiFe5O8 is the lowest
damping ferrite, holding promise in the field of spintronics. The Li-content in
lithium ferrites has been shown to greatly affect the physical properties, and
in turn, the performance of functional devices based on these materials.
Despite this, lithium content is rarely accurately quantified, as a result of
the low number of electrons in Li hindering its identification by means of
routine materials characterization methods. In the present work, magnetic
lithium ferrite powders with Li:Fe ratios of 1:1, 1:3 and 1:5 have been
synthesized, successfully obtaining phase-pure materials (LiFeO2 and LiFe5O8),
as well as a controlled mixture of both phases. The powders have been compacted
and subsequently sintered by thermal treatment (Tmax = 1100 {\deg}C) to
fabricate dense pellets which preserve the original Li:Fe ratios. Li-content on
both powders and pellets has been determined by two independent methods: (i)
Rutherford backscattering spectroscopy combined with nuclear reaction analysis
and (ii) Rietveld analysis of powder X-ray diffraction data. With good
agreement between both techniques, it has been confirmed that the Li:Fe ratios
employed in the synthesis are maintained in the sintered ceramics. The same
conclusion is drawn from spatially-resolved confocal Raman microscopy
experiments on regions of a few microns. Field emission scanning electron
microscopy has evidenced the substantial grain growth taking place during the
sintering process - mean particle sizes rise from about 600 nm in the powders
up to 3.8(6) um for dense LiFeO2 and 10(2) um for LiFe5O8 ceramics.",2309.14377v1
2007-01-14,Nano Ferrites Microwave Complex Permeability and Permittivity Measurements by T/R Technique in Waveguide,"There is a huge demand to accurately determine the magneto-electrical
properties of particles in the nano sized regime due to the modern IC
technology revolution and biomedical application science. In this paper, we
present a microwave waveguide measurement technique for complex permeability
and permittivity of expensive nano sized magnetic powder materials. In the
measurement process, Agilents 8510C vector network analyzer was used to have a
standard TRL calibration for free space inside the waveguides. In order to
maintain the recommended insertion phase range, a very thin prepared sample was
loaded inside the calibrated waveguide. Also, the loaded materials magnetic and
dielectric effects were considered into the cutoff wavelength of the
propagation constant of the TE10 wave from the geometrical dimensions of the
waveguides. This makes the measured permeability and permittivity more reliable
than commonly used techniques. The six different compounds of nano sized
ferrite powders (Fe3O4, CuFe2O4, CuFe2O4Zn, Fe2NiO3Zn, BaFe12O19, and
SrFe12O19), in which the average diameter of nano particles is less than 40nm
were purchased from Sigma-Aldrich, Inc for measurement purposes employing this
technique. For industrial benefits, we present the complex permeability and
permittivity on the frequency range from 3.95GHz to 5.85GHz. The measured
results showed that the dielectric permittivity of these materials is quite
different from those of solid state materials. Index Terms, Nano ferrites,
waveguide technique, permeability, permittivity.",0701307v2
2016-02-18,From Fe$_3$O$_4$/NiO bilayers to NiFe$_2$O$_4$-like thin films through Ni interdiffusion,"Ferrites with (inverse) spinel structure display a large variety of
electronic and magnetic properties making some of them interesting for
potential applications in spintronics. We investigate the thermally induced
interdiffusion of Ni$^{2+}$ ions out of NiO into Fe$_3$O$_4$ ultrathin films
resulting in off-stoichiometric nickelferrite-like thin layers. We synthesized
epitaxial Fe$_3$O$_4$/NiO bilayers on Nb-doped SrTiO$_3$(001) substrates by
means of reactive molecular beam epitaxy. Subsequently, we performed an
annealing cycle comprising three steps at temperatures of 400\,$^{\circ}$C,
600\,$^{\circ}$C, and 800\,$^{\circ}$C under an oxygen background atmosphere.
We studied the changes of the chemical and electronic properties as result of
each annealing step with help of hard x-ray photoelectron spectroscopy and
found a rather homogenous distribution of Ni and Fe cations throughout the
entire film after the overall annealing cycle. For one sample we observed a
cationic distribution close to that of the spinel ferrite NiFe$_2$O$_4$.
Further evidence comes from low energy electron diffraction patterns indicating
a spinel type structure at the surface after annealing. Site and element
specific hysteresis loops performed by x-ray magnetic circular dichroism
uncovered the antiferrimagnetic alignment between the octahedral coordinated
Ni$^{2+}$ and Fe$^{3+}$ ions and the Fe$^{3+}$ in tetrahedral coordination. We
find a quite low coercive field of 0.02\,T, indicating a rather low defect
concentration within the thin ferrite films.",1602.05773v1
2017-03-19,"Magnetic properties of Sn-substituted Ni-Zn ferrite:synthesized from nano-sized powders of NiO, ZnO, Fe2O3 and SnO2","A series of Ni0.6-x/2Zn0.4-x/2SnxFe2O4 (x = 0.0, 0.05, 0.1, 0.15, 0.2 and
0.3) (NZSFO) ferrite composites have been synthesized from nano powders using
standard solid state reaction technique. The spinel cubic structure of the
investigated samples has been observed by the X-ray diffraction (XRD). The
magnetic properties such as saturation magnetization (Ms), remanent
magnetization (Mr), coercive field (Hc) and Bohr magneton (B) are calculated
from the hysteresis loops. The value of Ms is found to decrease with increasing
Sn content in the samples. This change has been successfully explained by the
variation of A-B interaction strength due to Sn substitution in different
sites. The compositional stability and quality of the prepared ferrite
composites have also been endorsed by the fairly constant initial permeability
(/) over a wide range of frequency region. The decreasing trend of / with
increasing Sn content has been observed. Curie temperature (TC) has found to
increase with the increase in Sn content. Wide spread frequency utility zone
indicates that the NZSFO can be considered as a good candidate for use in
broadband pulse transformer and wide band read-write heads for video recording.
The abnormal behavior for x = 0.05 has been explained with existing theory.",1703.06385v1
2013-08-28,Innate character and theory model about channel segregation in a sand mold steel ingot,"The channel segregation is a severe casting defect in steel ingots. The
formation of channel segregation is generally attributed to the solute
partition and the interdendritic thermosolutal convection in the mushy zone. In
this article, the channel segregation in a steel ingot was carefully
characterized by detailed experimental observation. A different formation
mechanism for the channel segregation was revealed. In the mushy zone of the
ingot, large amount of separate MnS inclusions move laterally and upwards. Some
MnS inclusions will remain in the moving trace of inclusions. Such residual MnS
inclusions appear as large amount of separate MnS inclusion chains. In the
subsequent solid phase transition process, promoted by the MnS chains, ferrite
prefers to forms form the austenite near the MnS inclusions and shows as large
amount of separate ferrite chains. Large amount of ferrite chains align in a
strip-like zone, which results in so called channel segregation in
macro-etching. The physical model about the driving force for the MnS movement
is further theoretically analyzed. In the mushy zone, the interface tension
resultant applied on the MnS inclusions can act as the drive force for the
lateral movement of MnS inclusions. And the buoyance applied on the MnS
inclusions act as the drive force for the upwards movement.",1308.6032v2
2016-07-17,Second order perturbed Heisenberg Hamiltonian of Fe3O4 ultra-thin films,"Due to the wide range of applications, theoretical models of Fe3O4 films are
found to be important. Ultra thin Fe3O4 films with ferrite structure have been
theoretically investigated using second order perturbed modified Heisenberg
Hamiltonian. Matrices for ultra thin films with two and three spin layers are
presented in this manuscript. Total magnetic energy was expressed in terms of
spin exchange interaction, magnetic dipole interaction, second order magnetic
anisotropy and stress induced magnetic anisotropy. Magnetic properties were
observed for films with two spin layers and variant second order magnetic
anisotropy. For the film with three spin layers, second order anisotropy
constant was fixed to avoid tedious derivations. Magnetic easy axis rotates
toward the in plane direction as the number of spin layers is increased from
two to three because the stress induced anisotropy energy dominates at higher
number of spin layers. According to some other experimental data, the magnetic
easy axis of thin films rotates toward the in plane direction as the thickness
is increased. For ferrite film with two spin layers, magnetic easy and hard
directions can be observed at 0.75 and 1.2 radians, respectively, when the
ratio of stress induced anisotropy to the long range dipole interaction
strength is 3.9. For ferrite film with three spin layers, magnetic easy and
hard directions can be observed at 2.4 and 2.3 radians, respectively, when the
ratio of stress induced anisotropy to the long range dipole interaction
strength is 4.2.",1611.02225v2
2017-09-28,Magnetization and Anisotropy of Cobalt Ferrite Thin Films,"The magnetization of thin films of cobalt ferrite frequently falls far below
the bulk value of 455 kAm-1, which corresponds to an inverse cation
distribution in the spinel structure with a significant orbital moment of about
0.6 muB that is associated with the octahedrally-coordinated Co2+ ions. The
orbital moment is responsible for the magnetostriction and magnetocrystalline
anisotropy, and its sensitivity to imposed strain. We have systematically
investigated the structure and magnetism of films produced by pulsed-laser
deposition on different substrates (TiO2, MgO, MgAl2O4, SrTiO3, LSAT, LaAlO3)
and as a function of temperature (500-700 C) and oxygen pressure (10-4 - 10
Pa). Magnetization at room-temperature ranges from 60 to 440 kAm-1, and
uniaxial substrate-induced anisotropy ranges from +220 kJm-3 for films on
deposited on MgO (100) to -2100 kJm-3 for films deposited on MgAl2O4 (100),
where the room-temperature anisotropy field reaches 14 T. No rearrangement of
high-spin Fe3+ and Co2+ cations on tetrahedral and octahedral sites can reduce
the magnetization below the bulk value, but a switch from Fe3+ and Co2+ to Fe2+
and low-spin Co3+ on octahedral sites will reduce the low-temperature
magnetization to 120 kAm-1, and a consequent reduction of Curie temperature can
bring the room-temperature value to near zero. Possible reasons for the
appearance of low-spin cobalt in the thin films are discussed.
  Keywords; Cobalt ferrite, thin films, pulsed-laser deposition, low-spin Co3+,
strain engineering of magnetization.",1709.09965v1
2017-11-14,Cluster dynamics modeling of Mn-Ni-Si precipitates in ferritic-martensitic steel under irradiation,"Mn-Ni-Si precipitates (MNSPs) are known to be responsible for
irradiation-induced hardening and embrittlement in structural alloys used in
nuclear reactors. Studies have shown that precipitation of the MNSPs in 9-Cr
ferritic-martensitic (F-M) alloys, such as T91, is strongly associated with
heterogeneous nucleation on dislocations, coupled with radiation-induced solute
segregation to these sinks. Therefore it is important to develop advanced
predictive models for Mn-Ni-Si precipitation in F-M alloys under irradiation
based on an understanding of the underlying mechanisms. Here we use a cluster
dynamics model, which includes multiple effects of dislocations, to study the
evolution of MNSPs in a commercial F-M alloy T91. The model predictions are
calibrated by data from proton irradiation experiments at 400 {\deg}C.
Radiation induced solute segregation at dislocations is evaluated by a
continuum model that is integrated into the cluster dynamics simulations,
including the effects of dislocations as heterogeneous nucleation sites. The
result shows that MNSPs in T91 are primarily irradiation-induced and, in
particular, both heterogeneous nucleation and radiation-induced segregation at
dislocations are necessary to rationalize the experimental observations.",1711.05008v1
2018-06-29,High quality cobalt ferrite ultrathin films with large inversion parameter grown in epitaxy on Ag(001),"Cobalt ferrite ultrathin films with inverse spinel structure are among the
best candidates for spin-filtering at room temperature. We have fabricated
high-quality epitaxial ultrathin CoFe2O4 layers on Ag(001) following a
three-step method: an ultrathin metallic CoFe2 alloy was first grown in
coherent epitaxy on the substrate, and then treated twice with O2, first at RT
and then during annealing. The epitaxial orientation, the surface, interface
and film structure were resolved combining LEED, STM, Auger and in situ GIXRD.
A slight tetragonal distortion was observed, that should drive the easy
magnetization axis in plane due to the large magneto-elastic coupling of such a
material. The so-called inversion parameter, i.e. the Co fraction occupying
octahedral sites in the ferrite spinel structure, is a key element for its
spin-dependent electronic gap. It was obtained through in-situ x-ray resonant
diffraction measurements collected at both the Co and Fe K edges. The data
analysis was performed using the FDMNES code and showed that Co ions are
predominantly located at octahedral sites with an inversion parameter of 0.88
+- 0.05. Ex-situ XPS gave an estimation in accordance with the values obtained
through diffraction analysis.",1807.00060v1
2019-03-04,Structural and magnetic properties in sputtered iron oxide epitaxial thin films -- Magnetite Fe$_3$O$_4$ and epsilon ferrite e-Fe$_2$O$_3$,"Epitaxial thin film fabrication of iron oxides including magnetite Fe3O4 and
epsilon-ferrite epsilon-Fe2O3 with the potential for advancing electromagnetic
devices has been investigated, which led to the first ever epsilon-ferrite
epitaxial layer being synthesized in the conventional sputtering process.
Concerning Fe3O4 (100) / MgO (100) films, a cube-on-cube epitaxial relationship
and sharp rocking curves with FWHM of 50 - 350 arcsec were confirmed regardless
of the small amount of Ge additions. Sputtering Ar gas pressure PAr heavily
influenced their magnetic and transport properties. High PAr = 15 mTorr caused
a high magnetization of 6.52 kG for the Ge added sample and the clear Verwey
transition at 122 K for the non Ge addition case. Conversion electron Mossbauer
spectroscopy (CEMS) measurements revealed that low PAr < 10 mTorr causes Fe/O
off-stoichiometry on the oxidizing side for the non Ge addition case and the
reductive side for the Ge addition case, respectively. Regarding the
epsilon-Fe2O3 (001) / SrTiO3(111) epilayer synthesis, bilayer microstructure
composed of an approximately 5nm thick initially grown epsilon-Fe2O3 (001)
epilayer and subsequently grown e-Fe2O3 (001) epilayer was confirmed from
cross-sectional TEM observations. The coexistence of magnetically hard and soft
phases was confirmed from the magnetization measurements. As a possible
application of the single nm thick epsilon-Fe2O3 layer, 4-resistive-state
multiferroic tunnel junction (MFTJ) is considered.",1903.01022v1
2020-09-10,Charge-Spin Interconversion in Epitaxial Pt Probed by Spin-Orbit Torques in a Magnetic Insulator,"We measure spin-orbit torques (SOTs) in a unique model system of
all-epitaxial ferrite/Pt bilayers to gain insights into charge-spin
interconversion in Pt. With negligible electronic conduction in the insulating
ferrite, the crystalline Pt film acts as the sole source of charge-to-spin
conversion. A small field-like SOT independent of Pt thickness suggests a weak
Rashba-Edelstein effect at the ferrite/Pt interface. By contrast, we observe a
sizable damping-like SOT that depends on the Pt thickness, from which we deduce
the dominance of an extrinsic spin-Hall effect (skew scattering) and
Dyakonov-Perel spin relaxation in the crystalline Pt film. Furthermore, our
results point to a large internal spin-Hall ratio of $\approx$0.8 in epitaxial
Pt. Our experimental work takes an essential step towards understanding the
mechanisms of charge-spin interconversion and SOTs in Pt-based
heterostructures, which are crucial for power-efficient spintronic devices.",2009.04894v3
2020-10-22,"Structural and Magnetic Characterization of CuxMn1-xFe2O4 (x= 0.0, 0.25) Ferrites Using Neutron Diffraction and Other Techniques","Manganese ferrite (MnFe2O4) and copper doped manganese ferrite
(Mn0.75Cu0.25Fe2O4) soft materials were synthesized through solid-state
sintering method. The phase purity and quality were confirmed from x-ray
diffraction patterns. Then the samples were subjected to neutron diffraction
experiment and the diffraction data were analyzed using FullProf software
package. The surface morphology of the soft material samples was studied using
a scanning electron microscope (SEM). Crystal parameters, crystallite
parameters, occupancy at A and B sites of the spinel structure, magnetic
moments of the atoms at various locations, symmetries, oxygen position
parameters, bond lengths etc. were measured and compared with the reference
data. In MnFe2O4, both octahedral (A) and tetrahedral (B) positions are shared
by Mn2+ and Fe2+/3+ cations, here A site is predominantly occupied by Fe2+ and
B site is occupied by Mn at 0.825 occupancy. The Cu2+ ions in Cu0.25Mn0.75Fe2O4
mostly occupy the B site. Copper mostly occupy the Octahedral (16d) sites. The
length of the cubic lattice decreases with the increasing Copper content. The
magnetic properties, i.e. A or B site magnetic moments, net magnetic moment
etc. were measured using neutron diffraction analysis and compared with the
bulk magnetic properties measured with VSM studies.",2010.11739v1
2021-10-18,Control of Electrochemical Corrosion Properties by Influencing Mn Partitioning through Intercritically Annealing of Medium-Mn Steel,"Medium-Mn steels exhibit excellent mechanical properties and lower production
costs compared to high-Mn steels, which makes them a potential material for
future application in the automotive industry. Intercritical annealing (ICA)
after cold rolling allows to control the stacking fault energy (SFE) of
austenite, the fraction of ferrite and reverted austenite, and the element
partitioning (especially Mn). Although Mn deteriorates the corrosion behavior
of Fe-Mn-Al alloys, the influence of austenite fraction and element
partitioning of Mn on the electrochemical corrosion behavior has not been
investigated yet. Therefore, the electrochemical corrosion behavior in 0.1 M
H2SO4 of X6MnAl12-3, which was intercritically annealed for 2 h at 550 {\deg}C,
600 {\deg}C and 700 {\deg}C, was investigated by potentiodynamic polarization
(PDP), electrochemical impedance spectroscopy (EIS) and mass spectroscopy with
inductively coupled plasma (ICP-MS). Additionally, specimens after 1 h and 24 h
of immersion were examined via SEM to visualize the corrosion damage. The ICA
specimens showed a selective dissolution of reverted austenite due to its
micro-galvanic coupling with the adjacent ferrite. The severity of the
micro-galvanic coupling can be reduced by decreasing the interface area as well
as the chemical gradient of mainly Mn between ferrite and reverted austenite by
ICA.",2110.09205v1
2022-06-30,Modified Z-Phase Formation in a 12% Cr Tempered Martensite Ferritic Steel during Long-Term Creep,"The formation of modified Z-phase in a 12Cr1MoV (German grade: X20) tempered
martensite ferritic (TMF) steel subjected to interrupted long-term
creep-testing at 550$^{\circ}$C and 120 MPa was investigated. Quantitative
volumetric measurements collected from thin-foil and extraction replica samples
showed that modified Z-phase precipitated in both the uniformly-elongated gauge
($f_v$: 0.23 $\pm$ 0.02 %) and thread regions ($f_v$: 0.06 $\pm$ 0.01 %) of the
sample that ruptured after 139 kh. The formation of modified Z-phase was
accompanied by a progressive dissolution of MX precipitates, which decreased
from ($f_v$: 0.16 $\pm$ 0.02 %) for the initial state to ($f_v$: 0.03 $\pm$
0.01 %) in the uniformly-elongated gauge section of the sample tested to
failure. The interparticle spacing of the creep-strengthening MX particles
increased from ($\lambda_{3D}$: 0.55 $\pm$ 0.05 $\mu m$) in the initial state
to ($\lambda_{3D}$: 1.01 $\pm$ 0.10 $\mu m$) for the uniformly-elongated gauge
section of the ruptured sample, while the thread region had an interparticle
spacing of ($\lambda_{3D}$: 0.60 $\pm$ 0.05 $\mu m$). The locally deformed
fracture region had an increased phase fraction of modified Z-phase ($f_v$:
0.40 $\pm$ 0.20 %), which implies that localised creep-strain strongly promotes
the formation of modified Z-phase. The modified Z-phase precipitates did not
form only on prior-austenite grain boundaries and formed throughout the
tempered martensite ferritic grain structure.",2206.15070v1
2022-08-24,Complex magnetoelectric effect in PFN-PT/CoFe$_{2-x}$Zn$_x$O$_4$ bulk particulate composites,"The structural, dielectric, magnetic, and magnetoelectric (ME) properties of
particulate composites containing lead-iron niobate and lead titanate
piezoelectric 0.94[PbFe$_{0.5}$Nb$_{0.5}$O$_3$]-0.06[PbTi$_{0.5}$O$_3$]
(PFN-PT) and Zn-substituted cobalt ferrite magnetostrictive
CoFe$_{2-x}$Zn$_{x}$O$_4$ (CF$_{2-x}$Z$_{x}$O);
0.6(PFN-PT)/0.4(CF$_{2-x}$Z$_{x}$O), x=0, 0.025, 0.1, 0.2, 0.3 (with ratio of
60 Wt\% ferroelectric and 40 Wt\% ferrite); have been investigated. We
investigated the ME voltage coefficient as a complex quantity for all composite
samples using the dynamic piezomagnetic coefficient, $q^{ac}$=$\partial
\lambda^{ac}/{\partial H}$. The results reveal that tuning the magnetostrictive
phase has a strong effect on the real part of the ME voltage coefficient.
Doping zinc into cobalt ferrite modified the magnetic properties of the
magnetic phase, such as magnetic anisotropy and coercive field, and hence the
ME properties. The highest ME coefficient value of 12.33 $\frac{mV}{cm. Oe}$
was obtained for x=0.1 at the magnetic field of 755 Oe. In addition, the
magnetic field at which the maximum value of the ME coefficient was observed
($H_{peak}$) strongly depends on the value of Zn substitution. The results were
interpreted using the magnetic field dependence of the CF$_{2-x}$Z$_{x}$O
magnetostriction.",2208.11317v1
2023-05-07,Band gap and pseudocapacitance of Gd$_2$O$_3$ doped with Ni$_{0.5}$Zn$_{0.5}$Fe$_2$O$_4$,"Herein, we present a detailed study of the structural, optical, and
electrochemical responses of Gd$_2$O$_3$ doped with nickel zinc ferrite
nanoparticles. Doping of Ni$_{0.5}$Zn$_{0.5}$Fe$_2$O$_4$ nanoparticles to
Gd$_2$O$_3$ powder was done through thermal decomposition at 1000 C. The
average grain size of the mixture was determined to be approximately 95 nm, and
phases of cubic Gd$_2$O$_3$, GdO, and orthorhombic prisms of GdFeO$_3$ were
identified. The focused ion beam energy dispersive X-ray spectrum (FIB-EDX)
mapping results clearly show the morphology of the particles with Gd and Fe as
the dominant elements. The structural data were compared with the spectroscopic
measurements confirming the formation of multiple phases of oxides and
ferrites. The measured optical band gap is significantly redshifted to 1.8 eV
and is close to that of nitride compounds of gadolinium metal. The measured
specific capacitance was almost 7 Fg-1 at a current density of 1 Ag-1, showing
a small drop of 27% when the current density is increased to 10 Ag-1. Cyclic
voltammetry (CV) plots of the ferrite doped Gd2O3 electrode at a scan rate of 5
to 100 mV/s indicate the pseudocapacitive nature of the material.",2305.04370v1
2023-06-06,Stress evolution in plastically deformed austenitic and ferritic steels determined using angle- and energy-dispersive diffraction,"In the presented research, the intergranular elastic interaction and the
second-order plastic incompatibility stress in textured ferritic and austenitic
steels were investigated by means of diffraction. The lattice strains were
measured inside the samples by the multiple reflection method using high energy
X-rays diffraction during uniaxial in situ tensile tests. Comparing experiment
with various models of intergranular interaction, it was found that the
Eshelby-Kr\""oner model correctly approximates the X-ray stress factors (XSFs)
for different reflections hkl and scattering vector orientations. The verified
XSFs were used to investigate the evolution of the first and second-order
stresses in both austenitic and ferritic steels. It was shown that considering
only the elastic anisotropy, the non-linearity of $\sin^2{\psi}$ plots cannot
be explained by crystallographic texture. Therefore, a more advanced method
based on elastic-plastic self-consistent modeling (EPSC) is required for the
analysis. Using such methodology the non-linearities of $\cos^2{\phi}$ plots
were explained, and the evolutions of the first and second-order stresses were
determined. It was found that plastic deformation of about 1- 2% can completely
exchange the state of second-order plastic incompatibility stresses.",2306.03804v1
2023-06-26,Microscopic conductivity of passive films on ferritic stainless steel for hydrogen fuel cells,"Hydrogen fuel cells offer a clean and sustainable energy conversion solution.
The bipolar separator plate, a critical component in fuel cells, plays a vital
role in preventing reactant gas cross-contamination and facilitating efficient
ion transport in a fuel cell. High chromium ferritic stainless steel with an
artificially formed thin chromium oxide passive film has recently gained
attention due to its superior electrical conductivity and corrosion resistance,
making it a suitable material for separators. In this study, we investigate the
microscopic electrical conductivity of the intrinsic passive oxide film on such
ferritic stainless steel. Through advanced surface characterization techniques
such as current sensing atomic force microscopy and scanning tunneling
microscopy/spectroscopy, we discover highly conductive regions within the film
that vary depending on location. These findings provide valuable insights into
the behavior of the passive oxide film in fuel cells. By understanding the
microscopic electrical properties, we can enhance the design and performance of
separator materials in hydrogen fuel cells. Ultimately, this research
contributes to a broader understanding of separator materials and supports the
wider application of hydrogen fuel cells.",2306.14513v1
2024-01-08,Theory of x-ray absorption spectroscopy for ferrites,"The theoretical calculation of the interaction of electromagnetic radiation
with matter remains a challenging problem for contemporary $ab$ $initio$
electronic structure methods, in particular for x-ray spectroscopies. This is
not only due to the strong interaction between the core-hole and the
photo-excited electron, but also due to the elusive multiplet effects that
arise from the Coulomb interaction among the valence electrons. In this work we
report a method based on density-functional theory in conjunction with
multiplet ligand-field theory to investigate various core-level spectroscopies,
in particular x-ray absorption spectroscopy (XAS) and x-ray magnetic circular
dichroism (XMCD). The developed computational scheme is applied to the
$L_{2,3}$ XAS edges of magnetite (Fe$_3$O$_4$) as well as cobalt ferrite
(CoFe$_2$O$_4$) and nickel ferrite (NiFe$_2$O$_4$) and the corresponding XMCD
spectra. The results are in overall good agreement with experimental
observations, both regarding the XAS $L_2$/$L_3$ branching ratio, the peak
positions as well as the relative intensities. The agreement between theory and
experiment is equally good for XAS and the XMCD spectra, for all studied
systems. The results are analyzed in terms of $e_g$ and $t_{2g}$ orbitals
contributions and the importance of optimizing the Slater parameters. The
analysis also highlights the strong effect of the $2p$-$3d$ interaction in
x-ray spectroscopy.",2401.03858v1
2024-01-21,"HARDCORE: H-field and power loss estimation for arbitrary waveforms with residual, dilated convolutional neural networks in ferrite cores","The MagNet Challenge 2023 calls upon competitors to develop data-driven
models for the material-specific, waveform-agnostic estimation of steady-state
power losses in toroidal ferrite cores. The following HARDCORE (H-field and
power loss estimation for Arbitrary waveforms with Residual, Dilated
convolutional neural networks in ferrite COREs) approach shows that a residual
convolutional neural network with physics-informed extensions can serve this
task efficiently when trained on observational data beforehand. One key
solution element is an intermediate model layer which first reconstructs the bh
curve and then estimates the power losses based on the curve's area rendering
the proposed topology physically interpretable. In addition, emphasis was
placed on expert-based feature engineering and information-rich inputs in order
to enable a lean model architecture. A model is trained from scratch for each
material, while the topology remains the same. A Pareto-style trade-off between
model size and estimation accuracy is demonstrated, which yields an optimum at
as low as 1755 parameters and down to below 8\,\% for the 95-th percentile of
the relative error for the worst-case material with sufficient samples.",2401.11488v2
2024-02-23,Effect of temperature and copper doping on the heterogeneous Fenton-like activity of Cu$_x$Fe$_{3-x}$O$_4$ nanoparticles,"Ferrite nanoparticles serve as potent heterogeneous Fenton-like catalysts,
producing reactive oxygen species (ROS) for decomposing organic pollutants. We
investigated the impact of temperature and copper content on the catalytic
activity of nanoparticles with different oxidation states of iron. Via
solvothermal synthesis, we fabricated copper-doped magnetite
(Cu$_x$Fe$_{3-x}$O$_4$) with a Fe$^{2+}$/Fe ratio ~0.33 for the undoped system.
Using a microwave-assisted method, we produced copper-doped oxidized ferrites,
yielding a Fe$^{2+}$/Fe ratio of ~0.11 for the undoped nanoparticles. The ROS
generated by the catalyst were identified and quantified by electron
paramagnetic resonance, while optical spectroscopy allowed us to evaluate its
effectiveness for the degradation of a model organic dye. At room temperature,
the magnetite nanoparticles exhibited the most $\cdot$OH radical production and
achieved almost 90% dye discoloration in 2 hours. This efficiency decreased
with increasing Cu concentration, concurrently with a decrease in $\cdot$OH
generation. Conversely, above room temperature, Cu-doped nanoparticles
significantly enhance the dye degradation, reaching 100% discoloration at
90$^\circ$C. This enhancement is accompanied by a systematic increase in the
kinetic constants, obtained from reaction equations, with Cu doping. This study
highlights the superior stability and high-temperature catalytic advantages of
copper ferrite holding promise for enhancing the performance of nanocatalysts
for decomposing organic contaminants.",2402.15338v1
2008-11-22,Flexomagnetoelectric effect in bismuth ferrite,"There is a profound analogy between inhomogeneous magnetoelectric effect in
multiferroics and flexoelectric effect in liquid crystals. This similarity
gives rise to the flexomagnetoelectric polarization induced by spin modulation.
The theoretical estimations of flexomagnetoelectric polarization agree with the
value of jumps of polarization in magnetoelectric dependences (~20muC/m^2)
observed at spin cycloid suppression at critical magnetic field 200kOe.",0811.3677v1
2014-01-08,Mechanical behavior of steels: from fundamental mechanisms to macroscopic deformation,"My scientific activities aim at understand and predict the mechanical
behaviour of steels, from fundamental mechanisms to macroscopic deformation.
This manuscript is dedicated to the TWIP effect (TWinning Induced Plasticity)
of high manganese austenitic steels and DP effect (Dual-Phase) in more
conventional Ferrite-Martensite steels.",1401.2099v1
2017-01-31,Heterodiffusion coefficients in α-iron,"The diffusion of tungsten in {\alpha}-iron is important for the application
of ferritic-iron alloys to thermal power plants. These data, over a wide
temperature range across the Curie temperature, have been recently reported. We
show that these diffusion coefficients can be satisfactory reproduced in terms
of the bulk elastic and expansivity data by means of a thermodynamical model
that interconnects point defects parameters with bulk qualities.",1701.08993v1
2020-12-28,"Structural, optical and magnetic properties of nanostructured Cr-substituted Ni-Zn spinel ferrites synthesized by a microwave combustion method","Nanoparticles of Cr3+-substituted Ni-Zn ferrites with a general formula
Ni0.4Zn0.6-xCrxFe2O4 (x = 0.0 - 0.6) have been synthesized via a facile
microwave combustion route. The crystalline phase has been characterized by
XRD, TEM, FT-I and XPS revealing the spinel ferrite structure without extra
phases. Crystallite sizes of 23 - 32 nm as estimated by XRD analyses, after
corrections for crystal stains by Williamson-Hall method, are comparable to the
average particle sizes observed by TEM which indicates successfully synthesized
nanocrystals. Rietveld refinement analyses of the XRD patterns have inferred a
monotonic decrease behavior of the lattice parameter with Cr doping in
agreement with Vegard's law of solid solution series. Furthermore, cations
distribution with an increased inversion factor indicate the B-site preference
of Cr3+ ions. The oxidation states and cations distribution indicated by XPS
results imply the Cr3+ doping on the account of Zn2+ ions and a partial
reduction of Fe3+ to Fe2+ to keep the charge balance in a composition series of
(Ni2+)0.4(Zn2+, Cr3+)0.6(Fe2+, Fe3+)2(O2-)4. The optical properties were
explored by optical UV-Vis spectroscopy indicating allowed direct transitions
with band gap energy that decreases from 3.9 eV to 3.7 eV with Cr doping.
Furthermore, the photocatalytic activity for the degradation of methyl orange
(MO) dye was investigated showing largely enhanced photodecomposition up to 30%
of MO dye over Ni0.4Cr0.6Fe2O4 for 6 hours. A vibrating sample magnetometry
(VSM) measurements at room temperature show further enhancement in the
saturation magnetization of Ni0.4Zn0.6Fe2O4 , the highest in Ni-Zn ferrites,
from about 60 to 70 emu/g with the increase of Cr concentration up to x = 0.1,
while the coercivity shows a general increase in the whole range of Cr doping.",2012.14232v1
2022-03-22,"Effect of ECAP and heat treatment on mechanical properties, stress relaxation behavior and corrosion resistance of a 321-type austenitic steel with increased delta-ferrite content","Hot rolled commercial metastable austenitic steel 0.8C-18Cr-10Ni-0.1Ti
(Russian industrial name 08X18H10T, analog 321L) with strongly elongated thin
delta-ferrite particles in its microstructure was the object of investigations.
The lengths of these delta-particles were up to 500 mkm, the thickness was 10
mkm. The formation of the strain-induced martensite as well as the grinding of
the austenite and of the delta-ferrite grains take place during ECAP. During
the annealing of the UFG steel, the formation of the delta-phase particles
takes place. These particles affect the grain boundary migration and the
strength of the steel. However, a reduction of the Hall-Petch coefficient as
compared to the coarse-grained (CG) steel due to the fragmentation of the
delta-ferrite particles was observed. The samples of the UFG steel were found
to have 2-3 times higher stress relaxation resistance as compared to the CG
steel (a higher macroelasticity stress and a lower stress relaxation
magnitude). The differences in the stress relaxation resistance of the UFG and
CG steels were investigated. ECAP was shown to result in an increase in the
corrosion rate and in an increased tendency to the intergranular corrosion
(IGC). The reduction of the corrosion resistance of the UFG steel was found to
originate from the increase in the fraction of the strain-induced martensite
during ECAP.",2203.12102v1
2001-04-27,Faraday rotation spectra of bismuth-substituted ferrite garnet films with in-plane magnetization,"Single crystalline films of bismuth-substituted ferrite garnets have been
synthesized by the liquid phase epitaxy method where GGG substrates are dipped
into the flux. The growth parameters are controlled to obtain films with
in-plane magnetization and virtually no domain activity, which makes them
excellently suited for magnetooptic imaging. The Faraday rotation spectra were
measured across the visible range of wavelengths. To interprete the spectra we
present a simple model based on the existence of two optical transitions of
diamagnetic character, one tetrahedral and one octahedral. We find excellent
agreement between the model and our experimental results for photon energies
between 1.77 and 2.53 eV, corresponding to wavelengths between 700 and 490 nm.
It is shown that the Faraday rotation changes significantly with the amount of
substituted gallium and bismuth. Furthermore, the experimental results suggest
that the magnetooptic response changes linearly with the bismuth substitution.",0104536v3
2003-07-10,Theory of low frequency magnetoelectric coupling in magnetostrictive-piezoelectric bilayers,"A theoretical model is presented for low-frequency magnetoelectric (ME)
effects in bilayers of magnetostrictive and piezoelectric phases. A novel
approach, the introduction of an interface coupling parameter k, is proposed
for the consideration of actual boundary conditions at the interface. An
averaging method is used to estimate effective material parameters. Expressions
for ME voltage coefficients are obtained by solving elastostatic and
electrostatic equations. We consider both unclamped and rigidly clamped
bilayers and three different field orientations of importance: (i) longitudinal
fields in which the poling field, bias field and ac fields are all parallel to
each other and perpendicular to the sample plane; (ii) transverse fields for
magnetic fields parallel to each other and perpendicular to electric fields,
and (iii) in-plane longitudinal fields for all the fields parallel to each
other and to the sample plane. The theory predicts a giant ME coupling for
bilayers with cobalt ferrite (CFO), nickel ferrite (NFO), or lanthanum
strontium manganite (LSMO) for the magnetostrictive phase and barium titanate
(BTO) or lead zirconate titanate (PZT) for the piezoelectric phase.",0307264v1
2004-07-01,Universal transport properties of open microwave cavities with and without time-reversal symmetry,"We measure the transmission through asymmetric and reflection-symmetric
chaotic microwave cavities in dependence of the number of attached wave guides.
Ferrite cylinders are placed inside the cavities to break time-reversal
symmetry. The phase-breaking properties of the ferrite and its range of
applicability are discussed in detail. Random matrix theory predictions for the
distribution of transmission coefficients T and their energy derivative dT/dE
are extended to account for absorption. Using the absorption strength as a
fitting parameter, we find good agreement between universal transmission
fluctuations predicted by theory and the experimental data.",0407046v1
2005-02-15,Influence of strain and oxygen vacancies on the magnetoelectric properties of multiferroic bismuth ferrite,"The dependencies on strain and oxygen vacancies of the ferroelectric
polarization and the weak ferromagnetic magnetization in the multiferroic
material bismuth ferrite, BiFeO_3, are investigated using first principles
density functional theory calculations. The electric polarization is found to
be rather independent of strain, in striking contrast to most conventional
perovskite ferroelectrics. It is also not significantly affected by oxygen
vacancies, or by the combined presence of strain and oxygen vacancies. The
magnetization is also unaffected by strain, however the incorporation of oxygen
vacancies can alter the magnetization slightly, and also leads to the formation
of Fe^{2+}. These results are discussed in light of recent experiments on
epitaxial films of BiFeO_3 which reported a strong thickness dependence of both
magnetization and polarization.",0502364v1
2006-06-01,Microstructural characterization and kinetics modelling of vermicular cast irons,"Several experimental techniques are used for phase identification and
microstructure characterization of austempered vermicular cast irons (XRD, SEM,
TEM and Mossbauer spectroscopy). Acicular structures were found to be composed
by ferrite and austenite with average sizes compatible with those reported for
bainitic ferrite in steels and Austempered Ductile Iron. An assessment of the
free energy change involved in the austenite to bainite transformation assuming
a plate-like nucleation shape for bainite gave an average characteristic length
close to the observed from statistical length distributions. The kinetics of
the transformation was modelled in the Avrami framework; both the diffusion
controlled and the diffusionless growth hypothesis were considered in order to
elucidate the mechanism underlying the austempering phase transformation.
Results indicated that diffusion of C is the responsible of the nucleation
process of the bainite sheaves, that appear as a consequence of a localized
displacive transformation when the C concentration is adequate, but further
growth of the bainite plates is almost suppressed.",0606031v2
2006-08-07,Electronic structure of normal and inverse spinel ferrites from first principles,"We apply the self-interaction corrected local spin density %(SIC-LSD)
approximation to study the electronic structure and magnetic properties of the
spinel ferrites MnFe$_{2}$O$_{4}$, Fe$_{3}$O$_{4}$, CoFe$_{2}$O$_{4}$, and
NiFe$_{2}$O$_{4}$. We concentrate on establishing the nominal valence of the
transition metal elements and the ground state structure, based on the study of
various valence scenarios for both the inverse and normal spinel structures for
all the systems. For both structures we find all the studied compounds to be
insulating, but with smaller gaps in the normal spinel scenario. On the
contrary, the calculated spin magnetic moments and the exchange splitting of
the conduction bands are seen to increase dramatically when moving from the
inverse spinel structure to the normal spinel kind. We find substantial orbital
moments for NiFe$_{2}$O$_{4}$ and CoFe$_{2}$O$_{4}$.",0608168v1
2007-05-20,The beta Phase of Multiferroic Bismuth Ferrite and its beta-gamma Metal-Insulator Transition,"We show that epitaxial (001) thin films of multiferroic bismuth ferrite
BiFeO3 are monoclinic at room temperature instead of tetragonal or Rhombohedral
as reported earlier . We report a orthorhombic order-disorder beta-phase
between 820C and 950C contrary to the earlier report. The transition sequence
monoclinic-orthorhombic phase in (001)BiFeO3 thin film
(rhombohedral-orthorhombic transition in single crystal) resembles that of
BaTiO3 or PbSc1/2Ta1/2O3. The transition to the cubic $\gamma$-phase causes an
abrupt collapse of the bandgap toward zero (insulator-metal transition) at the
orthorhombic-cubic beta-gamma transition around 950C. This transition is
similar to the metal-insulator transition in Ba0.6K0.4BiO3.",0705.2883v3
2007-05-27,Influence of pulsed magnetic field on single- and two-pulse nuclear spin echoes in multidomain magnets,"By the method of additional pulsed magnetic field influence in different
magnetic materials (half metals, manganites, lithium ferrite, cobalt) it is
established the analogy of time diagrams of magnetic pulse influence on single-
and two pulse echoes in magnets when the distortion mechanism of single-pulse
echo formation is effective, and the absence of such analogy in the case of
lithium ferrite where the multipulse mechanism of single-pulse echo formation
is effective.
  It is shown also that the timing and frequency diagrams of magnetic pulse
influence on the two-pulse echo signals, corresponding to the symmetric and
asymmetric magnetic pulse applications in the studied magnets, are defined by
their domain walls parameters and could serve for their qualitative and
quantitative characterization.",0705.3979v1
2007-07-20,The Ba2LnFeNb4O15 Tetragonal Tungsten Bronze: towards RT composite multiferroics,"Several Niobium oxides of formula Ba2LnFeNb4O15 (Ln = La, Pr, Nd, Sm, Eu, Gd)
with the Tetragonal Tungsten Bronze (TTB) structure have been synthesised by
conventional solid-state methods. The Neodymium, Samarium and Europium
compounds are ferroelectric with Curie temperature ranging from 320 to 440K.
The Praseodymium and Gadolinium compounds behave as relaxors below 170 and 300
K respectively. The Praseodymium, Neodymium, Samarium, Europium and Gadolinium
compounds exhibit magnetic hysteresis loops at room temperature originating
from traces of a barium ferrite secondary phase. The presence of both
ferroelectric and magnetic hysteresis loops at room temperature allows
considering these materials as composites multiferroic. Based on
crystal-chemical analysis we propose some relationships between the
introduction of Ln3+ ions in the TTB framework and the chemical, structural and
physical properties of these materials.",0707.3112v2
2008-08-08,Spectral properties of interacting magnetoelectric particles,"The linear magnetoelectric (ME) effect provides a special route for linking
magnetic and electric properties. In microwaves, a local ME effect appears due
to the dynamical symmetry breakings of magnetic-dipolar modes (MDMs) in a
ferrite disk particle. The fact that for MDMs in a ferrite disk one has evident
both classical and quantum-like attributes, puts special demands on the methods
used for study of interacting ME particles. A proper model for coupled
particles should be based on the spectral characteristics of MDM oscillations
and an analysis of the overlap integrals for interacting eigen oscillating ME
elements. In this paper, we present theoretical studies of spectral properties
of literally coupled of MDM ME disks. We show that there exists the ""exchange""
mechanism of interaction between the particles, which is distinctive from the
magnetostatic interaction between magnetic dipoles. The spectral method
proposed in this paper may further the development of a theory of ME
""molecules"" and realization of local ME composites.",0808.1198v1
2009-05-08,A simple route to a tunable electromagnetic gateway,"Transformation optics is used to design a gateway that can block
electromagnetic waves but allows the passage of other entities. Our conceptual
device has the advantage that it can be realized with simple materials and
structural parameters and can have a reasonably wide bandwidth. In particular,
we show that our system can be implemented by using a magnetic photonic crystal
structure that employs a square ray of ferrite rods, and as the field response
of ferrites can be tuned by external magnetic fields, we end up with an
electromagnetic gateway that can be open or shut using external fields. The
functionality is also robust against the positional disorder of the rods that
made up the photonic crystal.",0905.1273v1
2010-06-25,Epitaxial strain effects in the spinel ferrites CoFe2O4 and NiFe2O4 from first principles,"The inverse spinels CoFe2O4 and NiFe2O4, which have been of particular
interest over the past few years as building blocks of artificial multiferroic
heterostructures and as possible spin-filter materials, are investigated by
means of density functional theory calculations. We address the effect of
epitaxial strain on the magneto-crystalline anisotropy and show that, in
agreement with experimental observations, tensile strain favors perpendicular
anisotropy, whereas compressive strain favors in-plane orientation of the
magnetization. Our calculated magnetostriction constants $\lambda_{100}$ of
about -220 ppm for CoFe2O4 and -45 ppm for NiFe2O4 agree well with available
experimental data. We analyze the effect of different cation arrangements used
to represent the inverse spinel structure and show that both LSDA+U and GGA+U
allow for a good quantitative description of these materials. Our results open
the way for further computational investigations of spinel ferrites.",1006.5080v1
2010-10-09,Superparamagnetism in Nanocrystalline Copper Ferrite Thin Films,"The rf sputtered copper ferrite films contain nanocrystalline grains. In
these films, the magnetization does not saturate even in high magnetic fields.
This phenomenon of high field susceptibility is attributed to the defects
and/or superparamagnetic grains in the films. A simple model is developed to
describe the observed high field magnetization behavior of these films. The
model is found to fit well to the high field part for all the studied films. An
attempt is also made to explain the temperature variation of the ferrimagnetic
contribution on the basis of reported exchange constants.",1010.1877v1
2010-10-09,The High Field Magnetization in the RF Sputter Deposited Copper Ferrite Thin Films,"Copper ferrite thin films were deposited on amorphous quartz substrates. The
as deposited films were annealed in air and either quenched or slow cooled.
Magnetization studies were carried out on the as deposited as well as annealed
films using a SQUID magnetometer. The M-H curves were measured up to a field of
7T, at temperatures varying from 5K to 300K. The magnetization in the films did
not saturate, even at the highest field. The expression, M(H)= Q(1- a/H^n)
fitted the approach to saturation best with n=1/2, for all films and at all
temperatures. The coefficient a was the highest for the as deposited film and
was the smallest for the quenched film. In the case of as deposited film, the
value of coefficient a increased with increasing temperature, while for the
annealed films, the value of a showed a decrease as temperature increases.",1010.1881v1
2010-10-09,Temperature dependence of Magnetic properties in Nanocrystalline copper ferrite thin films,"The copper ferrite thin films have been deposited by RF sputtering at a 50W
rf power. The As-deposited films are annealed in air at $800^{\circ}$C and then
slow cooled. The As-deposited (AD) as well as slow cooled (SC) films are
studied using a SQUID Magnetometer. The M Vs H curves have been recorded at
various temperatures between 5K to 300K. The coercivities obtained from the MH
curves are then plotted against temperature (T). The magnetization in the films
does not saturate, even at the highest field of 7T. The high field part of the
M Vs H curves is fitted using the H1/2 term of Chikazumi expression M(H)= Q*(1-
a /Hn), with n=1/2. The variation of coefficient 'a' of H1/2 term has been
observed with temperature (T). An attempt has been made to correlate this with
the coercivity (Hc) in the case of annealed films.",1010.1882v1
2011-03-15,Oxygen hyperstoichiometric hexagonal ferrite CaBaFe4O7+δ(δ \approx 0.14) : coexistence of ferrimagnetism and spin glass behavior,"An oxygen hyperstoichiometric ferrite CaBaFe4O7+\delta (\delta \approx 0.14)
has been synthesized using ""soft"" reduction of CaBaFe4O8. Like the oxygen
stoichiometric ferrimagnet CaBaFe4O7, this oxide also keeps the hexagonal
symmetry (space group: P63mc), and exhibits the same high Curie temperature of
270 K. However, the introduction of extra oxygen into the system weakens the
ferrimagnetic interaction significantly at the cost of increased magnetic
frustration at low temperature. Moreover, this canonical spin glass (Tg ~ 166
K) exhibits an intriguing cross-over from de Almeida-Thouless type to
Gabay-Toulouse type critical line in the field temperature plane above a
certain field strength, which can be identified as the anisotropy field. Domain
wall pinning is also observed below 110 K. These results are interpreted on the
basis of cationic disordering on the iron sites.",1103.2939v1
2011-04-08,Magnetic nanocomposites at microwave frequencies,"Most conventional magnetic materials used in the electronic devices are
ferrites, which are composed of micrometer-size grains. But ferrites have small
saturation magnetization, therefore the performance at GHz frequencies is
rather poor. That is why functionalized nanocomposites comprising magnetic
nanoparticles (e.g. Fe, Co) with dimensions ranging from a few nm to 100 nm,
and embedded in dielectric matrices (e.g. silicon oxide, aluminium oxide) have
a significant potential for the electronics industry. When the size of the
nanoparticles is smaller than the critical size for multidomain formation,
these nanocomposites can be regarded as an ensemble of particles in
single-domain states and the losses (due for example to eddy currents) are
expected to be relatively small. Here we review the theory of magnetism in such
materials, and we present a novel measurement method used for the
characterization of the electromagnetic properties of composites with
nanomagnetic insertions. We also present a few experimental results obtained on
composites consisting of iron nanoparticles in a dielectric matrix.",1104.1535v1
2011-06-29,Effect of epitaxial strain on the cation distribution in spinel ferrites CoFe2O4 and NiFe2O4: a density functional theory study,"The effect of epitaxial strain on the cation distribution in spinel ferrites
CoFe2O4 and NiFe2O4 is investigated by GGA+U total energy calculations. We
obtain a very strong (moderate) tendency for cation inversion in NiFe2O4
(CoFe2O4), in agreement with experimental bulk studies. This preference for the
inverse spinel structure is reduced by tensile epitaxial strain, which can lead
to strong sensitivity of the cation distribution on specific growth conditions
in thin films. Furthermore, we obtain significant energy differences between
different cation arrangements with the same degree of inversion, providing
further evidence for recently proposed short range B site order in NiFe2O4.",1106.5887v2
2011-08-13,First Principle Study of Magnetism and Magneto-structural Coupling in Gallium Ferrite,"We report a first-principles study of the magnetic properties, site disorder
and magneto-structural coupling in multiferroic gallium ferrite (GFO) using
local spin density approximation (LSDA+U) of density functional theory. The
calculations of the ground state A-type antiferromagnetic structure predict
magnetic moments consistent with the experiments whilst consideration of
spin-orbit coupling yields a net orbital moment of ~ 0.025 Bohr magneton/Fe
site also in good accordance with the experiments. We find that though site
disorder is not spontaneous in the ground state, interchange between Fe2 and
Ga2 sites is most favored in the disordered state. The results show that
ferrimagnetism in GFO is due to Ga-Fe site disordering such that Fe spins at
Ga1 and Ga2 sites are antiferromagnetically aligned while maintaining
ferromagnetic coupling between Fe spins at Ga1 and Fe1 sites as well as between
Fe spins at Ga2 and Fe2 sites. The effect of spin configuration on the
structural distortion clearly indicates presence of magneto-structural coupling
in GFO.",1108.2773v1
2011-09-29,Ratchet effects for paramagnetic beads above striped ferrite-garnet films,"We calculate the motion of a small paramagnetic bead which is manipulated by
the stripe domain pattern of a ferrite-garnet film. A model for the bead's
motion in a liquid above the film is developed and used to look for ratchet
solutions, where the bead acquires net coherent motion in one direction when
the external field is modulated periodically. We consider three cases. First,
the ratchet, where the beads all go in the same direction. Second, the height
dependent ratchet, where beads at different heights go in opposite direction.
This case can be used to separate beads of different sizes, as considered in J.
Phys. Chem. B 112, 3833 (2008). Third, we describe how the separation threshold
can be tuned by changing the amplitude of the applied field. Finally, we
describe a pseudo ratchet, where the external modulation is not periodic and
the ratchet changes direction periodically.",1109.6491v1
2012-10-02,Magnetic Relaxation in Bismuth Ferrite Micro-Cubes,"The process of magnetic relaxation was studied in bismuth ferrite BiFeO3
multiferroic micro-cubes obtained by means of microwave assisted Pechini
process. Two different mechanisms of relaxation were found. The first one is a
rapid magnetic relaxation driven by the domain reorientations and/or pinning
and motion of domain walls. This mechanism is also responsible for the
irreversible properties at low temperatures. The power-law decay of the
magnetic moment confirms that this relaxation takes place in the system of
weakly interacting ferromagnetic or superferromagnetic domains. The second
mechanism is a longterm weak magnetic relaxation due to spin glass-phase.",1210.0765v1
2012-12-11,Synthesis and Properties of Bismuth Ferrite Multiferroic Nanoflowers,"The method of microwave assisted hydrothermal synthesis of bismuth ferrite
multiferroic nanoflowers, their mechanism of growth, magnetic as well as
dielectric properties are presented. The nanoflowers are composed of numerous
petals formed by BiFeO3 (BFO) nanocrystals and some amount of amorphous phase.
The growth of the nanoflowers begins from the central part of calyx composed of
only few petals towards which subsequent petals are successively attached. The
nanoflowers exhibit enhanced magnetization due to size effect and lack of spin
compensation in the spin cycloid. The dielectric properties of the nanoflowers
are influenced by water confined to crystal nanovoids resulting in a broad
dielectric permittivity maximum at 200 K {\div} 300 K and also by Polomska
transition above the temperature of 450 K.",1212.2538v1
2013-01-09,High coercivity induced by mechanical milling in cobalt ferrite powders,"In this work we report a study of the magnetic behavior of ferrimagnetic
oxide CoFe2O4 treated by mechanical milling with different grinding balls. The
cobalt ferrite nanoparticles were prepared using a simple hydrothermal method
and annealed at 500oC. The non-milled sample presented coercivity of about 1.9
kOe, saturation magnetization of 69.5 emu/g, and a remanence ratio of 0.42.
After milling, two samples attained coercivity of 4.2 and 4.1 kOe, and
saturation magnetization of 67.0 and 71.4 emu/g respectively. The remanence
ratio MR/MS for these samples increase to 0.49 and 0.51, respectively. To
investigate the influence of the microstructure on the magnetic behavior of
these samples, we used X-ray powder diffraction (XPD), transmission electron
microscopy (TEM), and vibrating sample magnetometry (VSM). The XPD analysis by
the Williamson-Hall plot was used to estimate the average crystallite size and
strain induced by mechanical milling in the samples.",1301.1945v1
2013-02-05,Bulk magnetoelectricity in the hexagonal manganites and ferrites,"Improper ferroelectricity (trimerization) in the hexagonal manganites
RMnO$_3$ leads to a network of coupled structural and magnetic vortices that
induce domain wall magnetoelectricity and magnetization neither of which,
however, occurs in the bulk. Here we combined first-principles calculations,
group-theoretic techniques, and microscopic spin models to show how the
trimerization not only induces a polarization but also a bulk magnetization and
bulk magnetoelectric (ME) effect. This results in the existence of a bulk
linear ME vortex structure or a bulk ME coupling such that if direction of
polarization reverses so does magnetization. To measure the predicted ME
vortex, we suggest RMnO$_3$ under large magnetic field. We suggest a family of
materials, the hexagonal RFeO$_3$ ferrites, also display the predicted
phenomena in their ground state.",1302.1099v2
2014-02-06,Controlled growth of bismuth ferrite multiferroic flowers,"This study reports on the synthesis of ball-like bismuth ferrite BiFeO3
nanoflowers by means of microwave assisted hydrothermal process and also on
their composition and mechanism of growth. It turns out that the petals of the
nanoflowers are composed of the nanocrystals with the size about 35-39 nm
whereas their thickness and size depends on the concentration of surfactants.
The petals contain BiFeO3 phase and traces of Bi2O3 oxide and metallic Bi and
Fe deposited mainly at their surface. Amounts of impurity phases are more
pronounced in nanoflowers synthesized during short time, and become almost
negligible for longer microwave processing. The nanoflowers contain also mixed
Fe valence, with the Fe2+/Fe3+ ratio depending on the time of synthesis. The
growth and shape of the nanoflowers result from the process of diffusion in the
initial stages of hydrothermal reaction.",1402.1336v1
2014-04-10,Thermal effect on magnetic parameters of high-coercivity cobalt ferrite,"We prepared very high-coercivity cobalt ferrite nanoparticles using
short-time high-energy mechanical milling. After the milling process, the
coercivity of the nanoparticles reached 3.75 kOe - a value almost five times
higher than that obtained for the non-milled sample. We performed a thermal
treatment on the milled sample at 300, 400, and 600 oC for 30 and 180 mins, and
studied the changes in the magnetic parameters due to the thermal treatment
using the hysteresis curves, Williamson-Hall analysis, and transmission
electron microscopy. The thermal treatment at 600 oC causes a decrease in the
microstructural strain and density of structural defects resulting in a
significant decrease in coercivity. Furthermore, this thermal treatment
increases the size of the nanoparticles and, as a consequence, there is a
substantial increase in the saturation magnetization. The coercivity and the
saturation magnetization are less affected by the thermal treatment at 300 and
400 oC.",1404.2965v1
2014-11-06,Giant magnetodielectric metamaterial,"Dielectric materials with tunable permittivity are highly desirable for
wireless communication, radar technology. However, the tunability of dielectric
properties in the microwave frequency range and higher is an immense challenge
for conventional materials. Here, we demonstrate a giant magnetodielectric
effect in the GHz region in a metamaterial based on ferrite unit cells. The
effect is derived from the coupling of the ferromagnetic resonance and the Mie
resonance in the ferrite unit cells. Both the simulated and experimental
results indicate that the effective permittivity of the metamaterial can be
tuned by modifying the applied magnetic field, and a giant magnetodielectric
effect, [{\epsilon}'(H) - {\epsilon}'(0)]/{\epsilon}'(0) = 15000 % at 11.284
GHz, is obtained. This mechanism offers a promising means of constructing
microwave dielectrics with large tunable ranges and considerable potential for
tailoring via a metamaterial route.",1411.1470v1
2014-11-29,Gyrotropic-nihility state in a composite ferrite-semiconductor structure,"Characteristics of the gyrotropic-nihility state are studied in a
finely-stratified ferrite-semiconductor structure, which is under an action of
an external static magnetic field. Investigations are carried out with the
assistance of the effective medium theory, according to which the studied
structure is approximated as a uniform gyroelectromagnetic medium. The theory
of the gyrotropic-nihility state is developed in terms of the eigenwaves
propagation in such gyroelectromagnetic medium. The frequency and angular
dependencies of the transmittance, reflectance and absorption coefficient are
presented. It turns out that in the frequency band around the frequency of
gyrotropic-nihility state the studied structure appears to be matched to free
space with both the refractive index and the wave impedance which results in
its high transmittance almost in the entire range of angles of the
electromagnetic wave incidence.",1412.0097v1
2015-03-31,Ultrafast near infrared photoinduced absorption in a multiferroic single crystal of bismuth ferrite,"We studied the ultrafast third-order optical nonlinearity in a single crystal
of multiferroic bismuth ferrite (BiFeO3) in the near-infrared range of 0.5-1.0
eV, where the material is fundamentally transparent,at room temperature. With
pump pulses at 1.55 eV, which is off-resonant to the strong inter-band charge
transfer (CT) transition, we observed instantaneous transient absorption with
pencil-like temporal profile originating from the two-photon CT transition from
the oxygen 2p to the iron 3p levels. In contrast, under pumping with 3.10-eV
photons, the pencil-like absorption change was not observed but decay profiles
showed longer time constants. Although the two-photon absorption coefficient is
estimated to be 1.5 cm/GW, which is ten (hundred) times smaller than that of
two(one)-dimensional cuprates, it is larger than those of common semiconductors
such as ZnSe and GaAs at the optical communication wavelength.",1503.08976v1
2015-06-01,Evaluation of (BH)max and magnetic anisotropy of cobalt ferrite nanoparticles synthesized in gelatin,"CoFe2O4 nanoparticles were synthesized using gelatin as a polymerizing agent.
Structural, morphological and magnetic properties of samples treated at
different temperatures were investigated by X-ray diffraction, scanning
electron microscopy, Mossbauer spectroscopy and magnetization measurements. Our
results revealed that the samples annealed at 623 K and temperatures above 973
K have a cation distributions given by (Co0.19Fe0.81)[Co0.81Fe1.19]O4 and
(Co0.06Fe0.94)[Co0.94Fe1.06]O4, respectively. The particle sizes varied from 73
to 296 nm and the magnetocrystalline anisotropy, K1, has values ranging from
2.60x10^6 to 2.71x10^6 J/m3, as determined from the law of approach to
saturation applied to the MxH data at high field. At 5 K, the saturation
magnetization, coercive field and (BH)max varied from 76 to 95 Am2/kg, 479.9 to
278.5 kA/m and 9.7 to 20.9 kJ/m3, respectively. The reported values are in good
agreement with near-stoichiometric cobalt ferrite samples.",1506.00505v1
2015-06-20,Effect of Sintering Temperature on Structural and Magnetic Properties of Ni0.6Zn0.4Fe2O4 Ferrite: Synthesized from Nanocrystalline Powders,"The effect of sintering temperatures (Ts) on the structural and magnetic
properties of Ni0.6Zn0.4Fe2O4 (NZFO) ferrites synthesized by conventional
double sintering method has been reported. The samples are sintered at 1200,
1250 and 1300 {\deg}C. The X-ray diffraction (XRD) analysis reveals the
formation of a single phase cubic spinel structure of the sample. The magnetic
parameters such as saturation magnetization, Ms; coercive field, Hc; remanent
magnetization, Mr and Bohr magneton, {\mu}B are determined and well compared
with reported values. The obtained values are found to be 71.94 emu/gm and 1.2
Oe for Ms and Hc, respectively at Ts=1300 oC. Curie temperature (Tc) at various
Ts has also been calculated. It is noteworthy to note that the sample with a
very low Hc could be used in transformer core and inductor applications.",1506.06280v2
2015-06-25,Topological magnetoelectric effects in microwave far-field radiation,"Similar to electromagnetism, described by the Maxwell equations, the physics
of magnetoelectric (ME) phenomena deals with the fundamental problem of the
relationship between electric and magnetic fields. Despite a formal resemblance
between the two notions, they concern effects of different natures. In general,
ME coupling effects manifest in numerous macroscopic phenomena in solids with
space and time symmetry breakings. Recently it was shown that the near fields
in the proximity of a small ferrite particle with magnetic dipolar mode (MDM)
oscillations have the space and time symmetry breakings and topological
properties of these fields are different from topological properties of the
free space electromagnetic (EM) fields. Such MDM originated fields, called
magnetoelectric (ME) fields, carry both spin and orbital angular momentums.
They are characterized by power flow vortices and non zero helicity. In this
paper, we report on observation of the topological ME effects in far field
microwave radiation based on a small microwave antenna with a MDM ferrite
resonator. We show that the microwave far-field radiation can be manifested
with a torsion structure where an angle between the electric and magnetic field
vectors varies. We discuss the question on observation of the regions of
localized ME energy in far field microwave radiation.",1506.07684v1
2015-08-23,A study of the physical properties of single crystalline Fe5B2P,"Single crystals of Fe5B2P were grown by self-flux growth technique.
Structural and magnetic properties are studied. The Curie temperature of Fe5B2P
is determined to be 655$pm$2K. The saturation magnetization is determined to be
1.72 MuB/Fe at 2K. The temperature variation of the anisotropy constant K1 is
determined for the first time, reaching ~0.50 MJ/m3 at 2K, and it is comparable
to that of hard ferrites. The saturation magnetization is found to be larger
than the hard ferrites. The first principle calculations of saturation
magnetization and anisotropy constant are found to be consistent with the
experimental results.",1508.05629v1
2015-11-04,Numerical Calculations of Wake Fields and Impedances of LHC Collimators' Real Structures,"The LHC collimators have very complicated mechanical designs including
movable jaws made of higly resistive materials, ferrite materials, tiny RF
contacts. Since the jaws are moved very close to the circulating beams their
contribution in the overall LHC coupling impedance is dominant, with respect to
other machine components. For these reasons accurate simulation of collimators'
impedance becomes very important and challenging. Besides, several dedicated
tests have been performed to verify correct simulations of lossy dispersive
material properties, such as resistive wall and ferrites, benchmarking code
results with analytical, semi-analytical and other numerical codes outcomes.
Here we describe all the performed numerical tests and discuss the results of
LHC collimators' impedances and wake fields calculations.",1511.01236v1
2016-02-22,Flexible heat-flow sensing sheets based on the longitudinal spin Seebeck effect using one-dimensional spin-current conducting films,"We demonstrated a flexible thermoelectric (TE) sheet based on the
longitudinal spin Seebeck effect (LSSE) that is especially suitable for
heat-flow sensing applications. This TE sheet contained a Ni0.2Zn0.3Fe2.5O4
film which was formed on a flexible plastic sheet using a spray-coating method
known as ferrite plating. The experimental results suggest that the
ferrite-plated film, which has a columnar crystal structure aligned
perpendicular to the film plane, functions as a unique one-dimensional
spin-current conductor suitable for bendable LSSE-based sensors.",1602.06684v1
2016-02-26,Water dispersible CoFe2O4 nanoparticles with improved colloidal stability for biomedical applications,"Single phase cobalt ferrite (CoFe2O4, CFO) nanoparticles of a controlled size
(~ 6 nm) exhibiting superparamagnetic properties have been synthesized by
hydrothermal technique using oleic acid (OA) as surfactant. The oleic acid
coated CFO nanoparticles are stable in non-polar organic media, such as hexane
but are not well dispersible in water. The surface of these snanoparticles has
been further modified by citric acid using ligand exchange process, which makes
CFO nanoparticles more stable colloidal solution in water. Citric acid coated
CFO nanoparticles exhibits high dispersibility in water, high zeta potential,
very low coercivity and moderate saturation magnetization. Biocompatibility of
these CFO nanoparticles is demonstrated through cytotoxicity test in L929 cell
line.",1602.08415v1
2016-03-16,Molecular dynamics simulation of nanoindentation on nanocomposite pearlite,"We carry out molecular dynamics simulations of nanoindentation to investigate
the effect of cementite size and temperature on the deformation behavior of
nanocomposite pearlite composed of alternating ferrite and cementite layers. We
find that, instead of the coherent transmission, dislocation propagates by
forming a widespread plastic deformation in cementite layer. We also show that
increasing temperature enhances the distribution of plastic strain in the
ferrite layer, which reduces the stress acting on the cementite layer. Hence,
thickening cementite layer or increasing temperature reduces the likelihood of
dislocation propagation through the cementite layer. Our finding sheds a light
on the mechanism of dislocation blocking by cementite layer in the pearlite.",1603.05153v1
2016-07-10,Effect of isothermal holding temperature on the precipitation hardening in Vanadium-microalloyed steels with varying carbon and nitrogen levels,"Combined effect of Carbon and Nitrogen levels and isothermal holding
temperature on the microstructure, precipitation and the tensile properties of
Vanadium microalloyed steels with 0.05 weight percent Vanadium were studied.
Two different Vanadium steels, one having higher Carbon and lower Nitrogen
content, HCLN steel, and the other having lower Carbon and higher Nitrogen
content, LCHN steel, were prepared and subjected to isothermal holding
treatment over a temperature range of 500 to 750 degree Celsius, after
hot-deformation. Maximum precipitation strengthening from fine Vanadium
carbonitride precipitates has been found at intermediate isothermal holding
temperatures i.e. 600 to 650 degree Celsius in both the steels. In spite of the
significantly smaller fraction of pearlite and bainite, coarser average ferrite
grain size and lower interaction of precipitation and dislocation in the
ferrite matrix, the yield strength of LCHN steel was close to HCLN steel. This
can be attributed to the higher precipitation strengthening ranging from 20 to
50 MPa resulted from the finer Vanadium precipitates in LCHN steel than that of
HCLN steel.",1607.02721v1
2016-10-07,Performance Evaluation of Klystron Beam Focusing System with Anisotropic Ferrite Magnet,"A klystron beam focusing system using permanent magnets, which increases
reliability in comparison with electromagnet focusing system, is reported. A
prototype model has been designed and fabricated for a 1.3 GHz, 800 kW klystron
for evaluation of the feasibility of the focusing system with permanent
magnets. In order to decrease the production cost and to mitigate complex
tuning processes of the magnetic field, anisotropic ferrite magnet is adopted
as the magnetic material. As the result of a power test, 798 kW peak output
power was successfully achieved with the prototype focusing system. Considering
a power consumption of the electromagnet focusing system, the required
wall-plug power to produce nominal 800 kW output power with the permanent
magnet system is less than that with electromagnet. However, the power
conversion efficiency of the klystron with the permanent magnet system was
found to be limited by transverse multipole magnetic fields. By decreasing
transverse multipole magnetic field components, especially the dipole and the
quadrupole, the power conversion efficiency would approach to that with
electromagnets.",1610.02130v1
2017-02-20,Effect of annealing on the magnetic properties of zinc ferrite thin films,"We report on the magnetic properties of zinc ferrite thin film deposited on
SrTiO$_3$ single crystal using pulsed laser deposition. X-ray diffraction
result indicates the highly oriented single phase growth of the film along with
the presence of the strain. In comparison to the bulk antiferromagnetic order,
the as-deposited film has been found to exhibit ferrimagnetic ordering with a
coercive field of 1140~Oe at 5~K. A broad maximum, at $\approx$105~K, observed
in zero-field cooled magnetization curve indicates the wide grain size
distribution for the as-deposited film. Reduction in magnetization and blocking
temperature has been observed after annealing in both argon as well as oxygen
atmospheres, where the variation was found to be dependent on the annealing
temperature.",1702.06033v1
2018-11-12,Current direction anisotropy of the spin Hall magnetoresistance in nickel ferrite thin films with bulk-like magnetic properties,"We utilize spin Hall magnetoresistance (SMR) measurements to experimentally
investigate the pure spin current transport and magnetic properties of nickel
ferrite (NiFe2O4,NFO)/normal metal (NM) thin film heterostructures. We use
(001)-oriented NFO thin films grown on lattice-matched magnesium gallate
substrates by pulsed laser deposition, which significantly improves the
magnetic and structural properties of the ferrimagnetic insulator. The NM in
our experiments is either Pt or Ta. A comparison of the obtained SMR magnitude
for charge currents applied in the [100]- and [110]-direction of NFO yields a
change of 50% for Pt at room temperature. We also investigated the temperature
dependence of this current direction anisotropy and find that it is
qualitatively different for the conductivity and the SMR magnitude. From our
results we conclude that the observed current direction anisotropy may
originate from an anisotropy of the spin mixing conductance or of the spin Hall
effect in these Pt and Ta layers, and/or additional spin-galvanic contributions
from the NFO/NM interface.",1811.04696v1
2020-07-28,Magnetic bubbles in an M-type hexagonal ferrite observed by hollow-cone Foucault imaging and small-angle electron diffraction,"We report hollow-cone imaging and small-angle electron diffraction of
nanoscale magnetic textures such as magnetic-striped domains and magnetic
bubbles of M-type hexagonal ferrite
BaFe$_{10.35}$Sc$_{1.6}$Mg$_{0.05}$O$_{19}$. The advantage of the hollow-cone
Foucault method is that magnetic domains with various directions of
magnetization can be visualized under an infocus condition. Moreover, the
contrast of magnetic domain walls in magnetic bubbles depends on the
inclination angle of the illumination beam. The combination of small-angle
electron diffraction and hollow-cone Foucault imaging proves that magnetization
at domain walls exhibits in-plane directions in the magnetic-striped domains
and magnetic bubbles.",2007.13994v1
2016-11-29,Superdirectional Beam of Surface Spin Wave,"The visualized diffraction patterns of surface spin wave excited by
arbitrarily oriented linear transducer are investigated experimentally in the
plane of tangentially magnetized ferrite film for the case where the transducer
length D is much larger than the wavelength L. It is shown experimentally and
theoretically that the angular width of diffracted surface spin wave beam in
anisotropic ferrite film can take values greater or less than L/D and can also
be zero. For the last case superdirectional (nonexpanding) beam of the surface
spin wave is observed experimentally: the smearing of the beam energy along the
film plane is absent and the length of the beam trajectory is maximal (~50 mm).",1611.09595v2
2018-05-10,Maximizing Specific Loss Power for Magnetic Hyperthermia by Hard-Soft Mixed Ferrites,"We report maximized specific loss power and intrinsic loss power approaching
theoretical limits for AC magnetic field heating of nanoparticles. This is
achieved by engineering the effective magnetic anisotropy barrier of
nanoparticles via alloying of hard and soft ferrites. 22 nm
Co0.03Mn0.28Fe2.7O4/SiO2 NPs reached a specific loss power value of 3417
W/gmetal at a field of 33 kA/m and 380 kHz. Biocompatible Zn0.3Fe2.7O4/SiO2
nanoparticles achieved specific loss power of 500 W/gmetal and intrinsic loss
power of 26.8 nHm2/kg at field parameters of 7 kA/m and 380 kHz, below the
clinical safety limit. Magnetic bone cement achieved heating adequate for bone
tumor hyperthermia, incorporating ultralow dosage of just 1 wt% of
nanoparticles. In cellular hyperthermia experiments, these nanoparticles
demonstrated high cell death rate at low field parameters. Zn0.3Fe2.7O4/SiO2
nanoparticles show cell viabilities above 97% at concentrations up to 0.5 mg/ml
within 48 hrs, suggesting toxicity lower than that of magnetite.",1805.04204v1
2011-11-17,Field-induced Magnetic Transition in Cobalt-Ferrite,"We present magnetostriction and magnetization measurements of a cobalt
ferrite Co0.8Fe2.2O4 single crystal. We observe unusual behaviour in the
magnetic hard axis of the single crystal which manifests in a jump of the
magnetization curve at a critical field. This first order magnetization process
(FOMP) which is explained as an anisotropy driven transition is visible at
temperatures lower than 150 K. By analyzing the anisotropy constants we found
that the higher order anisotropy constant K2 dominates the anisotropy energy.
In the magnetostriction measurements the FOMP is clearly visible as a huge jump
in the [111] direction, which can be explained by means of a geometric model.",1111.4027v2
2013-09-27,Constrained non-collinear magnetism in disordered Fe and Fe-Cr alloys,"The development of quantitative models for radiation damage effects in iron,
iron alloys and steels, particularly for the high temperature properties of the
alloys, requires understanding of magnetic interactions, which control the
phase stability of ferritic-martensitic, ferritic, and austenitic steels. In
this work, disordered magnetic configurations of pure iron and Fe-Cr alloys are
investigated using Density Functional Theory (DFT) formalism, in the form of
constrained non-collinear magnetic calculations, with the objective of creating
a database of atomic magnetic moments and forces acting between the atoms. From
a given disordered atomic configuration of either pure Fe or Fe-Cr alloy, a
penalty contribution to the usual spin-polarized DFT total energy has been
calculated by constraining the magnitude and direction of magnetic moments. An
extensive database of non-collinear magnetic moment and force components for
various atomic configurations has been generated and used for interpolating the
spatially-dependent magnetic interaction parameters, for applications in
large-scale spin-lattice dynamics and magnetic Monte-Carlo simulations.",1309.7183v1
2016-08-11,A revisited Johnson-Mehl-Avrami-Kolmogorov model and the evolution of grain-size distributions in steel,"The classical Johnson-Mehl-Avrami-Kolmogorov approach for nucleation and
growth models of diffusive phase transitions is revisited and applied to model
the growth of ferrite in multiphase steels. For the prediction of mechanical
properties of such steels, a deeper knowledge of the grain structure is
essential. To this end, a Fokker-Planck evolution law for the volume
distribution of ferrite grains is developed and shown to exhibit a log-normally
distributed solution. Numerical parameter studies are given and confirm
expected properties qualitatively. As a preparation for future work on
parameter identification, a strategy is presented for the comparison of volume
distributions with area distributions experimentally gained from polished
micrograph sections.",1608.03821v3
2017-06-07,PbTi1-xPdxO3: A New Room-temperature Magnetoelectric Multiferroic Device Material,"There have been a large number of papers on bismuth ferrite (BiFeO3) over the
past few years, trying to exploit its room-temperature magnetoelectric
multiferroic properties. Although these are attractive, BiFeO3 is not the ideal
multiferroic, due to weak magnetization and the difficulty in limiting leakage
currents. Thus there is an ongoing search for alternatives, including such
materials as gallium ferrite (GaFeO3). In the present work we report a
comprehensive study of the perovskite PbTi1-xPdxO3 with 0 < x < 0.3. Our study
includes dielectric, impedance and magnetization measurements, conductivity
analysis and study of crystallographic phases present in the samples with
special attention paid to minor phases, identified as PdO, PbPdO2, and Pd3Pb.
The work is remarkable in two ways: Pd is difficult to substitute into ABO3
perovskite oxides (where it might be useful for catalysis), and Pd is magnetic
under only unusual conditions (under strain or internal electric fields). The
new material, as a PZT derivative, is expected to have much stronger
piezoelectric properties than BiFeO3.",1706.02194v1
2017-07-13,Towards the ab initio based theory of the phase transformations in iron and steel,"Despite of the appearance of numerous new materials, the iron based alloys
and steels continue to play an essential role in modern technology. The
properties of a steel are determined by its structural state (ferrite,
cementite, pearlite, bainite, martensite, and their combination) that is formed
under thermal treatment as a result of the shear lattice reconstruction ""gamma""
(fcc) -> ""alpha"" (bcc) and carbon diffusion redistribution. We present a review
on a recent progress in the development of a quantitative theory of the phase
transformations and microstructure formation in steel that is based on an ab
initio parameterization of the Ginzburg-Landau free energy functional. The
results of computer modeling describe the regular change of transformation
scenario under cooling from ferritic (nucleation and diffusion-controlled
growth of the ""alpha"" phase to martensitic (the shear lattice instability
""gamma"" -> ""alpha""). It has been shown that the increase in short-range
magnetic order with decreasing the temperature plays a key role in the change
of transformation scenarios. Phase-field modeling in the framework of a
discussed approach demonstrates the typical transformation patterns.",1707.04287v1
2017-07-26,"Bismuth Ferrite Dielectric Nanoparticles Excited at Telecom Wavelengths as Multicolor Sources by Second, Third, and Fourth Harmonic Generation","We demonstrate the simultaneous generation of second, third, and fourth
harmonic from a single dielectric Bismuth Ferrite nanoparticle excited by a
telecom fiber laser at 1560 nm. We first characterize the signals associated
with different nonlinear orders in terms of spectrum, excitation intensity
dependence, and relative signal strengths. Successively, on the basis of the
polarization-resolved emission curves of the three harmonics, we discuss the
interplay of susceptibility tensor components at the different orders and we
show how polarization can be used as an optical handle to control the relative
frequency conversion properties.",1707.08451v4
2018-01-04,Properties of polycrystalline nanoparticles with uniaxial and cubic types of magnetic anisotropy of individual grains,"The influence of the crystal structure inhomogeneities on the magnetic
properties of cobalt nanoparticles with different aspect ratio and spherical
nanoparticles of chromium dioxide, cobalt ferrite and magnetite has been
studied by means of numerical simulation. The polycrystalline nanoparticles are
modeled by means of subdivision of the nanoparticle volume into tightly bound
single-crystal granules with randomly distributed directions of the easy
anisotropy axes. The probability of appearance of quasi uniform and vortex
states in sufficiently large assemblies of polycrystalline nanoparticles of
various types have been calculated depending on the nanoparticle diameter. It
is shown that the subdivision of a nanoparticle into single-crystal granules
with different orientations of the easy anisotropy axes substantially reduces
the effective single-domain diameters for particles with uniaxial type of
anisotropy of individual granules. However, for particles with cubic type of
magnetic anisotropy the influence of the crystal structure inhomogeneities on
the equilibrium properties of the particles is not so important even for
magnetically hard cobalt ferrite nanoparticles. It is practically absent for
magnetically soft magnetite nanoparticles.",1801.01266v1
2019-07-01,"Structural phase diagram and magnetic properties of Sc-substituted rare earth ferrites R1-xScxFeO3 (R=Lu, Yb, Er, and Ho)","We have studied the structural stability of Sc-substituted rare earth (R)
ferrites R1-xScxFeO3, and constructed a structural phase diagram for different
R and x. While RFeO3 and ScFeO3 adopt the orthorhombic and the bixbyite
structure respectively, the substituted compound R1-xScxFeO3 may be stable in a
different structure. Specifically, for R0.5Sc0.5FeO3, the hexagonal structure
can be stable for small R, such as Lu and Yb, while the garnet structure is
stable for larger R, such as Er and Ho. The formation of garnet structure of
the R0.5Sc0.5FeO3 compounds which requires that Sc occupies both the rare earth
and the Fe sites, is corroborated by their magnetic properties.",1907.01052v1
2019-07-15,Study of CoFe2O4/CoFe2 nanostructured powder,"We report an experimental study of the CoFe2O4/CoFe2 nanocomposite, a
nanostructured material formed by hard (CoFe2O4) and soft (CoFe2) magnetic
materials. The precursor material, cobalt ferrite (CoFe2O4), was prepared using
the conventional stoichiometric gel-combustion method. The nanocomposite
material was obtained by reducing partially the precursor material using
activated charcoal as reducing agent in air and argon atmospheres, at 800 and
900 C respectively. The magnetic hysteresis loops demonstrate that, in general,
prepared nanocomposite samples display single magnetic behavior, indicating
exchange coupling between the soft and hard magnetic phases. However, for
nanocomposite samples prepared at higher temperatures, the hysteresis
measurements show steps typical of two-phase magnetic behavior, suggesting the
existence of two non-coupled magnetic phases. The studied nanocomposites
presented coercivity (HC) of about 0.7 kOe, which is considerably lower than
the expected value for cobalt ferrite. A huge increase in HC (>440%) and
maximum energy product (about 240%) was obtained for the nanocomposite after
high energy milling processing.",1907.06758v1
2019-07-28,Warren-Averbach line broadening analysis from a time of flight neutron diffractometer,"The well known Warren-Averbach theory of diffraction line profile broadening
is shown to be applicable to time of flight data obtained from a neutron
spallation source. Without modification, the method is applied to two very
different examples; a cold worked ferritic steel and a thermally stressed
alumina-30% SiC composite. Values of root mean square strains averaged over a
range of lengths for the ferritic steel were used to estimate dislocation
densities; values were found to be in good agreement with geometrically
necessary dislocation densities independently measured from similarly
orientated grains measured from electron backscatter diffraction analysis. An
analytical model for the ceramic is described to validate the estimate of root
mean square strain.",1907.12076v1
2019-10-22,"Comment on Crystallite size dependent exchange bias in MgFe2O4 thin films on Si (100), Journal of Applied Physics, volume 124, page 053901, 2018","K. Mallick and P. S. A. Kumar had reported exchange bias effect in Mg-ferrite
thin films, deposited on Si substrate (with a buffer layer of MgO) using Pulsed
Laser Deposition (PLD) technique. The authors had presented the temperature
dependence exchange bias effect, field dependence exchange bias effect and
training effect of a selected Magnesium ferrite thin film of thickness 132 nm.
These studies were followed by the film thickness dependence of exchange bias
effect. However, the data presented for the 132 nm thick film shows mutually
contradicting values in each and every figures. Here, I point out these highly
self-contradicting data in this comment.",1910.10120v1
2018-03-18,Non-reciprocal Components Based on Switched Transmission Lines,"Non-reciprocal components, such as isolators and circulators, are critical to
wireless communication and radar applications. Traditionally, non-reciprocal
components have been implemented using ferrite materials, which exhibit
non-reciprocity under the influence of an external magnetic field. However,
ferrite materials cannot be integrated into IC fabrication processes, and
consequently are bulky and expensive. In the recent past, there has been strong
interest in achieving non-reciprocity in a non-magnetic IC-compatible fashion
using spatio-temporal modulation. In this paper, we present a general approach
to non-reciprocity based on switched transmission lines. Switched transmission
lines enable broadband, lossless and compact non-reciprocity, and a wide range
of non-reciprocal functionalities, including non-reciprocal phase shifters,
ultra-broadband gyrators and isolators, frequency-conversion isolators, and
high-linearity/high-frequency/ultra-broadband circulators. We present a
detailed theoretical analysis of the various non-idealities that impact
insertion loss and provide design guidelines. The theory is validated by
experimental results from discrete-component-based gyrators and isolators, and
a 25GHz circulator fabricated in 45nm SOI CMOS technology.",1803.06690v1
2018-06-25,Ferromagnetism above 1000 K in highly cation-ordered double-perovskite insulator Sr3OsO6,"Magnetic insulators have been intensively studied for over 100 years, and
they, in particular ferrites, are considered to be the cradle of magnetic
exchange interactions in solids. Their wide range of applications include
microwave devices and permanent magnets . They are also suitable for spintronic
devices owing to their high resistivity, low magnetic damping, and
spin-dependent tunneling probabilities. The Curie temperature is the crucial
factor determining the temperature range in which any ferri/ferromagnetic
system remains stable. However, the record Curie temperature has stood for over
eight decades in insulators and oxides (943 K for spinel ferrite LiFe5O8). Here
we show that a highly B-site ordered double-perovskite, Sr2(SrOs)O6 (Sr3OsO6),
surpasses this long standing Curie temperature record by more than 100 K. We
revealed this B-site ordering by atomic-resolution scanning transmission
electron microscopy. The density functional theory (DFT) calculations suggest
that the large spin-orbit coupling (SOC) of Os6+ 5d2 orbitals drives the system
toward a Jeff = 3/2 ferromagnetic (FM) insulating state. Moreover, the Sr3OsO6
is the first epitaxially grown osmate, which means it is highly compatible with
device fabrication processes and thus promising for spintronic applications.",1806.09308v1
2018-06-27,Photocatalytic activity enhancement by addition of lanthanum into the BiFeO3 structure and the effect of synthesis method,"In this paper, the photocatalytic activity of multiferroics BiFeO3 (BFO) and
Bi0.8La0.2FeO3 (BLFO) nanocrystals with two different morphologies which were
synthesized by two different sol-gel (SG) and hydrothermal (HT) methods have
been studied. All the obtained samples were characterized using X-ray
diffractometer, Fourier transform infrared spectroscopy, transmission electron
microscopy, UV-vis spectroscopy and vibrating sample magnetometer. Differential
thermal analysis (DTA) measurements were probed ferroelectric- paraelectric
first-order phase transition (TC) for all samples. Addition of lanthanum
decreases the electric phase transition. For photocatalyst application of
bismuth ferrite, adsorption potential of nanoparticles for methylene blue (MB)
organic dye was evaluated. The doping of La in the BFO structure enhanced the
photocatalytic activity and about 71% degradation of MB dye was obtained under
visible irradiation. The magnetic and ferroelectric properties of BLFO
nanoparticles improve compared to the undoped BiFeO3 nanoparticles. The
non-saturation at high applied magnetic field for as-prepared samples by HT is
related to the size and shape of products. This work not only presents an
effect of lanthanum substitution into the bismuth ferrite structure on the
physical properties of BFO, but also compares the synthesis method and its
influence on the photocatalytic activity and multiferroics properties of all
nanopowders.",1807.03127v1
2018-08-25,"Photocatalytic activity, optical and ferroelectric properties of Bi0.8Nd0.2FeO3 nanoparticles synthesized by sol-gel and hydrothermal methods","In this study, the effects of synthesis method and dopant Neodymium ion on
the ferroelectric properties and photocatalytic activity of bismuth ferrite
were studied. BiFeO3 (BFO) and Bi0.8Nd0.2FeO3 (BNFO) nanoparticles were
prepared through a facile sol-gel combustion (SG) and hydrothermal (HT)
methods. The as-prepared products were characterized by X-ray powder
diffraction (XRD), Furrier transform infrared spectroscopy (FTIR) and
transmission electron microscope (TEM) images. Both nanophotocatalysts have
similar crystal structures, but the SG products have semi-spherical morphology.
On the other hand, HT samples have rod-like morphology. TEM results indicated
that the morphology of products was not affected by the doping process. The
thermal, optical and magnetic properties of nanoparticles were investigated by
thermogravitometry and differential thermal analysis (TG/DTA), UV-vis
spectroscopy, and vibrating sample magnetometer (VSM). The ferroelectric
properties of BNFO nanoparticles were improved compared to the undoped bismuth
ferrite. The photocatalytic activity of as-synthesized nanoparticles was also
evaluated by the degradation of methyl orange (MO) under visible light
irradiation. The photocatalytic activity of nanoparticles prepared via sol-gel
method exhibited a higher photocatalytic activity compared to powders obtained
by hydrothermal method. Also substitution of Nd into the BFO structure
increased the photocatalytic activity of products.",1808.08427v1
2019-04-04,A highly accurate determination of absorbed power during nanomagnetic hyperthermia,"Absorbed power of nanoparticles during magnetic hyperthermia can be well
determined from changes in the quality factor ($Q$ factor) of a resonator, in
which the radiofrequency (RF) absorbent is placed. We present an order of
magnitude improvement in the $Q$ factor measurement accuracy over conventional
methods by studying the switch-on and off transient signals of the resonators.
A nuclear magnetic resonance (NMR) console is ideally suited to acquire the
transient signals and it also allows to employ the so-called pulse
phase-cycling to remove transient artifacts. The improved determination of the
absorbed power is demonstrated on various resonators in the 1-30 MHz range
including standard solenoids and also a birdcage resonator. This leads to the
possibility to detect minute amounts of ferrite nanoparticles which are
embedded in the body and also the amount of the absorbed power. We demonstrate
this capability on a phantom study, where the exact location of an embedded
ferrite is clearly detected.",1904.02360v1
2019-08-01,Size-dependent spatial magnetization profile of manganese-zinc ferrite Mn0.2Zn0.2Fe2.6O4 nanoparticles,"We report the results of an unpolarized small-angle neutron scattering (SANS)
study on Mn-Zn ferrite (MZFO) magnetic nanoparticles with the aim to elucidate
the interplay between their particle size and the magnetization configuration.
We study different samples of single-crystalline MZFO nanoparticles with
average diameters ranging between 8 to 80 nm, and demonstrate that the smallest
particles are homogeneously magnetized. However, with increasing nanoparticle
size, we observe the transition from a uniform to a nonuniform magnetization
state. Field-dependent results for the correlation function confirm that the
internal spin disorder is suppressed with increasing field strength. The
experimental SANS data are supported by the results of micromagnetic
simulations, which confirm an increasing inhomogeneity of the magnetization
profile of the nanoparticle with increasing size. The results presented
demonstrate the unique ability of SANS to detect even very small deviations of
the magnetization state from the homogeneous one.",1908.00343v2
2019-08-07,Fast response of pulsed laser deposited Zinc ferrite thin film as a chemo-resistive gas sensor,"Thin films of ZnFe2O4 deposited by pulsed laser technique are here
demonstrated as one of the interesting materials for sensing of ethanol. The
response transients were fitted well to one-site Langmuir adsorption model.
Activation energies for (I) adsorption and reaction of ethanol and (II)
desorption (i.e. recovery process) of ethanol from zinc ferrite thin film
surface were obtained on the basis of this model. In this paper, we showed the
effect of operating temperature and gas-concentration on the response time of
thin film sensor materials. At the operating temperature 340oC, the ZnFe2O4
thin film showed high (84%) as well as immediate response to 500 ppm of
ethanol, with its resistance being saturated within ~12 seconds, which stands
far superior to the response time of nano crystalline powders. Those films were
also observed to have a good repeatability of their sensor response, thus
representing a major step towards low-cost large-scale production of this class
of devices.",1908.02780v1
2021-06-21,A low-loss ferrite circulator as a tunable chiral quantum system,"Ferrite microwave circulators allow one to control the directional flow of
microwave signals and noise, and thus play a crucial role in present-day
superconducting quantum technology. They are typically viewed as a black-box,
and their internal structure is not specified, let alone used as a resource. In
this work, we demonstrate a low-loss waveguide circulator constructed with
single-crystalline yttrium iron garnet (YIG) in a 3D cavity, and analyze it as
a multi-mode hybrid quantum system with coupled photonic and magnonic
excitations. We show the coherent coupling of its chiral internal modes with
integrated superconducting niobium cavities, and how this enables tunable
non-reciprocal interactions between the intra-cavity photons. We also probe
experimentally the effective non-Hermitian dynamics of this system and its
effective non-reciprocal eigenmodes. The device platform provides a test bed
for implementing non-reciprocal interactions in open-system circuit QED.",2106.11283v2
2021-12-23,Control of site occupancy by variation of the Zn and Al content in NiZnAl ferrite epitaxial films with low magnetic damping,"The structural and magnetic properties of Zn/Al doped nickel ferrite thin
films can be adjusted by changing the Zn and Al content. The films are
epitaxially grown by reactive magnetron sputtering using a triple cluster
system to sputter simultaneously from three different targets. Upon the
variation of the Zn content the films remain fully strained with similar
structural properties, while the magnetic properties are strongly affected. The
saturation magnetization and coercivity as well as resonance position and
linewidth from ferromagnetic resonance (FMR) measurements are altered depending
on the Zn content in the material. The reason for these changes can be
elucidated by investigation of the x-ray magnetic circular dichroism spectra to
gain site and valence specific information with elemental specificity.
Additionally, from a detailed investigation by broadband FMR a minimum in
g-factor and linewidth could be found as a function of film thickness.
Furthermore, the results from a variation of the Al content using the same set
of measurement techniques is given. Other than for Zn, the variation of Al
affects the strain and even more pronounced changes to the magnetic properties
are apparent.",2112.12456v1
2022-01-12,Magnetic domain wall pinning in cobalt ferrite microstructures,"A detailed correlative structural, magnetic and chemical analysis of
non-stoichiometric cobalt ferrite micrometric crystals was performed by x-ray
magnetic circular dichroism combined with photoemission microscopy, low energy
electron microscopy, and atomic force microscopy. The vector magnetization at
the nanoscale is obtained from magnetic images at different x-ray incidence
angles and compared with micromagnetic simulations, revealing the presence of
defects which pin the magnetic domain walls. A comparison of different types of
defects and the domain walls location suggests that the main source of pinning
in these microcrystals are linear structural defects induced in the spinel by
the substrate steps underneath the islands.",2201.04384v1
2022-01-18,Growth and characterization of ultrathin cobalt ferrite films on Pt(111),"CoFe2O4 thin films (5 nm and 20 nm thick) were grown by oxygen assisted
molecular beam epitaxy on Pt(111) at 523~K and subsequently annealed at 773 K
in vacuum or oxygen. They were characterized in-situ using Auger Electron
Spectroscopy, Low-Energy Electron Diffraction, Scanning Tunneling Microscopy
and Conversion Electron M\""ossbauer Spectroscopy. The as-grown films were
composed of small, nanometric grains. Annealing of the films produced an
increase in the grain size and gave rise to magnetic order at room temperature,
although with a fraction of the films remaining in the paramagnetic state.
Annealing also induced cobalt segregation to the surface of the thicker films.
The measured M\""ossbauer spectra at low temperature were indicative of cobalt
ferrite, the both films showing very similar hyperfine patterns. Annealing in
oxygen or vacuum affected the cationic distribution, which was closer to that
expected for an inverse spinel in the case of annealing in an oxygen
atmosphere.",2201.07087v1
2022-04-15,Experimental Visualization of Dispersion Characteristics of Backward Volume Spin Wave Modes,"Basing on the measurement of spatial spectra (spectra of wavenumbers), the
dispersion characteristics of the first three modes of backward volume spin
wave, propagating along the direction of a constant uniform magnetic field in a
tangentially magnetized ferrite film, were visualized firstly. The study was
carried out by microwave probing of spin waves with subsequent use of spatial
Fourier analysis of the complex wave amplitude for a series of frequencies. It
was found that every m-th mode of the backward volume spins wave can be split
into n satellite modes due to the existence of layers with similar magnetic
parameters in ferrite film. It was found that satellites of the first mode of
this wave are excited most effectively, while satellites of the third mode -
least effectively, and the effectiveness of satellites excitation decreases as
the number n increases. It is found that the theoretical dispersion
dependencies of the first three modes of the wave coincide well with the
experimental dispersion dependencies of the satellite mode that are excited
most effectively.",2204.08293v1
2022-09-19,Ferroelectric Solitons Crafted in Epitaxial Bismuth Ferrite Superlattices,"In ferroelectrics, complex interactions among various degrees of freedom
enable the condensation of topologically protected polarization textures. Known
as ferroelectric solitons, these particle-like structures represent a new class
of materials with promise for beyond CMOS technologies due to their ultrafine
size and sensitivity to external stimuli. Such polarization textures have
scarcely been reported in multiferroics. Here, we report a range of soliton
topologies in bismuth ferrite strontium titanate superlattices. High-resolution
piezoresponse force microscopy and Cs-corrected high-angle annular dark-field
scanning transmission electron microscopy reveal a zoo of topologies, and
polarization displacement mapping of planar specimens reveals center-convergent
and divergent topological defects as small as 3 nm. Phase field simulations
verify that some of these topologies can be classed as bimerons, with a
topological charge of plus and minus one, and first-principles-based effective
Hamiltonian computations show that the co-existence of such structures can lead
to non-integer topological charges, a first observation in a BiFeO3-based
system. Our results open new opportunities in multiferroic topotronics.",2209.08979v1
2022-12-30,Preparation of CuxCe$_{0.3-X}$Ni$_{0.7}$Fe$_2$O$_4$ ferrite nanoparticles as a nitrogen dioxide gas sensor,"In this work, the ferrite nanocomposite CuxCe$_{0.3-X}$Ni$_{0.7}$Fe$_2$O$_4$
is prepared (where: x = 0, 0.05, 0.1, 0.15, 0.2, 0.25) was prepared using the
auto combustion technique (sol-gel), and citric acid was utilized as the fuel
for Auto combustion. The results of X-ray diffraction (XRD), emitting field
scanning electron microscope (FE-SEM), and energy dispersive X-ray analyzer
(EDX) tests revealed that the prepared compound has a face-centered cubic
structure (FCC) polycrystalline, and the lattice constant increases with an
increase in the percentage of doping for the copper ion, and decreases for the
cerium ion and that the compound is porous, and its molecules are spherical,
and there are no additional elements present other than those used in the
synthesis of the compound, indicating that it is of high purity, and the
combination has a high sensitivity to Nitrogen dioxide (NO$_2$) gas, as
determined by the gas detecting equipment.",2212.14861v1
2023-01-26,"Magnetic, Optoelectronic, and Rietveld refined structural properties of Al3+ substituted nanocrystalline Ni-Cu spinel ferrites: An experimental and DFT based study","The nanocrystalline Ni0.7Cu0.3AlxFe2-xO4 (x=0.00: 0.02: 0.10) is prepared
through the sol-gel autocombustion route.Both XRD and Rietveld confirm the
single-phase cubic spinel structure of the investigated materials.Other
structural parameters refined by the Rietveld refinement analysis are
corroborated to single-phase cubic spinel formation of the NPs.Leveraging a
vibrating sample magnetometer (VSM) the consequence of Al3+ substitution on the
magnetic parameters is studied.The saturation magnetization (MS) and Bohr
magneton are found to decrease with Al3+ substitution.The Remanence ratio and
coercivity (HC) are observed to be very low suggesting the materials are soft
ferromagnetic.First-principle calculations were carried out using the density
functional theory (DFT) to demonstrate the optoelectronic behavior of the
materials.The electronic bandgap is found low as Eg=2.99eV for the explored
materials with observing defect states at 0.62eV.The optoelectronic properties
of Al3+ substituted Ni-Cu ferrite NPs have been characterized through the DFT
simulation for the first time, demonstrating their potentiality for
optoelectronic device applications.The materials' optical anisotropy is
observed along the x-axis, which manifests their tunability through
light-matter interaction.",2301.11373v1
2023-01-21,Synthesis and characterization of PEG-coated Zn$_{0.3}$Mn$_x$Fe$_{2.7-x}$O$_4$ nanoparticles as the dual T1/T2-weighted MRI contrast agent,"Super-paramagnetic nanoparticles (NPs) have been widely explored as magnetic
resonance imaging (MRI) contrast agents because of a combination of favorable
magnetic properties, biocompability and ease of fabrication. MRI using
traditional T1- or T2-weighted single mode contrast-enhanced techniques may
yield inaccurate imaging results. In the present work, a T1/T2 dual mode
contrast agent based on the super-paramagnetic zinc-manganese ferrite
(Zn$_{0.3}$Mn$_x$Fe$_{2.7-x}$O$_4$, x= 0, 0.25, 0.75 and 1) NPs with small core
size and a hydrophilic PEG surface coating is reported. The TEM, TGA and FTIR
results confirmed the formation of a uniform coating on the NPs surface. The
MRI analysis revealed that the Zn$_{0.3}$Mn$_{0.5}$Fe$_{2.2}$O$_4$ NPs had the
maximum image contrast compared to other zinc-manganese ferrite samples. Cell
viability evaluations revealed that the coated and uncoated particles did not
inhibit cell growth pattern. The present PEG-coated
Zn$_{0.3}$Mn$_{0.5}$Fe$_{2.2}$O$_4$ NPs can be utilized as a suitable
T1/T2-weighted MRI contrast agent for better diagnostic of abnormalities in the
organs or tissues.",2301.13788v1
2023-02-06,Observation of Coherently Coupled Cation Spin Dynamics in an Insulating Ferrimagnetic Oxide,"Many technologically useful magnetic oxides are ferrimagnetic insulators,
which consist of chemically distinct cations. Here, we examine the spin
dynamics of different magnetic cations in ferrimagnetic NiZnAl-ferrite
(Ni$_{0.65}$Zn$_{0.35}$Al$_{0.8}$Fe$_{1.2}$O$_4$) under continuous microwave
excitation. Specifically, we employ time-resolved x-ray ferromagnetic resonance
to separately probe Fe$^{2+/3+}$ and Ni$^{2+}$ cations on different sublattice
sites. Our results show that the precessing cation moments retain a rigid,
collinear configuration to within $\approx$2$^\circ$. Moreover, the effective
spin relaxation is identical to within $<$10% for all magnetic cations in the
ferrite. We thus validate the oft-assumed ``ferromagnetic-like'' dynamics in
resonantly driven ferrimagnetic oxides, where the magnetic moments from
different cations precess as a coherent, collective magnetization.",2302.03100v1
2023-10-03,Permanent Magnets Based on Hard Ferrite Ceramics,"Permanent magnets are integral components in many of the modern technologies
that are critical for the transition to a sustainable society. However, most of
the high-performance (BHmax > 100 kJ/m3) permanent magnets that are currently
employed contain rare earth elements (REE), which have long been classified as
critical materials with a high supply risk and concerns regarding pollution in
their mining. Therefore, suitable REE-lean/free magnets must be developed in
order to ensure the sustainability of clean energy generation and electric
mobility. The REE-free hexagonal ferrites (or hexaferrites) are the most used
permanent magnets across all applications, with an 85 wt.% pie of the permanent
magnet market. They are the dominant lower-grade option (BHmax < 25 kJ/m3) due
to their relatively good hard magnetic properties, high Curie temperature (>700
K), low cost and good chemical stability. In recent years, the hexaferrites
have also emerged as candidates for substituting REE-based permanent magnets in
applications requiring intermediate magnetic performance (25-100 kJ/m3), due to
considerable performance improvements achieved through chemical tuning,
nanostructuring and compaction/sintering optimization. This chapter reviews the
state-of-the-art sintering strategies being investigated with the aim of
manufacturing hexaferrite magnets with optimized magnetic properties,
identifying key challenges and highlighting the natural future steps to be
followed.",2310.02106v1
2023-10-20,475°C aging embrittlement of partially recrystallized FeCrAl ODS ferritic steels after simulated tube process,"Tube processing and aging effects in FeCrAl ODS steels are investigated in
four mechanical alloyed ferritic ODS steels, Fe15Cr (SP2), Fe15Cr5Al (SP4),
Fe15Cr7Al (SP7) and Fe18Cr7Al (SP11). These steels were made into 0.3mm thick
plates by simulated tube processing (STP). Strengthening after partial
recrystallization was achieved after the last cold rolling and heat treatment
step. However, the ductility reduced about one third of the as-extruded steels.
The STPed steels were aged at 475{\deg}C in sealed vacuum tubes up to 2000 hrs
and 10000 hrs, respectively. The yield stress and elongation were investigated
by tensile tests. The results revealed that all the STPed steels fractured in a
ductile manner irrespective of aging conditions. Aging hardening and ductility
reduction in STPed steels are similar to as-extruded ones. The STPed ODS steels
showed similar ageing embrittlement resistance as as-extruded steels, but much
higher than the non-ODS steels. The aging hardening based on cut-through and
bow-pass mechanisms were discussed. The time dependent hardening of overaged
steel (beta prime only) was analyzed as well.",2310.13842v2
2023-10-24,Complex Poynting vector in gyromagnetic media and its impact on power flow in guided modes,"In this paper, we show the relation between the time-varying spinning nature
of the instantaneous Poynting vector and the phasor form of the complex
Poynting vector in the bulk of the gyromagnetic medium. We show the presence of
a transverse reactive power component in the bulk of the gyrotropic medium,
even for plane wave propagation. We use a simple quantification technique of
Poynting vector spin to analyze the rotation of the instantaneous Poynting
vector using the complex phasor form of the time-averaged Poynting vector. For
a transverse electric mode, we show the similarity between the Poynting vector
spin and the photonic spin of the magnetic field. The Poynting vector spin is
then used to represent the transverse power transfer across a ferrite-air
interface supporting TE surface wave modes. Considering a gyromagnetic
ferrite-filled rectangular waveguide following the TE mode profile, we show the
correspondence between the Poynting vector spin and the overall positive and
backward power flow. We analytically propose a mechanism to engineer the region
of the waveguide supporting backward and forward power propagation.",2310.15867v1
2023-11-03,Effects of Cr content on ion-irradiation hardening of FeCrAl ODS ferritic steels with 9 wt\% Al,"FeCrAl ODS steels for accident tolerant fuel claddings are designed to bear
high-Cr and Al for enhancing oxidation resistance. In this study, we
investigated the effects of Cr content on ion-irradiation hardening of three
ODS ferritic steels with different Cr contents added with 9 wt\% Al, Fe12Cr9Al
(SP12), Fe15Cr9Al (SP13), and Fe18Cr9Al (SP14). The specimens were irradiated
with 6.4MeV Fe\textsuperscript{3+} at 300 \textdegree C to nominal 3 dpa. The
irradiation hardening was measured by nanoindentation method, and the Nix-Gao
plots were used to evaluate the bulk-equivalent hardness. The results showed
that the irradiation hardening decreased with increasing Cr content. The reason
is due to the growth of dislocation loops hindered by solute Cr atoms. TEM
observations showed both $\langle 100\rangle$ and $1/2\langle 111\rangle$
dislocation loops existed in the irradiated area. The irradiation hardening was
estimated by dispersed barrier hardening (DBH) model with dislocation loops.",2311.01879v1
2023-12-08,Strontium Ferrite Under Pressure: Potential Analogue to Strontium Ruthenate,"Despite the significant attention it has garnered over the last thirty years,
the paradigmatic material strontium ruthenate remains the focus of critical
questions regarding strongly correlated materials. As an alternative platform
to unravel some of its perplexing characteristics, we propose to study the
isostructural and more correlated material strontium ferrite. Using density
functional theory combined with dynamical mean-field theory, we attribute the
experimentally observed insulating behavior at zero pressure to strong local
electronic correlations generated by Mott and Hund's physics. At high pressure,
our simulations reproduce the reported insulator-to-metal transition around 18
GPa. Along with distinctive features of a Hund's metal, the resulting metallic
state is found to display an electronic structure analogous to that of
strontium ruthenate, suggesting that it could exhibit similar low-energy
properties.",2312.05314v1
2017-03-17,Rotation and Neoclassical Ripple Transport in ITER,"Neoclassical transport in the presence of non-axisymmetric magnetic fields
causes a toroidal torque known as neoclassical toroidal viscosity (NTV). The
toroidal symmetry of ITER will be broken by the finite number of toroidal field
coils and by test blanket modules (TBMs). The addition of ferritic inserts
(FIs) will decrease the magnitude of the toroidal field ripple. 3D magnetic
equilibria with toroidal field ripple and ferromagnetic structures are
calculated for an ITER steady-state scenario using the Variational Moments
Equilibrium Code (VMEC). Neoclassical transport quantities in the presence of
these error fields are calculated using the Stellarator Fokker-Planck Iterative
Neoclassical Conservative Solver (SFINCS). These calculations fully account for
$E_r$, flux surface shaping, multiple species, magnitude of ripple, and
collisionality rather than applying approximate analytic NTV formulae. As NTV
is a complicated nonlinear function of $E_r$, we study its behavior over a
plausible range of $E_r$. We estimate the toroidal flow, and hence $E_r$, using
a semi-analytic turbulent intrinsic rotation model and NUBEAM calculations of
neutral beam torque. The NTV from the $\rvert n \rvert = 18$ ripple dominates
that from lower $n$ perturbations of the TBMs. With the inclusion of FIs, the
magnitude of NTV torque is reduced by about 75% near the edge. We present
comparisons of several models of tangential magnetic drifts, finding
appreciable differences only for superbanana-plateau transport at small $E_r$.
We find the scaling of calculated NTV torque with ripple magnitude to indicate
that ripple-trapping may be a significant mechanism for NTV in ITER. The
computed NTV torque without ferritic components is comparable in magnitude to
the NBI and intrinsic turbulent torques and will likely damp rotation, but the
NTV torque is significantly reduced by the planned ferritic inserts.",1703.06129v2
2020-01-21,"Mechanical behavior, enhanced dc resistivity, energy band gap and high temperature magnetic properties of Y-substituted Mg-Zn ferrites","We report the synthesis of Y-substituted Mg-Zn ferrites using conventional
standard ceramic technique. XRD patterns confirm the single phase cubic spinel
structure up to x = 0.03 and appearance of a secondary phase of YFeO3for higher
Y contents. FESEM images depict the distribution of grains and EDS spectra
confirmed the absence of any unwanted element. Completion of solid state
reaction and formation of spinel structure has been revealed from FTIR spectra.
The FTIR data along with lattice constant, bulk density and porosity were
further used to calculate the stiffness constant (Cij), elastic constant and
Debye temperatures. Mechanical stability of all studied compositions is
confirmed from Cij using Born stability conditions. Brittleness and isotropic
nature are also confirmed using Poisson ratio and anisotropy constants,
respectively. The enhancement of dc electrical resistivity with Y content is
observed. The energy band gap (increased with Y contents) is found in good
agreement with dc electrical resistivity. Ferrimagnetic to paramagnetic phase
change has been observed from the field dependent high temperature
magnetization curves. The magnetic moments and saturation magnetization were
found to be decreased with increasing temperature. The Curie temperature (Tc)
has been measured from temperature dependent magnetic moment (M-T) and initial
permeability and found to be in good agreement with each other. Decrease in Tc
with Y content is due to redistribution of cations and weakening of the
exchange coupling constant. The magnetic phase transition has been analyzed by
Arrott plot and found to have second order phase transition. The dc resistivity
endorses the prepared ferrites are suitable for high frequency and high
temperature magnetic device applications as well.",2001.07313v1
2020-02-02,A millimeter-wave Bell Test using a ferrite parametric amplifier and a homodyne interferometer,"A combined ferrite parametric amplifier and millimeter-wave homodyne
interferometer are proposed as an ambient temperature Bell Test. It is shown
that the non-linear magnetic susceptibility of the yttrium iron garnet (YIG)
ferrite, on account of its narrow line-width Larmor precessional resonance,
make it an ideal material for the creation of entangled photons. These can be
measured using a homodyne interferometer, as the much larger number of
thermally generated photons associated with ambient temperature emission can be
screened out. The proposed architecture may enable YIG quantum technology-based
sensors to be developed, mimicking in the millimeter-wave band the large number
of quantum optical experiments in the near-infrared and visible regions which
had been made possible by use of the nonlinear beta barium borate
ferroelectric, an analogue of YIG. It is illustrated here how the YIG
parametric amplifier can reproduce quantum optical Type I and Type II wave
interactions, which can be used to create entangled photons in the
millimeter-wave band. It is estimated that when half a cubic centimeter of YIG
crystal is placed in a magnetic field of a few Tesla and pumped with 5 Watts of
millimeter-wave radiation, approximately 0.5x10^12 entangled millimeter-wave
photon pairs per second are generated by the spin-wave interaction. This means
an integration time of only a few tens of seconds is needed for a successful
Bell Test. A successful demonstration of this will lead to novel architectures
of entanglement-based quantum technology room temperature sensors,
re-envisioning YIG as a modern quantum material.",2002.00439v3
2023-02-21,Per-grain and neighbourhood stress interactions during deformation of a ferritic steel obtained using three-dimensional X-ray diffraction,"Three-dimensional X-ray diffraction (3DXRD) has been used to measure,
in-situ, the evolution of $\sim 1800$ grains in a single phase low carbon
ferritic steel sample during uniaxial deformation. The distribution of initial
residual grain stresses in the material was observed to prevail as plasticity
builds, though became less pronounced, and therefore less influential as strain
increased. The initial Schmid factor of a grain was found to be strongly
correlated to the intergranular stress change and the range of stresses that
are permissible; a grain well aligned for easy slip is more likely to exhibit a
range of stresses than those orientated poorly for dislocation motion. The
orientation path of a grain, however, is not only dependent on its initial
orientation, but hypothesised to be influenced by its stress state and the
stress state of its grain environment. A grain neighbourhood effect is
observed: the Schmid factor of serial adjoining grains influences the stress
state of a grain of interest, whereas parallel neighbours are much less
influential. This phenomenon is strongest at low plastic strains only, with the
effect diminishing as plasticity builds. The influence of initial residual
stresses becomes less evident, and grains rotate to eliminate any orientation
dependent load shedding. The ability of the BCC ferrite to exhaust such
neighbourhood interactions, which would otherwise be detrimental in crystal
structures with lower symmetric and fewer slip systems, is considered key to
the high ductility possessed by these materials.",2302.10711v1
2024-02-15,Site-selective cobalt substitution in La-Co co-substituted magnetoplumbite-type ferrites: $^{59}$Co-NMR and DFT calculation study,"The La-Co co-substituted magnetoplumbite-type (M-type) ferrites
$A$Fe$_{12}$O$_{19}$ ($A$ = Ca, Sr and Ba, ion sizes Ca$^{2+}$ $<$ Sr$^{2+}$
$<$ Ba$^{2+}$) with Co compositions around 0.2 have been subjected to
$^{59}$Co-NMR. The results show that Co occupies the 4f$_1$, 2a and 12k sites,
and that the smaller the $A$ ion, the more Co tends to occupy the 4f$_1$
minority spin site, which is effective in enhancing both uniaxial anisotropy
and magnetisation. First-principles total energy calculations based on density
functional theory (DFT) of undoped $A$Fe$_{12}$O$_{19}$ and a supercell ($2
\times 2 \times 1$ of the unit cell) in which 1/96 of Fe$^{3+}$ is replaced by
Co$^{2+}$ were performed to predict the stable structure and Co occupancy
sites. The results show that regardless of $A$, Co is most stable when it
occupies the 4f$_1$ site, followed by the 2a and 12k sites with energy
differences on the order of 100 meV, and Co practically does not occupy the 2b
and 4f$_2$ sites. As the $A$ ion becomes smaller, the energy difference when Co
occupies each Fe site tends to increase, and the Co occupancy of the 4f$_1$
site also increases. The site selectivity of Co can be roughly explained as a
result of the difference in uniaxial strain along the $c$-axis associated with
the difference in $A$. However, the influence of the $A$ ion differs between
the R and S blocks and the local strain also has a secondary effect on the Co
distribution. Based on these results, the guidelines for improving the
performance (anisotropy and magnetisation) of La-Co co-substituted M-type
ferrite magnets with a limited amount of Co can be summarised as follows: It is
effective to select as small $A$ ions as possible and to post-anneal at low
temperature or cool slowly to concentrate Co at the 4f$_1$ site in tetrahedral
coordination.",2402.09706v1
2001-08-10,Magnetism and Electronic Structure in ZnFe$_2$O$_4$ and MnFe$_2$O$_4$,"Density functional calculations are used to study magnetic and electronic
properties of the spinel ferrites, ZnFe$_2$O$_4$ and MnFe$_2$O$_4$. Correct
magnetic orderings are obtained. ZnFe$_2$O$_4$ is predicted to be a small gap
insulator in agreement with experiment. MnFe$_2$O$_4$ is found to be a low
carrier density half-metal in the fully ordered state. However, strong effects
on the electronic structure are found upon partial interchange of Fe and Mn
atoms. This indicates that the insulating character may be due to Anderson
localization associated with the intersite Mn-Fe disorder.",0108176v1
2001-12-04,Numerical comparison of two approaches for the study of phase transitions in small systems,"We compare two recently proposed methods for the characterization of phase
transitions in small systems. The validity and usefulness of these approaches
are studied for the case of the q=4 and q=5 Potts model, i.e. systems where a
thermodynamic limit and exact results exist. Guided by this analysis we discuss
then the helix-coil transition in polyalanine, an example of structural
transitions in biological molecules.",0112050v1
2002-05-02,Current and vortex statistics in microwave billiards,"Using the one-to-one correspondence between the Poynting vector in a
microwave billiard and the probability current density in the corresponding
quantum system probability densities and currents were studied in a microwave
billiard with a ferrite insert as well as in an open billiard. Distribution
functions were obtained for probability densities, currents and vorticities. In
addition the vortex pair correlation function could be extracted. For all
studied quantities a complete agreement with the predictions from the
random-superposition-of-plane-waves approach was obtained.",0205042v1
2006-06-25,Inductive Detection of Magnetostrictive Resonance,"We have developed an inductive method to detect the magnetostrictive
resonance signal and applied it to an ultrasonic magnetostrictive transducer
sample. Slab shaped ferrite samples are mounted in an RF coil and actuated by
pulse modulated RF magnetic field. A DC magnetic field is also applied and the
resonance signal from the sample is detected by the same coil after the RF
field is turned off. The detector system is similar to a conventional pulse NMR
system with quadrature detection. The detected signal is sensitive to the bias
DC field strength and direction as well as the dimension of the sample.",0606636v1
2005-01-06,Booster High-level RF Frequency Tracking Improvement Via Bias-Curve Optimization,"It is important to improve the frequency tracking between the RF drive and
the cavity field for the purpose of reducing longitudinal phase oscillations
and increasing the effective accelerating voltage. And this is especially
beneficial for Booster running at higher intensity with smaller beam emittance.
Optimizing the bias supply current curve for the ferrite tuners can reduce the
phase error between the RF drive and the cavity field, and also improve the
HLRF-to-LLRF frequency tracking efficiency.",0501028v1
2005-01-14,Unidirectional Magnetostatic Waves,"Dispersion characteristics of magnetostatic waves in tangentially magnetized
to saturation ferrite film with a ""magnetic wall"" condition (tangential
component of microwave magnetic field is equal to zero) on the one of the film
surface were calculated. It is found, that unidirectional magnetostatic waves
appear in this geometry: they can transfer energy only in one direction and
fundamentally cannot transfer energy in an opposite direction.",0501074v2
2003-05-12,Comment on Repulsive Casimir Forces,"A recent theoretical calculation shows that the Casimir force between two
parallel plates can be repulsive for plates with nontrivial magnetic properties
(O. Kenneth et al., Phys. Rev. Lett. 89, 033001 (2002)). According to the
authors, the effect may be observed with known materials, such as ferrites and
garnets, and it might be possible to engineer micro- or nanoelectromechanical
systems (MEMS or NEMS) that could take advantage of a short range repulsive
force. Here we show that on the contrary the Casimir force between two parallel
plates in vacuum at micron and submicron distance is always attractive.",0305065v1
2007-11-29,Realization of XNOR and NAND spin-wave logic gates,"We demonstrate the functionality of spin-wave logic XNOR and NAND gates based
on a Mach-Zehnder type interferometer which has arms implemented as sections of
ferrite film spin-wave waveguides. Logical input signals are applied to the
gates by varying either the phase or the amplitude of the spin waves in the
interferometer arms. This phase or amplitude variation is produced by Oersted
fields of dc current pulses through conductors placed on the surface of the
magnetic films.",0711.4720v1
2008-02-20,Electric-field-induced spin-flop in BiFeO3 single crystals at room-temperature,"Bismuth ferrite, BiFeO3, is the only known room-temperature 'multiferroic'
material. We demonstrate here, using neutron scattering measurements in high
quality single crystals, that the antiferromagnetic and ferroelectric orders
are intimately coupled. Initially in a single ferroelectric state, our crystals
have a canted antiferromagnetic structure describing a unique cycloid. Under
electrical poling, polarisation re-orientation induces a spin flop. We argue
here that the coupling between the two orders may be stronger in the bulk than
that observed in thin films where the cycloid is absent.",0802.2915v1
2008-04-21,Unusual magnetic behavior in ferrite hollow nanospheres,"We report unusual magnetic behavior in iron oxide hollow nanospheres of 9.3
$nm$ in diameter. The large fraction of atoms existing at the inner and outer
surfaces gives rise to a high magnetic disorder. The overall magnetic behavior
can be explained considering the coexistence of a soft superparamagnetic phase
and a hard phase corresponding to the highly frustrated cluster-glass like
phase at the surface regions.",0804.3292v1
2008-04-25,Long-range antiferromagnetic interactions in ZnFe2O4 and CdFe2O4,"For the first time, the Fe-Fe interactions in the geometrically frustrated
antiferromagnetic systems of zinc and cadmium ferrites are determined
quantitatively by the first-principles methods of density functional theory.
Both the generalized gradient approximation (GGA) as well as GGA plus the
onesite Coulomb interaction (GGA+U) are considered for the exchange-correlation
energy functional. The interactions up to third neighbours are found to be all
antiferromagnetic for both materials, regardless of which approximation scheme
(GGA or GGA+U) is used. Surprisingly, the thirdneighbour interactions are
estimated to be much stronger than the second-neighbour interactions and on the
same order in magnitude as the first-neighbour interactions.",0804.4059v2
2008-05-07,Design Methodology and Manufacture of a Microinductor,"Potential core materials to supersede ferrite in the 0.5-10 MHz frequency
range are investigated. The performance of electrodeposited nickel-iron,
cobalt-iron-copper alloys and the commercial alloy Vitrovac 6025 have been
assessed through their inclusion within a custom-made solenoid microinductor.
Although the present inductor, at 500 KHz, achieves 77% power efficiency for
24.7W/cm3 power density, an optimized process predicts a power efficiency of
97% for 30.83W/cm3 power density. The principle issues regarding microinductor
design and performance are discussed.",0805.0859v1
2008-11-14,Almeida-Thouless Line in BiFeO3: Is Bismuth Ferrite a mean field spin glass?,"Low-temperature magnetic properties of epitaxial BiFeO3 thin films grown on
(111)-SrTiO3 substrates have been studied. ZFC and FC magnetization curves show
a large discrepency beginning at a characteristic temperature Tf that is
dependent on the magnetic-field strengh. Tf(H) varies according to the well
known de Aleimda-Thouless line (varies in Hexp(2/3)) suggesting an acentric
long rnage spin-glass behavior and mean field system.",0811.2347v1
2008-11-21,Frequency-dependent reflection of spin waves from a magnetic inhomogeneity induced by a surface DC-current,"The reflectivity of a highly localized magnetic inhomogeneity is
experimentally studied. The inhomogeneity is created by a dc-current carrying
wire placed on the surface of a ferrite film. The reflection of propagating
dipole-dominated spin-wave pulses is found to be strongly dependent on the
spin-wave frequency if the current locally increases the magnetic field. In the
opposite case the frequency dependence is negligible.",0811.3491v1
2009-01-18,Generation of pulse trains by current-controlled magnetic mirrors,"The evolution of a spin-wave packet trapped between two direct
current-carrying wires placed on the surface of a ferrite film is observed by
Brillouin light scattering. The wires act as semi-transparent mirrors confining
the packet. Because the spin-wave energy partially passes through these
mirrors, trains of spin-wave packets are generated outside the trap. A
numerical model of this process is presented and applied to the case when the
current in the wires is dynamically controlled. This dynamical control of the
mirror reflectivity provides new functionalities interesting for the field of
spin-wave logic like that of a spin-wave memory cell.",0901.2704v1
2009-01-20,Phase sensitive Brillouin scattering measurements with a novel magneto-optic modulator,"A recently reported phase sensitive Brillouin light scattering technique is
improved by use of a magnetic modulator. This modulator is based on Brillouin
light scattering in a thin ferrite film. Using this magnetic modulator in time-
and space Brillouin light scattering measurements we have increased phase
contrast and excluded influence of optical inhomogeneities in the sample. We
also demonstrate that the quality of the resulting interference patterns can be
improved by data postprocessing using the simultaneously recorded information
about the reference light.",0901.3031v1
2009-02-09,Induced Violation of Time-Reversal Invariance in the Regime of Weakly Overlapping Resonances,"We measure the complex scattering amplitudes of a flat microwave cavity (a
""chaotic billiard""). Time-reversal T-invariance is partially broken by a
magnetized ferrite placed within the cavity. We extend the random-matrix
approach to T-violation in scattering, fit some of the properties of the
scattering amplitudes, and then successfully predict others. Our work
constitutes the most precise test of the theoretical approach to T-violation
within the framework of random-matrix theory so far available.",0902.1418v2
2009-06-26,Relaxation Mechanism for Ordered Magnetic Materials,"We have formulated a relaxation mechanism for ferrites and ferromagnetic
metals whereby the coupling between the magnetic motion and lattice is based
purely on continuum arguments concerning magnetostriction. This theoretical
approach contrasts with previous mechanisms based on microscopic formulations
of spin-phonon interactions employing a discrete lattice. Our model explains
for the first time the scaling of the intrinsic FMR linewidth with frequency,
and 1/M temperature dependence and the anisotropic nature of magnetic
relaxation in ordered magnetic materials, where M is the magnetization. Without
introducing adjustable parameters our model is in reasonable quantitative
agreement with experimental measurements of the intrinsic magnetic resonance
linewidths of important class of ordered magnetic materials, insulator or
metals.",0906.4979v1
2009-07-17,"""Rectifying"" reflection from a magnetic photonic crystal","When an oscillating line source is placed in front of a special mirror
consisting of an array of flat uniformly spaced ferrite rods, half of the image
disappeared at some frequency. We believe that this comes from the coupling to
photonic states of the magnetic surface plasmon band. These states exhibit
giant circulations that only go in one direction due to time reversal symmetry
breaking. Possible applications of this ""rectifying"" reflection include a
robust one-way waveguide, a 90 degree beam bender and a beam splitter, which
are shown to work even in the deep subwavelength scale.",0907.3127v1
2010-01-03,Electrically stabilized magnetic vortex and antivortex states in magnetic dielectrics,"The micromagnetic distribution in a dielectric nanoparticle is theoretically
considered. It is shown that the existence of inhomogeneous magnetoelectric
interaction in magnetic dielectrics provides the possibility to stabilize the
vortex and antivortex state. The estimation of the critical voltage necessary
for vortex/antivortex nucleation in bismuth ferrite and iron garnet
nanoparticles yields a value of +/-150 V. This system can be considered as
electrically switchable two state-logic magnetic element.",1001.0391v4
2011-03-18,Are magnetite (Fe3O4) films on MgAl2O4 auxetic?,"Magnetite (Fe3O4) films were fabricated on MgAl2O4 (001) single crystal
substrates by pulsed laser deposition. In-plane and out-of-plane lattice
constants were determined by X-ray diffraction. The apparent Poisson's ratio
was determined as the negative ratio of the out-of-plane to in-plane strains.
The results show that (i) the determination of Poisson's ratio by this method
is only reliable for fully strained films and (ii) Poisson's ratio = 0.3 along
the <100> direction is positive for this archetypal ferrite. Fe3O4 films grown
on MgAl2O4 (001) are not auxetic.",1103.3666v1
2011-09-09,Modélisation multidomaine du comportement magnéto-mécanique des aciers dual-phases,"The microstructure and mechanical behavior of dual-phase steels are highly
sensitive to the variation of the process (heat treatments). Online control by
magnetic method is relevant. A measurement under applied stress must be
considered. The dual-phase is a two-phase medium (ferrite / martensite). Each
phase can be considered as a sphere embedded in a homogeneous equivalent
medium. The model used for each phase is based on a magneto-mechanical coupled
model. This is an explicit single crystalline model representative of the
behavior of the corresponding phase. Localization rules allow the simulation of
the two-phases medium. Experiments and modeling are compared.",1109.1915v1
2011-10-10,Coaxial Wire Measurements of Ferrite Kicker Magnets,"Fast kicker magnets are used to inject beam into and eject beam out of the
CERN accelerator rings. These kickers are generally transmission line type
magnets with a rectangular shaped aperture through which the beam passes.
Unless special precautions are taken the impedance of the yoke can provoke
significant beam induced heating, especially for high intensities. In addition
the impedance may contribute to beam instabilities. The results of longitudinal
and transverse impedance measurements, for various kicker magnets, are
presented and compared with analytical calculations: in addition predictions
from a numerical analysis are discussed.",1110.2024v1
2012-02-28,An original unified approach for the description of phase tranformations in steel during cooling : first application to binary Fe-C,"Exploiting Landau's theory of phase transformations, defining an original
order parameter and using the phenomenological transformation temperatures, it
is reported that it is possible to describe in a global approach the conditions
for the formation of each phase (ferrite, bainite, martensite) from austenite
during cooling in steel. It allowed to propose a new rigorous classification of
the different thermodynamic conditions controlling each phase tranformation. In
a second step, the approach predicts naturally the effect of cooling rate on
the bainite start temperature. Finally perspectives are assessed to extend the
approach in order to take into account the effect of an external field such as
applied stress.",1202.6194v2
2012-07-04,Phenomenological theory of spin-orbit phase transitions,"This work is devoted to the logical proof of the Goodenough and Khomskii idea
of the existence of spin-orbit transitions in transition magnetic crystals. In
agreement with the basics of the Landau theory of phase transitions the
phenomenological theory of spin-orbit transitions is constructed. The general
scheme of the theory is illustrated by the application to the description of
magnetic and structural transformations in the copper ferrite CuFe2O4.",1207.0899v1
2012-08-10,Resonant features of planar Faraday metamaterial with high structural symmetry,"The transmission of electromagnetic wave through the planar chiral structure,
loaded with the gyrotropic medium on the longitudinal magnetic field is
studied. The frequency dependence of the metamaterial resonance and the angle
of rotation of the polarization plane are obtained. We define both
theoretically and experimentally the range of frequencies and magnetic fields,
where the angle of polarization plane rotation for the metamaterial is
essentially higher than for a single ferrite slab.",1208.2195v2
2013-10-24,Electronic structure and optical band gap determination of NiFe2O4,"In a theoretical study we investigate the electronic structure and the band
gap of the inverse spinel ferrite NiFe2O4. The experimental optical absorption
spectrum is accurately reproduced by fitting the Tran-Blaha parameter in the
modified Becke-Johnson potential. The accuracy of the commonly applied Tauc
plot to find the optical gap is assessed based on the computed spectra and we
find that this approach can lead to a misinterpretation of the experimental
data. The minimum gap of NiFe2O4 is found to be a 1.53eV wide indirect gap,
which is located in the minority spin channel.",1310.6667v1
2013-12-12,Physical and Structural Design of Fast Extraction Kickers for CSNS/RCS,"China Spallation Neutron Source (CSNS) is a high intensity beam facility
being built now in China. Three kicker assemblies, eight pulsed magnets, will
be used in the CSNS rapid circle synchrotron (RCS). The physical and structural
designs of eight kicker magnets that are grouped in 5 different types are
presented. The results of OPERA-3D simulation show that magnet center field
integral meet the physics requirements of design by choosing a suitable magnet
coil structure. Field uniformity for 60% width is +/-0.7%. The ferrite magnet
structure and composition is introduced, and the high voltage feedthrough
design, the installation of six magnets in long vacuum cavity design is
discussed.",1312.3407v1
2014-01-29,Bimodal island size distribution in heteroepitaxial growth,"A bimodal size distribution of two dimensional islands is inferred during
interface formation in heteroepitaxial growth of Bismuth Ferrite on (001)
oriented SrTiO3 by sputter deposition. Features observed by in-situ x-ray
scattering are explained by a model where coalescence of islands determines the
growth kinetics with negligible surface diffusion on SrTiO3. Small clusters
maintain a compact shape as they coalesce, while clusters beyond a critical
size impinge to form large irregular connected islands and a population of
smaller clusters forms in the spaces between the larger ones.",1401.7643v1
2014-04-10,Design and performance of LLRF system for CSNS/RCS,"The rapid cycling synchrotron (RCS) is part of China Spallation Neutron
Source (CSNS). The RCS provides 1.6GeV protons with a repetition rate of 25Hz.
The RF system in RCS is mainly composed of a ferrite loaded RF cavity, a high
power tetrode amplifier, a bias supply of 3300A and a digital low level RF
(LLRF) system based on FPGA. The major challenge of the LLRF system is to solve
problems caused by rapid frequency sweeping and heavy beam loading effect. This
paper will present the design and structure of the LLRF system, and show
results of performance tests.",1404.2658v1
2015-02-04,Instability of a ferrimagnetic state of a frustrated S=1/2 Heisenberg antiferromagnet in two dimensions,"To clarify the instability of the ferrimagnetism which is the fundamental
magnetism of ferrite, numerical-diagonalization study is carried out for the
two-dimensional S=1/2 Heisenberg antiferromagnet with frustration. We find that
the ferrimagnetic ground state has the spontaneous magnetization in small
frustration; due to a frustrating interaction above a specific strength, the
spontaneous magnetization discontinuously vanishes so that the ferrimagnetic
state appears only under some magnetic fields. We also find that, when the
interaction is increased further, the ferrimagnetism disappears even under
magnetic field.",1502.01071v1
2015-05-05,Asymmetric Band Diagrams in Photonic Crystals with a Spontaneous Nonreciprocal Response,"We study the propagation of electromagnetic waves in layered photonic
crystals formed by materials with a spontaneous nonreciprocal response, such as
Tellegen (axion) media or topological insulators. Surprisingly, it is proven
that stratified Tellegen photonic crystals that break simultaneously the space
inversion and time reversal symmetries have always symmetric dispersion
diagrams. Interestingly, we show that by combining chiral and nonreciprocal
materials the photonic band diagrams can exhibit a spectral asymmetry such that
. Furthermore, it is demonstrated that in some conditions two juxtaposed
Tellegen medium layers have an electromagnetic response analogous to that of a
biased ferrite slab.",1505.01200v1
2015-10-24,Graphene Transverse Electric Surface Plasmon Detection using Nonreciprocity Modal Discrimination,"We present a magnetically biased graphene-ferrite structure discriminating
the TE and TM plasmonic modes of graphene. In this structure, the graphene TM
plasmons interact reciprocally with the structure. In contrast, the graphene TE
plasmons exhibit nonreciprocity. This nonreciprocity is manifested in
unidirectional TE propagation in a frequency band close to the interband
threshold frequency. The proposed structure provides a unique platform for the
experimental demonstration of the unusual existence of the TE plasmonic mode in
graphene.",1510.07164v2
2016-06-02,Circulator based on spoof surface plasmon polaritons,"Circulators based on spoof surface plasmon polaritons are designed and
analyzed. In the letter, we use blade structure to realize the propagation of
SSPPs wave and a matching transition is used to feed energy from coplanar
waveguide to the SSPPs. And the circulator shows good nonreciprocal
transmission characteristics. The simulation results indicate that in the
frequency band from 5 to 6.6 GHz, the isolation degree and return loss
basically reaches 15dB and the insertion loss is less than 0.5dB. Moreover, the
use of confinement electromagnetic waves can decrease the size of the ferrite
and show a broadband characteristic.",1606.00567v1
2018-11-19,Photovoltaic effect in multi-domain ferroelectric perovskite oxides,"We propose a device model that elucidates the role of domain walls in the
photovoltaic effect in multi-domain ferroelectric perovskites. The model
accounts for the intricate interplay between ferroelectric polarization, space
charges, photo-generation and electronic transport. When applied to bismuth
ferrite, results show a significant electric potential step across both
71-degree and 109-degree domain walls, which in turn contributes to the
photovoltaic (PV) effect. We also find a strong correlation between
polarization and oxygen octahedra tilts, which indicates the nontrivial role of
the latter in the PV effect. The domain wall-based PV effect is further shown
to be additive in nature, allowing for the possibility of generating
above-bandgap voltage",1811.07948v1
2019-05-24,Photovoltage from ferroelectric domain walls in BiFeO$_3$,"We calculate the component of the photovoltage in bismuth ferrite that is
generated by ferroelectric domain walls, using first-principles methods, in
order to compare its magnitude to the experimentally measured photovoltage. We
find that excitons at the ferroelectric domain walls form an electric dipole
layer resulting in a domain-wall driven photovoltage. This is of the same order
of magnitude as the experimentally measured one, but only if the carrier
lifetimes and diffusion lengths are larger than previously assumed.",1905.10321v2
2019-05-28,"Determination of the magnetic permeability, electrical conductivity, and thickness of ferrite metallic plates using a multi-frequency electromagnetic sensing system","In this paper, an inverse method was developed which can, in principle,
reconstruct arbitrary permeability, conductivity, thickness, and lift-off with
a multi-frequency electromagnetic sensor from inductance spectroscopic
measurements. The system fives the error of ""Bad character(s) in field
Abstract"" for no reason. Please refer to manuscript for the full abstract.",1905.13081v1
2010-05-21,A model of homogeneous semicoherent interphase boundary for heterophase precipitates in substitution alloys under irradiation,"The model of homogeneous semicoherent interphase boundary describes the
processes of absorption and thermoactivated migration of irradiation-produced
inequilibrium point defects at a semicoherent boundary between a heterophase
precipitate and a substitution solid solution. Within this model the kinetics
of evolution of the sizes of precipitates of constant chemical composition
under irradiation is investigated. The results obtained are compared to the
experimental data [I. Monnet et al., J. Nucl. Mater. 335 (2004) 311] for the
ferritic ODS steel EM10+MgO under electron irradiation.",1005.3995v1
2012-01-08,Effect of mechanical stresses on the coercive force of the heterophase non-interacting nanoparticles,"The theoretical analysis of the effect of uniaxial stress on the
magnetization of the system of noninteracting nanoparticles is done by an
example of heterophase particles of maghemite, epitaxially coated with cobalt
ferrite. It is shown that stretching leads to a decrease in the coercive force
$H_c$, and compression leads to its growth. The residual saturation
magnetization $I_{rs}$ of nanoparticles does not change. With increasing of
interfacial exchange interaction, coercive force varies nonmonotonically",1201.1629v1
2012-04-24,"Magnetostatic Spin Waves and Magnetic-Wave Chaos in Ferromagnetic Films. III. Numeric Simulations of Microwave-Band Magnetic Chaos, Its Synchronization and Application to Secure Communication","Selected results of original numeric simulations of non-linear magnetostatic
spin waves and microwave-frequency magnetic chaos in ferrite films are
expounded, as third part of the work whose first two parts are recent arXive
preprints 1204.0200 and 1204.2423 . Especially we consider crucial role of
parametric processes in creating the chaos and simultaneously obstacles to its
synchronization, and examine some possibilities of good enough synchronization
(to an extent allowing its use for direct secure communication in microwave
band).",1204.5410v1
2013-09-28,High-efficiency GHz frequency doubling without power threshold in thin-film Ni81Fe19,"We demonstrate efficient second-harmonic generation at moderate input power
for thin film Ni81Fe19 undergoing ferromagnetic resonance (FMR). Powers of the
generated second-harmonic are shown to be quadratic in input power, with an
upconversion ratio three orders of magnitude higher than that demonstrated in
ferrite. The second harmonic signal generated exhibits a significantly lower
linewidth than that predicted by low-power Gilbert damping, and is excited
without threshold. Results are in good agreement with an analytic, approximate
expansion of the Landau-Lifshitz-Gilbert (LLG) equation.",1309.7483v1
2013-09-18,Observation of plastoferrite character and semiconductor to metal transition in soft ferromagnetic Li0.5Mn0.5Fe2O4ferrite,"We prepared Li0.5Mn0.5Fe2O4 ferrite through chemical reaction in highly
acidic solution and subsequent sintering of chemical routed powder at
temperatures > 800 0C. Surface morphology showed plastoferrite character for
sintering temperature > 1000 0C. Mechanical softening of metal-oxygen bonds at
higher measurement temperatures stimulated delocalization of charge carriers,
which were strongly localized in A and B sites of the spinel structure at lower
temperatures. The charge delocalization process has activated semiconductor to
metallic transition in ac conductivity curves, obeyed by Jonscher power law and
Drude equation, respectively. Metallic state is also confirmed by the frequency
dependence of dielectric constant curves.",1309.7956v1
2020-12-06,Magnetless Circulators Based on Synthetic Angular-Momentum Bias: Recent Advances and Applications,"In this paper, we discuss recent progress in magnet-free non-reciprocal
structures based on a synthetic form of angular momentum bias imparted via
spatiotemporal modulation. We discuss how such components can support metrics
of performance comparable with traditional magnetic-biased ferrite devices,
while at the same time offering distinct advantages in terms of reduced size,
weight, and cost due to the elimination of magnetic bias. We further provide an
outlook on potential applications and future directions based on these
components, ranging from wireless full-duplex communications to metasurfaces
and topological insulators.",2012.03164v1
2012-05-16,Magnetic properties of BiFeO3 micro-cubes synthesized by microwave agitation,"In this report we present results of magnetization measurements and
investigation of aging and memory effect in bismuth ferrite multiferroic
micro-cubes obtained by means of simple microwave synthesis procedure. It is
found that difference between FC and ZFC magnetizations appears at the
temperature of freezing of ferromagnetic domain walls. The decay of the
magnetic moment vs. time described by power-law relation and the absence of
memory effect indicate domain growth mechanism rather than the spin-glass
phase.",1205.3653v1
2020-05-21,Cluster Dynamics Modeling of Niobium and Titanium Carbide Precipitates,"Kinetics of niobium and titanium carbide precipitates in iron has been
simulated with cluster dynamics. The simulations, carried out in austenite and
ferrite for niobium carbides, respectively in austenite for titanium carbide,
were analyzed for dependency on temperature, solute concentration, and initial
cluster distribution. The results are presented for different temperatures and
solute concentrations and compared to available experimental data. They show
little impact of initial cluster distribution beyond a certain relaxation time
and that highly dilute alloys with only monomers present a significantly
different behavior than less dilute alloys or alloys with different initial
cluster distribution.",2005.10574v2
2020-08-31,Power Module (PM) core-specific parameters for a detailed design-oriented inductor model,"This paper obtains shape related parameters and functions of a Power Module
ferrite core which can be required in a design-oriented inductor model, which
is a fundamental tool to design any electronic power converter and its control
policy. Some particular modifications have been introduced into the
standardized method of obtaining characteristics core areas and lengths. Also,
a novel approach is taken to obtain the air gap reluctance as a function of air
gap length for that specific core shape.",2008.13659v3
2020-10-02,Effect of tensile stresses on bainitic isothermal transformation,"The effects of tensile stresses on isothermal bainitic transformation were
studied in the case of a 35MV7 steel. The modification of transformation
kinetics and the presence of transformation plasticity is shown in a first
step. Furthermore the effect of stress on the morphological modifications of
the ferrite laths is illustrated. The role of the stress on these changes is
analysed.",2010.00856v1
2021-06-01,Energetic particle transport in optimized stellarators,"Nine stellarator configurations, three quasiaxisymmetric, three
quasihelically symmetric and three non-quasisymmetric are scaled to ARIES-CS
size and analyzed for energetic particle content. The best performing
configurations with regard to energetic particle confinement also perform the
best on the neoclassical {\Gamma}c metric, which attempts to align contours of
the second adiabatic invariant with flux surfaces. Quasisymmetric
configurations that simultaneously perform well on {\Gamma}c and quasisymmetry
have the best overall confinement, with collisional losses under 3%,
approaching the performance of ITER with ferritic inserts.",2106.00716v1
2022-12-19,Steel Phase Kinetics Modeling using Symbolic Regression,"We describe an approach for empirical modeling of steel phase kinetics based
on symbolic regression and genetic programming. The algorithm takes processed
data gathered from dilatometer measurements and produces a system of
differential equations that models the phase kinetics. Our initial results
demonstrate that the proposed approach allows to identify compact differential
equations that fit the data. The model predicts ferrite, pearlite and bainite
formation for a single steel type. Martensite is not yet included in the model.
Future work shall incorporate martensite and generalize to multiple steel types
with different chemical compositions.",2212.10284v1
2003-05-13,Thermal Remagnetization in Polycrystalline Permanent Magnets,"The thermal remagnetization (TR), i.e. the reentrance of magnetization upon
heating in a steady-field demagnetized sample, is a common feature to the four
types of polycrystalline permanent magnets, mainly utilized for practical
purposes, i.e. barium ferrites, SmCo5, Sm2Co17 and NdFeB magnets. The effect is
small for pinning controlled and large for nucleation controlled magnets. The
effect is strongly dependent on the demagnetization factor and may reach nearly
100 per cent in SmCo5 samples measured in a closed circuit. The TR is very
sensitive to a small superimposed steady field. The maximum effect and the
position of the peak is dependent on the initial temperature. The direction of
the TR is correlated with the temperature coefficient of the coercivity,
resulting in a inverse TR in barium ferrite. The susceptibility of the
thermally remagnetized samples is increased. Repeated cycles of steady-field
demagnetization followed by heating result in the same TR. The phenomenology of
TR and ITR is explained by means of a model taking into account both the
internal field fluctuations due to grain interactions and the decay of single
domain grains into multi-domain state. By taking the measured temperature
dependencies of the coercivity and the saturation magnetization the theory is
able to reproduce the experiments very well, allowing to determine the width of
the field fluctuations, the width of the switching field distribution and an
internal demagnetization factor as characteristics of the materials by fitting.",0305292v1
2005-08-31,Spinel ferrites: old materials bring new opportunities for spintronics,"Over the past few years, intensive studies of ultrathin epitaxial films of
perovskite oxides have often revealed exciting properties like giant
magnetoresistive tunnelling and electric field effects. Spinel oxides appear as
even more versatile due to their more complex structure and the resulting many
degrees of freedom. Here we show that the epitaxial growth of nanometric
NiFe2O4 films onto perovskite substrates allows the stabilization of novel
ferrite phases with properties dramatically differing from bulk ones. Indeed,
NiFe2O4 films few nanometres thick have a saturation magnetization at least
twice that of the bulk compound and their resistivity can be tuned by orders of
magnitude, depending on the growth conditions. By integrating such thin NiFe2O4
layers into spin-dependent tunnelling heterostructures, we demonstrate that
this versatile material can be useful for spintronics, either as a conductive
electrode in magnetic tunnel junctions or as a spin-filtering insulating
barrier in the little explored type of tunnel junction called spin-filter. Our
findings are thus opening the way for the realisation of monolithic spintronics
architectures integrating several layers of a single material, where the layers
are functionalised in a controlled manner.",0508764v1
2009-06-16,Microwave Technologies-- Determination of Magnetic and Dielectric Materials Microwave Properties,"In this study, four different techniques are presented. 1 Rectangular
waveguide measurement technique for normal microwave materials microwave
properties such as permeability and permittivity. This technique removed guess
parameter and dispersive effect issues of the old waveguide measurement
techniques. It projects a new route for determination of any microwave
materials magnetic and dielectric properties without using any guesses. 2
Coaxial probe measurement technique for the liquid and biological tissues
dielectric permittivity. This coaxial probe technique has an advantage which is
to attain the highest reflected signal from the coaxial probe tip, so that it
is a fast and very sensitive technique to differentiate lossy materials
dielectric permittivity. This technique could be useful non destructive
detections for tumors in hospital and non destructive detections for chemical
liquids as well. 3 A microstripline measurement technique for oxides microwave
measurement at low frequency spectra where the waveguide technique becomes
robot and cumbersome. 4 A new methodology is presented for the rectangular
waveguide technique to determine microwave metamaterials refractive index,
permeability and permittivity using the rectangular waveguide. In summary, the
presented techniques are capable enough to determine magnetic and non magnetic
solid state materials, liquids, powders and biological tissues microwave
properties from the broad microwave frequencies spectra between 1 GHz to 50
GHz. Lastly, a special ferrites microwave properties are also presented since
the negative refractive index from the insulator ferrite could be an
interesting subject.",0906.2928v1
2009-10-30,Resonant x-ray scattering in 3d-transition-metal oxides: Anisotropy and charge orderings,"The structural, magnetic and electronic properties of transition metal oxides
reflect in atomic charge, spin and orbital degrees of freedom. Resonant x-ray
scattering (RXS) allows us to perform an accurate investigation of all these
electronic degrees. RXS combines high-Q resolution x-ray diffraction with the
properties of the resonance providing information similar to that obtained by
atomic spectroscopy (element selectivity and a large enhancement of scattering
amplitude for this particular element and sensitivity to the symmetry of the
electronic levels through the multipole electric transitions). Since electronic
states are coupled to the local symmetry, RXS reveals the occurrence of
symmetry breaking effects such as lattice distortions, onset of electronic
orbital ordering or ordering of electronic charge distributions. We shall
discuss the strength of RXS at the K absorption edge of 3d transition-metal
oxides by describing various applications in the observation of local
anisotropy and charge disproportionation. Examples of these resonant effects
are (I) charge ordering transitions in manganites, Fe3O4 and ferrites and (II)
forbidden reflections and anisotropy in Mn3+ perovskites, spinel ferrites and
cobalt oxides. In all the studied cases, the electronic (charge and/or
anisotropy) orderings are determined by the structural distortions.",0910.5789v1
2010-09-17,Investigation of multiple echo signals formation mechanism in magnet at excitation by two arbitrary radio-frequency pulses,"The quantum-mechanical calculations of intensities and time moments of
appearance of multiple spin echo signals of excitation of nuclear spin system
of magnet by two arbitrary width radio-frequency pulses were carried out. This
method was used by us earlier at consideration of multiple-pulse analogs of
single-pulse echo in multidomain magnets upon sudden jumps of the effecting
magnetic field in the rotating coordinate system during the action of
radio-frequency pulse. The formation mechanisms of echo signals are discussed.
The appearance of four primary stimulated echo signals is predicted. The total
number of echo signals at fixed parameters of radio-frequency pulses does not
exceed thirteen ones. Theoretical conclusions are in compliance with
experiments carried out on lithium ferrite. As it was established by us earlier
in this magnetic dielectric, in difference from ferrometals, it is observed
very short relaxation times of single-pulse and two-pulse stimulated echoes,
and the contribution of radio-frequency pulse fronts distribution mechanism is
insignificant. For this reason lithium ferrite is a good material for the
experimental verification of theoretical conclusions in experimental conditions
most close to the theoretical model.",1009.3371v1
2011-03-25,"Electronic Structures, Born Effective Charges and Spontaneous Polarization in Magnetoelectric Gallium Ferrite","We present a theoretical study of the structure-property correlation in
gallium ferrite, based on the first principles calculations followed by a
subsequent comparison with the experiments. Local spin density approximation
(LSDA+U) of the density functional theory has been used to calculate the ground
state structure, electronic band structure, density of states and Born
effective charges. Calculations reveal that the ground state structure is
orthorhombic Pc21n having A-type antiferromagnetic spin configuration, with
lattice parameters matching well with those obtained experimentally. Plots of
partial density of states of constituent ions exhibit noticeable hybridization
of Fe 3d, Ga 4s, Ga 4p and O 2p states. However, the calculated charge density
and electron localization function show largely ionic character of the Ga/Fe-O
bonds which is also supported by lack of any significant anomaly in the
calculated Born effective charges with respect to the corresponding nominal
ionic charges. The calculations show a spontaneous polarization of ~ 59
microC/cm^2 along b-axis which is largely due to asymmetrically placed Ga1,
Fe1, O1, O2 and O6 ions.",1103.4935v2
2011-10-21,Exchange-spring behavior in bimagnetic CoFe2O4/CoFe2 nanocomposite,"In this work we report a study of the magnetic behavior of ferrimagnetic
oxide CoFe2O4 and ferrimagnetic oxide/ferromagnetic metal CoFe2O4/CoFe2
nanocomposites. The latter compound is a good system to study hard
ferrimagnet/soft ferromagnet exchange coupling. Two steps were used to
synthesize the bimagnetic CoFe2O4/CoFe2 nanocomposites: (i) first preparation
of CoFe2O4 nanoparticles using the a simple hydrothermal method and (ii) second
reduction reaction of cobalt ferrite nanoparticles using activated charcoal in
inert atmosphere and high temperature. The phase structures, particle sizes,
morphology, and magnetic properties of CoFe2O4 nanoparticles have been
investigated by X-Ray diffraction (XRD), Mossbauer spectroscopy (MS),
transmission electron microscopy (TEM), and vibrating sample magnetometer (VSM)
with applied field up to 3.0 kOe at room temperature and 50K. The mean diameter
of CoFe2O4 particles is about 16 nm. Mossbauer spectra reveal two sites for
Fe3+. One site is related to Fe in an octahedral coordination and the other one
to the Fe3+ in a tetrahedral coordination, as expected for a spinel crystal
structure of CoFe2O4. TEM measurements of nanocomposite show the formation of a
thin shell of CoFe2 on the cobalt ferrite and indicate that the nanoparticles
increase to about 100 nm. The magnetization of nanocomposite showed hysteresis
loop that is characteristic of the exchange spring systems. A maximum energy
product (BH)max of 1.22 MGOe was achieved at room temperature for CoFe2O4/CoFe2
nanocomposites, which is about 115% higher than the value obtained for CoFe2O4
precursor. The exchange-spring interaction and the enhancement of product
(BH)max in nanocomposite CoFe2O4/CoFe2 have been discussed.",1110.4905v1
2012-03-28,"Geometric and disorder -- type magnetic frustration in ferrimagnetic ""114"" Ferrites: Role of diamagnetic Li+ and Zn2+ cation substitution","The comparative study of the substitution of zinc and lithium for iron in the
""114"" ferrites, YBaFe4O7 and CaBaFe4O7, shows that these diamagnetic cations
play a major role in tuning the competition between ferrimagnetism and magnetic
frustration in these oxides. The substitution of Li or Zn for Fe in the cubic
phase YBaFe4O7 leads to a structural transition to a hexagonal phase
YBaFe4-xMxO7, for M = Li (0.30 < x < 0.75) and for M = Zn (0.40 < x < 1.50). It
is seen that for low doping values i.e. x = 0.30 (for Li) and x = 0.40 (for
Zn), these diamagnetic cations induce a strong ferrimagnetic component in the
samples, in contrast to the spin glass behaviour of the cubic phase. In all the
hexagonal phases, YBaFe4-xMxO7 and CaBaFe4-xMxO7 with M = Li and Zn, it is seen
that in the low doping regime (x ~ 0.3 to 0.5), the competition between
ferrimagnetism and 2 D magnetic frustration is dominated by the average valency
of iron. In contrast, in the high doping regime (x ~ 1.5), the emergence of a
spin glass is controlled by the high degree of cationic disorder, irrespective
of the iron valency.",1203.6220v1
2013-05-02,Chiral properties of bismuth ferrite (BiFeO3) inferred from resonant x-ray Bragg diffraction,"A new chiral phase of ferric ions in bismuth ferrite, the only material known
to support multiferroic behaviour at room temperature, is inferred from
extensive sets of data gathered by resonant x-ray Bragg diffraction. Values of
all ferric multipoles participating in a minimal model of Fe electronic
structure are deduced from azimuthal-angle scans. Extensive sets of
azimuthal-angle data, gathered by resonant x-ray Bragg diffraction, yield
values of all ferric multipoles participating in a minimal model of Fe
electronic structure. Paramagnetic (700 K) and magnetically ordered (300 K)
phases of a single crystal of BiFeO3 have been studied with x-rays tuned near
to the iron K-edge (7.1135 keV). At both temperatures, intensities at a Bragg
spot forbidden in the nominal space-group, R3c, are consistent with a chiral
motif of ferric ions in a circular cycloid propagating along (1, 1, 0)H.
Templeton and Templeton scattering at 700 K is attributed in part to
charge-like quadrupoles in a cycloid. The contribution is not present in a
standard, simplified model of electronic states of the resonant ion with
trivial cylindrical symmetry.",1305.0484v3
2013-10-17,Insights into the Phase Diagram of Bismuth Ferrite from Quasi-Harmonic Free Energy Calculations,"We have used first-principles methods to investigate the phase diagram of
multiferroic bismuth ferrite (BiFeO3 or BFO), revealing the energetic and
vibrational features that control the occurrence of various relevant
structures. More precisely, we have studied the relative stability of four
low-energy BFO polymorphs by computing their free energies within the
quasi-harmonic approximation, introducing a practical scheme that allows us to
account for the main effects of spin disorder. As expected, we find that the
ferroelectric ground state of the material (with R3c space group) transforms
into an orthorhombic paraelectric phase (Pnma) upon heating. We show that this
transition is not significantly affected by magnetic disorder, and that the
occurrence of the Pnma structure relies on its being vibrationally (although
not elastically) softer than the R3c phase. We also investigate a
representative member of the family of nano-twinned polymorphs recently
predicted for BFO [Prosandeev et al., Adv. Funct. Mater. 23, 234 (2013)] and
discuss their possible stabilization at the boundaries separating the R3c and
Pnma regions in the corresponding pressure-temperature phase diagram. Finally,
we elucidate the intriguing case of the so-called super-tetragonal phases of
BFO: Our results explain why such structures have never been observed in the
bulk material, despite their being stable polymorphs of very low energy.
Quantitative comparison with experiment is provided whenever possible, and the
relative importance of various physical effects (zero-point motion, spin
fluctuations, thermal expansion) and technical features (employed
exchange-correlation energy density functional) is discussed. Our work attests
the validity and usefulness of the quasi-harmonic scheme to investigate the
phase diagram of this complex oxide, and prospective applications are
discussed.",1310.4703v1
2014-10-08,Cellular Uptake and Biocompatibility of Bismuth Ferrite Harmonic Advanced Nanoparticles,"Bismuth Ferrite (BFO) nanoparticles (BFO-NP) display interesting optical
(nonlinear response) and magnetic properties which make them amenable for
bio-oriented applications as intra- and extra membrane contrast agents. Due to
the relatively recent availability of this material in well dispersed
nanometric form, its biocompatibility was not known to date. In this study, we
present a thorough assessment of the effects of in vitro exposure of human
adenocarcinoma (A549), lung squamous carcinoma (NCI-H520), and acute monocytic
leukemia (THP-1) cell lines to uncoated and poly(ethylene glycol)-coated BFO-NP
in the form of cytotoxicity, haemolytic response and biocompatibility. Our
results support the attractiveness of the functional-BFO towards biomedical
applications focused on advanced diagnostic imaging.",1410.2068v1
2015-08-31,Wireless Power Transfer for High-precision Position Detection of Railroad Vehicles,"Detection of vehicle position is critical for successful operation of
intelligent transportation system. In case of railroad transportation systems,
position information of railroad vehicles can be detected by GPS, track
circuits, and so on. In this paper, position detection based on tags onto
sleepers of the track is investigated. Position information stored in the tags
is read by a reader placed at the bottom of running railroad vehicle. Due to
limited capacity of battery or its alternative in the tags, power required for
transmission of position information to the reader is harvested by the tags
from the power wirelessly transferred from the reader. Basic mechanism in
wireless power transfer is magnetic induction and power transfer efficiency
according to the relative location of the reader to a tag is discussed with
simulation results. Since power transfer efficiency is significantly affected
by the ferromagnetic material (steel) at the bottom of the railroad vehicle and
the track, magnetic beam shaping by ferrite material is carried out. With the
ferrite material for magnetic beam shaping, degradation of power transfer
efficiency due to the steel is substantially reduced. Based on the experimental
results, successful wireless power transfer to the tag coil is possible when
transmitted power from the reader coil is close to a few watts.",1508.07342v1
2017-08-13,Quantum percolation phase transition and magneto-electric dipole glass in hexagonal ferrites,"Hexagonal ferrites do not only have enormous commercial impact ({\pounds}2
billion/year in sales) due to applications that include ultra-high density
memories, credit card stripes, magnetic bar codes, small motors and low-loss
microwave devices, they also have fascinating magnetic and ferroelectric
quantum properties at low temperatures. Here we report the results of tuning
the magnetic ordering temperature in PbFe$_{12-x}$Ga$_x$O$_{19}$ to zero by
chemical substitution $x$. The phase transition boundary is found to vary as
$T_N \sim (1-x/x_c)^{2/3}$ with $x_c$ very close to the calculated spin
percolation threshold which we determine by Monte Carlo simulations, indicating
that the zero-temperature phase transition is geometrically driven. We find
that this produces a form of compositionally-tuned, insulating, ferrimagnetic
quantum criticality. Close to the zero temperature phase transition we observe
the emergence of an electric-dipole glass induced by magneto-electric coupling.
The strong frequency behaviour of the glass freezing temperature $T_m$ has a
Vogel-Fulcher dependence with $T_m$ finite, or suppressed below zero in the
zero frequency limit, depending on composition $x$. These quantum-mechanical
properties, along with the multiplicity of low-lying modes near to the
zero-temperature phase transition, are likely to greatly extend applications of
hexaferrites into the realm of quantum and cryogenic technologies.",1708.03945v1
2018-04-06,Effect of Substrate Temperature on Structural and Magnetic Properties of c-axis Ori-ented Spinel Ferrite Ni0.65Zn0.35Fe2O4 (NZFO) Thin Films,"Varying the substrate temperature changes structural and magnetic properties
of spinel ferrite NZFO thin films. XRD of films grown at different temperature
display only 004 reflections, without any secondary peaks, showing growth
orientation along the c axis. We find an increase in crystalline quality of
these thin films with the rise of substrate temperature. The surface topography
of the thin films grown on various growth temperatures conditions reveal that
these films are smooth with low roughness, however the thin films grown at 800
C exhibit lowest average and rms roughness among all thin films. We find iron
and nickel to be more oxidized i,e greater Fe and Ni content in films grown and
annealed at 700 C and 800 C, compared to those grown at lower temperatures. The
magnetic moment is observed to increase with an increase of substrate
temperature and all thin films possess high saturation magnetization and low
coercive field at room temperature. Films grown at 800 C exhibit a
ferrimagnetic paramagnetic phase transition well above room temperature. The
observed large magnetizations with soft magnetic behavior in NZFO thin films
above room temperature suggest potential application in memory, spintronics,
and multifunctional devices.",1804.02458v2
2018-04-20,From Charge to Orbital Ordered Metal-Insulator Transition in Alkaline-Earth Ferrites,"While CaFeO$_3$ exhibits upon cooling a metal-insulator transition linked to
charge ordering, SrFeO$_3$ and BaFeO$_3$ keep metallic behaviors down to very
low temperatures. Moreover, alkaline-earth ferrites do not seem prone to
orbital ordering in spite of the d$^4$ formal occupancy of Fe$^{4+}$. Here,
from first-principles simulations, we show that the metal-insulator transition
of CaFeO$_3$ is structurally triggered by oxygen rotation motions as in
rare-earth nickelates. This not only further clarifies why SrFeO$_3$ and
BaFeO$_3$ remain metallic but allows us to predict that an insulating
charge-ordered phase can be induced in SrFeO$_3$ from appropriate engineering
of oxygen rotation motions. Going further, we unveil the possibility to switch
from the usual charge-ordered to an orbital-ordered insulating ground state
under moderate tensile strain in CaFeO$_3$ thin films. We rationalize the
competition between charge and orbital orderings, highlighting alternative
possible strategies to produce such a change of ground state, also relevant to
manganite and nickelate compounds.",1804.07584v2
2020-07-29,All-optical nonreciprocity due to valley polarization in transition metal dichalcogenides,"Nonreciprocity and nonreciprocal optical devices play a vital role in modern
photonic technologies by enforcing one-way propagation of light. Most
nonreciprocal devices today are made from a special class of low-loss ferrites
that exhibit a magneto-optical response in the presence of an external static
magnetic field. While breaking transmission symmetry, ferrites fail to satisfy
the need for miniaturization of photonic circuitry due to weak character of
nonreciprocal responses at optical wavelengths and are not easy to integrate
into on-chip photonic systems. These challenges led to the emergence of
magnetic-free approaches relying on breaking time reversal symmetry, e.g. with
nonlinear effects modulating optical system in time. Here, we demonstrate an
all-optical approach to nonreciprocity based on nonlinear valley-selective
response in transition metal dichalcogenides (TMDs). This approach overcomes
the limitations of magnetic materials and it does not require an external
magnetic field. We provide experimental evidence of photoinduced nonreciprocity
in a monolayer WS2 pumped by circularly polarized light. Nonreciprocity stems
from valley-selective exciton-exciton interactions, giving rise to nonlinear
circular dichroism controlled by circularly polarized pump fields. Our
experimental results reveal a significant effect even at room temperature,
despite considerable intervalley-scattering, showing potential for practical
applications in magnetic-free nonreciprocal platforms. As an example, we
propose a device scheme to realize an optical isolator based on a pass-through
silicon nitride (SiN) ring resonator integrating the optically biased TMD
monolayer.",2007.14934v1
2017-01-23,Size Effects of Ferroelectric and Magnetoelectric Properties of Semi-ellipsoidal Bismuth Ferrite Nanoparticles,"Bismuth ferrite (BiFeO3) is one of the most promising multiferroics with a
sufficiently high ferroelectric (FE) and antiferromagnetic transition
temperatures, and magnetoelectric (ME) coupling coefficient at room
temperature, and thus it is highly sensitive to the impact of cross-influence
of applied electric and magnetic fields. According to the urgent demands of
nanotechnology miniaturization for ultra-high density data storage in advanced
nonvolatile memory cells, it is very important to reduce the sizes of
multiferroic nanoparticles in the self-assembled arrays without serious
deterioration of their properties. We study size effects of the phase diagrams,
FE and ME properties of semi-ellipsoidal BiFeO3 nanoparticles clamped to a
rigid conductive substrate. The spatial distribution of the spontaneous
polarization vector inside the nanoparticles, phase diagrams and
paramagnetoelectric (PME) coefficient were calculated in the framework of
modified Landau-Ginzburg-Devonshire (LGD) approach. Analytical expressions were
derived for the dependences of the FE transition temperature, average
polarization, linear dielectric susceptibility and PME coefficient on the
particle sizes for a general case of a semi-ellipsoidal nanoparticles with
three different semi-axes a, b and height c. The analyses of the obtained
results leads to the conclusion that the size effect of the phase diagrams,
spontaneous polarization and PME coefficient is rather sensitive to the
particle sizes aspect ratio in the polarization direction, and less sensitive
to the absolute values of the sizes per se.",1701.06468v1
2017-04-14,Thermostat Influence on the Structural Development and Material Removal during Abrasion of Nanocrystalline Ferrite,"We consider a nanomachining process of hard, abrasive particles grinding on
the rough surface of a polycrystalline ferritic work piece. Using extensive
large-scale molecular dynamics (MD) simulations, we show that the mode of
thermostatting, i.e., the way that the heat generated through deformation and
friction is removed from the system, has crucial impact on tribological and
materials related phenomena. By adopting an electron-phonon coupling approach
to parametrize the thermostat of the system, thus including the electronic
contribution to the thermal conductivity of iron, we can reproduce the
experimentally measured values that yield realistic temperature gradients in
the work piece. We compare these results to those obtained by assuming the two
extreme cases of only phononic heat conduction and instantaneous removal of the
heat generated in the machining interface. Our discussion of the differences
between these three cases reveals that although the average shear stress is
virtually temperature independent up to a normal pressure of approximately 1
GPa, the grain and chip morphology as well as most relevant quantities depend
heavily on the mode of thermostatting beyond a normal pressure of 0.4 GPa.
These pronounced differences can be explained by the thermally activated
processes that guide the reaction of the Fe lattice to the external mechanical
and thermal loads caused by nanomachining.",1704.04384v1
2008-07-27,Do the Tellegen particles really exist in electromagnetics?,"In 1948 Tellegen suggested that an assembly of the lined up electric-magnetic
dipole twins can construct a new type of an electromagnetic material. Till now,
however, the problem of creation of the Tellegen medium is a subject of strong
discussions. An elementary symmetry analysis makes questionable an idea of a
simple combination of two (electric and magnetic) dipoles to realize local
materials with the Tellegen particles as structural elements. In this paper we
show that in his search of sources with local junctions of the electrical and
magnetic properties one cannot rely on the induced parameters of small
electromagnetic scatterers. No near-field electromagnetic structures and
classical motion equations for point charges give a physical basis to realize
sources with the local junction of the electrical and magnetic properties. We
advance a hypothesis that local magnetoelectric (ME) particles should be the
physical objects with eigenmode oscillation spectra and non-classical symmetry
breaking effects. Our studies convincingly prove this assumption. We show that
a quasi-2D ferrite disk with magnetic-dipolar-mode oscillations is
characterized by unique symmetry features with topological phases resulting in
appearance of the ME properties. The entire ferrite disk can be characterized
as a combined system with eigen electric and magnetic moments. The fields near
such a particle are distinguished by special symmetry properties.",0807.4280v1
2011-11-18,Microwave magnetoelectric fields,"We show that in a source-free subwavelength region of microwave fields there
can exist the field structures with local coupling between the time-varying
electric and magnetic fields differing from the electric-magnetic coupling in
regular-propagating free-space electromagnetic waves. To distinguish such field
structures from regular electromagnetic (EM) field structures, we term them as
magnetoelectric (ME) fields. We study a structure and conservation laws of
microwave ME near fields. We show that there exist sources of microwave ME near
fields - the ME particles. These particles are represented by small quasi-2D
ferrite disks with the magnetic-dipolar-oscillation spectra. The near fields
originated from such particles are characterized by topologically distinctive
power-flow vortices, non-zero helicity, and a torsion degree of freedom. Our
studies of the microwave ME near fields are combined in two successive papers.
In this paper we give a theoretical background of properties of the electric
and magnetic fields inside and outside of a ferrite particle with
magnetic-dipolar-oscillation spectra resulting in appearance of the microwave
ME near fields. Based on the obtained structures of the ME near fields, we
discuss effects of so-called ME interactions observed in artificial
electromagnetic materials. In the next paper, we represent numerical and
experimental studies of the microwave ME near fields and their interactions
with matter.",1111.4359v1
2016-12-24,Nonreciprocal reconfigurable microwave optomechanical circuit,"Devices that achieve nonreciprocal microwave transmission are ubiquitous in
radar and radio-frequency communication systems, and commonly rely on
magnetically biased ferrite materials. Such devices are also indispensable in
the readout chains of superconducting quantum circuits as they protect
sensitive quantum systems from the noise emitted by readout electronics. Since
ferrite-based nonreciprocal devices are bulky, lossy, and require large
magnetic fields, there has been significant interest in magnetic-field-free
on-chip alternatives, such as those recently implemented using Josephson
junctions. Here we realise reconfigurable nonreciprocal transmission between
two microwave modes using purely optomechanical interactions in a
superconducting electromechanical circuit. We analyse the transmission as well
as the noise properties of this nonreciprocal circuit. The scheme relies on the
interference in two mechanical modes that mediate coupling between microwave
cavities. Finally, we show how quantum-limited circulators can be realized with
the same principle. The technology can be built on-chip without any external
magnetic field, and is hence fully compatible with superconducting quantum
circuits. All-optomechanically-mediated nonreciprocity demonstrated here can
also be extended to implement directional amplifiers, and it forms the basis
towards realising topological states of light and sound.",1612.08223v3
2017-12-15,"Tunable polymorphism of epitaxial iron oxides in the four-in-one ferroic-on-GaN system with magnetically ordered α-, γ-, ε-Fe2O3 and Fe3O4 layers","Hybridization of semiconducting and magnetic materials into a single
heterostructure is believed to be potentially applicable to the design of novel
functional spintronic devices. In the present work we report epitaxial
stabilization of four magnetically ordered iron oxide phases (Fe3O4,
{\gamma}-Fe2O3, {\alpha}-Fe2O3 and most exotic metastable {\epsilon}-Fe2O3) in
the form of nanometer sized single crystalline films on GaN(0001) surface. The
epitaxial growth of as many as four distinctly different iron oxide phases is
demonstrated within the same single-target Laser MBE technological process on a
GaN semiconductor substrate widely used for electronic device fabrication. The
discussed iron oxides belong to a family of simple formula magnetic materials
exhibiting a rich variety of outstanding physical properties including peculiar
Verwey and Morin phase transitions in Fe3O4 and {\alpha}-Fe2O3 and multiferroic
behavior in metastable magnetically hard {\epsilon}-Fe2O3 ferrite. The physical
reasons standing behind the nucleation of a particular phase in an epitaxial
growth process deserve interest from the fundamental point of view. The
practical side of the presented study is to exploit the tunable polymorphism of
iron oxides for creation of ferroic-on-semiconductor heterostructures usable in
novel spintronic devices. By application of a wide range of experimental
techniques the surface morphology, crystalline structure, electronic and
magnetic properties of the single phase iron oxide epitaxial films on GaN have
been studied. A comprehensive comparison has been made to the properties of the
same ferrite materials in the bulk and nanostructured form reported by other
research groups.",1712.05632v1
2017-12-17,"Low temperature ferromagnetic properties, magnetic field induced spin order and random spin freezing effect in Ni1.5Fe1.5O4 ferrite; prepared at different pH values and annealing temperatures","We present the low temperature magnetic properties in Ni1.5Fe1.5O4 ferrite as
the function of pH at which the material was prepared by chemical route and
post annealing temperature. The material is a ferri or ferromagnet, but showed
magnetic blocking and random spin freezing process on lowering the measurement
temperature down to 5 K. The sample prepared at pH =12 and annealed at 800 ^C
showed a sharp magnetization peak at 105 K, the superparamagnetic blocking
temperature of the particles. The magnetization peak remained incomplete within
measurement temperature up to 350 K for rest of the samples, although peak
temperature was brought down by increasing applied dc field. The fitting of
temperature dependence of coercivity data according to Kneller law suggested
random orientation of ferromagnetic particles. The fitting of saturation
magnetization according to Bloch law provided the exponent that largely
deviated from 1.5, a typical value for long ranged ferromagnet. An abrupt
increase of saturation magnetization below 50 K suggested the active role of
frozen surface spins in low temperature magnetic properties. AC susceptibility
data elucidated the low temperature spin freezing dynamics and exhibited the
characters of cluster spin glass in the samples depending on pH value and
annealing temperature.",1712.06114v1
2019-10-24,"Solute diffusion by self-interstitial defects and radiation-induced segregation in ferritic Fe-X (X=Cr, Cu, Mn, Ni, P, Si) dilute alloys","This work investigates solute transport due to self-interstitial defects and
radiation induced segregation tendencies in dilute ferritic alloys, by
computing the transport coefficients of each system based on ab initio
calculations of binding energies and migration rates. The implementation of the
self-consistent mean field method in the KineCluE code allows to extend the
calculation of transport coefficients to arbitrary interaction ranges, crystal
structures, and diffusion mechanisms. The results show that the diffusivity of
P, Mn, and Cr solute atoms is dominated by the dumbbell mechanism, that of Cu
by vacancies, while the two mechanisms might be in competition for Ni and Si,
despite the fact that the corresponding mixed dumbbells are not stable.
Systematic enrichment at defect sinks is expected for P and Mn solutes due to
dumbbell diffusion, and for Si due mainly to vacancy drag. Vacancy drag is also
responsible for Cu and Ni enrichment below 1085 K. The RIS behavior of Cr is
the outcome of a fine balance between dumbbell enrichment and vacancy
depletion. Therefore, for dilute Cr concentrations global enrichment occurs
below 540 K, and depletion above. This threshold temperature grows with solute
concentration. The findings are in agreement with experimental observations of
RIS and clustering phenomena, and confirm that solute-defect kinetic coupling
plays an important role in the formation of solute clusters in reactor pressure
vessel steels and other alloys.",1910.11440v2
2021-01-13,An empirical approach to measuring interface energies in mixed-phase bismuth ferrite,"In complex oxide heteroepitaxy, strain engineering is a powerful tool to
obtain phases in thin films that may be otherwise unstable in bulk. A
successful example of this approach is mixed phase bismuth ferrite (BiFeO3)
epitaxial thin films. The coexistence of a tetragonal-like (T-like) matrix and
rhombohedral-like (R-like) striations provides an enhanced electromechanical
response, along with other attractive functional behaviors. In this paper, we
compare the energetics associated with two thickness dependent strain
relaxation mechanisms in this system: domain walls arising from monoclinic
distortion in the T-like phase, and the interphase boundary between the host
T-like matrix and tilted R-like phases. Combining x-ray diffraction
measurements with scanning probe microscopy, we extract quantitative values
using an empirical energy balance approach. The domain wall and phase boundary
energies are found to be 113 $\pm$ 21 and 426 $\pm$ 23 mJ.m$^{-2}$,
respectively. These numerical estimates will help us realize designer phase
boundaries in multiferroics, which possess colossal responses to external
stimuli, attractive for a diverse range of functional applications.",2101.04883v2
2017-11-27,Cavity Magnon Polaritons with Lithium Ferrite and 3D Microwave Resonators at milli-Kelvin Temperatures,"Single crystal Lithium Ferrite (LiFe) spheres of sub-mm dimension are
examined at mK temperatures, microwave frequencies and variable DC magnetic
field, for use in hybrid quantum systems and condensed matter and fundamental
physics experiments. Strong coupling regimes of the photon-magnon interaction
(cavity magnon polariton quasi-particles) were observed with coupling strength
of up to 250 MHz at 9.5 GHz (2.6\%) with magnon linewidths of order 4 MHz (with
potential improvement to sub-MHz values). We show that the photon-magnon
coupling can be significantly improved and exceed that of the widely used
Yttrium Iron Garnet crystal, due to the small unit cell of LiFe, allowing twice
more spins per unit volume. Magnon mode softening was observed at low DC fields
and combined with the normal Zeeman effect creates magnon spin wave modes that
are insensitive to first order order magnetic field fluctuations. This effect
is observed in the Kittel mode at 5.5 GHz (and another higher order mode at 6.5
GHz) with a DC magnetic field close to 0.19 Tesla. We show that if the cavity
is tuned close to this frequency, the magnon polariton particles exhibit an
enhanced range of strong coupling and insensitivity to magnetic field
fluctuations with both first order and second order insensitivity to magnetic
field as a function of frequency (double magic point clock transition), which
could potentially be exploited in cavity QED experiments.",1711.09980v2
2019-02-19,"Elemental substitution tuned magneto elastoviscous behavior of nanoscale ferrite MFe2O4 M = Mn, Fe, Co, Ni based complex fluids","The present article reports the governing influence of substituting the M2
site in nanoscale MFe2O4 spinel ferrites by different magnetic metals
Fe,Mn,Co,Ni on magnetorheological and magneto elastoviscous behaviors of the
corresponding magnetorheological fluids MRFs. Different doped MFe2O4
nanoparticles have been synthesized using the polyol assisted hydrothermal
method. Detailed steady and oscillatory shear rheology have been performed on
the MRFs to determine the magneto-viscoelastic responses. The MRFs exhibit
shear thinning behavior and augmented yield characteristics under influence of
magnetic field. The steady state magnetoviscous behaviors are scaled against
the governing Mason number and self similar response from all the MRFs have
been noted. The MRFs conform to an extended Bingham plastic model under field
effect. Transient magnetoviscous responses show distinct hysteresis behaviors
when the MRFs are exposed to time varying magnetic fields. Oscillatory shear
studies using frequency and strain amplitude sweeps exhibit predominant solid
like behaviors under field environment. However, the relaxation behaviors and
strain amplitude sweep tests of the MRFs reveal that while the fluids show
solid like behaviors under field effect, they cannot be termed as typical
elastic fluids. Comparisons show that the MnFe2O4 MRFs have superior yield
performance among all. However, in case of dynamic and oscillatory systems,
CoFe2O4 MRFs show the best performance. The viscoelastic responses of the MRFs
are noted to correspond to a three element viscoelastic model. The study may
find importance in design and development strategies of nano MRFs for different
applications.",1902.09315v1
2019-04-02,Magnetoelectrically driven catalytic degradation of organics,"Here, we report the catalytic degradation of organic compounds by exploiting
the magnetoelectric (ME) nature of cobalt ferrite-bismuth ferrite (CFO-BFO)
core-shell nanoparticles. The combination of magnetostrictive CFO with the
multiferroic BFO gives rise to a magnetoelectric engine that purifies water
under wireless magnetic fields via advanced oxidation processes, without
involvement of any sacrificial molecules or co-catalysts. Magnetostrictive
CoFe2O4 nanoparticles are fabricated using hydrothermal synthesis, followed by
sol-gel synthesis to create the multiferroic BiFeO3 shell. We perform
theoretical modeling to study the magnetic field induced polarization on the
surface of magnetoelectric nanoparticles. The results obtained from these
simulations are consistent with the experimental findings of the piezo-force
microscopy analysis, where we observe changes in the piezoresponse of the
nanoparticles under magnetic fields. Next, we investigate the magnetoelectric
effect induced catalytic degradation of organic pollutants under AC magnetic
fields and obtained 97% removal efficiency for synthetic dyes and over 85%
removal efficiency for routinely used pharmaceuticals. Additionally, we perform
trapping experiments to elucidate the mechanism behind the magnetic field
induced catalytic degradation of organic pollutants by using scavengers for
each of the reactive species. Our results indicate that hydroxyl and superoxide
radicals are the main reactive species in the magnetoelectrically induced
catalytic degradation of organic compounds.",1904.01271v1
2019-08-22,Influence of structure and cation distribution on magnetic anisotropy and damping in Zn/Al doped nickel ferrites,"An in-depth analysis of Zn/Al doped nickel ferrites grown by reactive
magnetron sputtering is relevant due to their promising characteristics for
applications in spintronics. The material is insulating and ferromagnetic at
room temperature with an additional low magnetic damping. By studying the
complex interplay between strain and cation distribution their impact on the
magnetic properties, i.e. anisotropy, damping and g-factor is unravelled. In
particular, a strong influence of the lattice site occupation of
Ni$^{2+}_{\text{Td}}$ and cation coordination of Fe$^{2+}_{\text{Oh}}$ on the
intrinsic damping is found. Furthermore, the critical role of the incorporation
of Zn$^{2+}$ and Al$^{3+}$ is evidenced by comparison with a sample of altered
composition. Especially, the dopant Zn$^{2+}$ is evidenced as a tuning factor
for Ni$^{2+}_{\text{Td}}$ and therefore unquenched orbital moments directly
controlling the g-factor. A strain-independent reduction of the magnetic
anisotropy and damping by adapting the cation distribution is demonstrated.",1908.08257v3
2019-11-12,Diamond magnetometer enhanced by ferrite flux concentrators,"Magnetometers based on nitrogen-vacancy (NV) centers in diamond are promising
room-temperature, solid-state sensors. However, their reported sensitivity to
magnetic fields at low frequencies (<1 kHz) is presently >10 pT s^{1/2},
precluding potential applications in medical imaging, geoscience, and
navigation. Here we show that high-permeability magnetic flux concentrators,
which collect magnetic flux from a larger area and concentrate it into the
diamond sensor, can be used to improve the sensitivity of diamond
magnetometers. By inserting an NV-doped diamond membrane between two ferrite
cones in a bowtie configuration, we realize a ~250-fold increase of the
magnetic field amplitude within the diamond. We demonstrate a sensitivity of
~0.9 pT s^{1/2} to magnetic fields in the frequency range between 10 and 1000
Hz, using a dual-resonance modulation technique to suppress the effect of
thermal shifts of the NV spin levels. This is accomplished using 200 mW of
laser power and 20 mW of microwave power. This work introduces a new dimension
for diamond quantum sensors by using micro-structured magnetic materials to
manipulate magnetic fields.",1911.05070v2
2020-05-26,Nonlinear Spin Currents,"The cavity mediated spin current between two ferrite samples has been
reported by Bai et. al. [Phys. Rev. Lett. 118, 217201 (2017)]. This experiment
was done in the linear regime of the interaction in the presence of external
drive. In the current paper we develop a theory for the spin current in the
nonlinear domain where the external drive is strong so that one needs to
include the Kerr nonlinearity of the ferrite materials. In this manner the
nonlinear polaritons are created and one can reach both bistable and
multistable behavior of the spin current. The system is driven into a far from
equilibrium steady state which is determined by the details of driving field
and various interactions. We present a variety of steady state results for the
spin current. A spectroscopic detection of the nonlinear spin current is
developed, revealing the key properties of the nonlinear polaritons. The
transmission of a weak probe is used to obtain quantitative information on the
multistable behavior of the spin current. The results and methods that we
present are quite generic and can be used in many other contexts where cavities
are used to transfer information from one system to another, e.g., two
different molecular systems.",2005.12999v1
2020-08-03,Solute hydrogen and deuterium observed at the near atomic scale in high-strength steel,"Observing solute hydrogen (H) in matter is a formidable challenge, yet,
enabling quantitative imaging of H at the atomic-scale is critical to
understand its deleterious influence on the mechanical strength of many
metallic alloys that has resulted in many catastrophic failures of engineering
parts and structures. Here, we report on the APT analysis of hydrogen (H) and
deuterium (D) within the nanostructure of an ultra-high strength steel with
high resistance to hydrogen embrittlement. Cold drawn, severely deformed
pearlitic steel wires (Fe-0.98C-0.31Mn-0.20Si-0.20Cr-0.01Cu-0.006P-0.007S wt.%,
{\epsilon}=3.1) contains cementite decomposed during the pre-deformation of the
alloy and ferrite. We find H and D within the decomposed cementite, and at some
interfaces with the surrounding ferrite. To ascertain the origin of the H/D
signal obtained in APT, we explored a series of experimental workflows
including cryogenic specimen preparation and cryogenic-vacuum transfer from the
preparation into a state-of-the-art atom probe. Our study points to the
critical role of the preparation, i.e. the possible saturation of H-trapping
sites during electrochemical polishing, how these can be alleviated by the use
of an outgassing treatment, cryogenic preparation and transfer prior to
charging. Accommodation of large amounts of H in the under-stoichiometric
carbide likely explains the resistance of pearlite against hydrogen
embrittlement.",2008.00684v1
2020-11-25,Nanoscale ferroelectricity in pseudo-cubic sol-gel derived barium titanate -- bismuth ferrite (BaTiO$_3$-BiFeO$_3$) solid solutions,"Single phase barium titanate-bismuth ferrite ((1-x)BaTi$_3$-(x)BiFe$_3$,
BTO-BFO) solid solutions were prepared using citric acid and ethylene glycol
assisted sol-gel synthesis method. Depending on the dopant content the samples
are characterized by tetragonal, tetragonal-pseudocubic, pseudocubic and
rhombohedral structure as confirmed by Raman spectroscopy and XRD measurements.
An increase of the BFO content leads to a reduction in the cell parameters
accompanied by a decrease in polar distortion of the unit cell wherein an
average particle size increases from 60 up to 350 nm. Non zero piezoresponse
was observed in the compounds with pseudocubic structure while no polar
distortion was detected in their crystal structure using X-ray diffraction
method. The origin of the observed non-negligible piezoresponse was discussed
assuming a coexistence of nanoscale polar and non-polar phases attributed to
the solid solutions with high BFO content. A coexistence of the nanoscale
regions having polar and non-polar character is considered as a key factor to
increase macroscopic piezoresponse in the related compounds due to increased
mobility of the domain walls and phase boundaries.",2011.12721v1
2021-02-16,Layer and spontaneous polarizations in perovskite oxides and their interplay in multiferroic bismuth ferrite,"We review the concept of surface charge, first in the context of the
polarization in ferroelectric materials, and second in the context of layers of
charged ions in ionic insulators. While the former is traditionally discussed
in the ferroelectrics community, and the latter in the surface science
community, we remind the reader that the two descriptions are conveniently
unified within the modern theory of polarization. In both cases, the surface
charge leads to electrostatic instability - the so-called ""polar catastrophe"" -
if it is not compensated, and we review the range of phenomena that arise as a
result of different compensation mechanisms. We illustrate these concepts using
the example of the prototypical multiferroic bismuth ferrite, BiFeO3, which is
unusual in that its spontaneous ferroelectric polarization and its layer
charges can be of the same magnitude. As a result, for certain combinations of
polarization orientation and surface terminationits surface charge is
self-compensating. We use density functional calculations of BiFeO3 slabs and
superlattices, analysis of high-resolution transmission electron micrographs as
well as examples from the literature to explore the consequences of this
peculiarity.",2102.08082v2
2021-02-18,Modelling the relationship between deformed microstructures and static recrystallization textures: application to ferritic stainless steels,"We present an original approach for predicting the static recrystallization
texture development during annealing of deformed crystalline materials. The
microstructure is considered as a population of subgrains and grains whose
sizes and boundary properties determine their growth rates. The model input
parameters are measured directly on orientation maps maps of the deformed
microstructure measured by electron backscattered diffraction. The anisotropy
in subgrain properties then drives a competitive growth giving rise to the
recrystallization texture development. The method is illustrated by a
simulation of the static recrystallization texture development in a hot rolled
ferritic stainless steel. The model predictions are found to be in good
agreement with the experimental measurements, and allow for an in-depth
investigation of the formation sequence of the recrystallization texture. A
distinction is established between the texture components which develop due to
favorable growth conditions and those developing due to their predominance in
the prior deformed state. The high fraction of alpha fibre orientations in the
recrystallized state is shown to be a consequence of their predominance in the
deformed microstructure rather than a preferred growth mechanism. A close
control of the fraction of these orientations before annealing is thus required
to minimize their presence in the recrystallized state.",2102.09597v1
2021-06-03,Macrospin model of an assembly of magnetically coupled core-shell nanoparticles,"Highly sophisticated synthesis methods and experimental techniques allow for
precise measurements of magnetic properties of nanoparticles that can be
reliably reproduced using theoretical models. Here, we investigate the magnetic
properties of ferrite nanoparticles by using theoretical techniques based on
Monte Carlo methods. We introduce three stages of sophistication in the
macromagnetic model. First, by using tailor-made hamiltonians we study single
nanoparticles. In a second stage, the internal structure of the nanoparticle is
taken into consideration by defining an internal (core) and external (shell)
region, respectively. In the last stage, an assembly of core/shell NPs are
considered. All internal magnetic couplings such as inter and intra-atomic
exchange interactions or magnetocrystalline anisotropies have been estimated.
Moreover, the hysteresis loops of the aforementioned three cases have been
calculated and compared with recent experimental measurements. In the case of
the assembly of nanoparticles, the hysteresis loops together with the
zero-field cooling and field cooling curves are shown to be in a very good
agreement with the experimental data. The current model provides an important
tool to understand the internal structure of the nanoparticles together with
the complex internal spin interactions of the core-shell ferrite nanoparticles.",2106.01844v1
2022-09-19,Resolving diverse oxygen transport pathways across Sr-doped lanthanum ferrite and metal-perovskite heterostructures,"Perovskite structured transition metal oxides are important technological
materials for catalysis and solid oxide fuel cell applications. Their
functionality often depends on oxygen diffusivity and mobility through complex
oxide heterostructures, which can be significantly impacted by structural and
chemical modifications, such as doping. Further, when utilized within
electrochemical cells, interfacial reactions with other components (e.g. Ni-
and Cr-based alloy electrodes and interconnects) can influence the perovskite's
reactivity and ion transport, leading to complex dependencies that are
difficult to control in real-world environments. Here we use isotopic tracers
and atom probe tomography to directly visualize oxygen diffusion and transport
pathways across perovskite and metal-perovskite heterostructures, i.e. (Ni-Cr
coated) Sr-doped lanthanum ferrite (LSFO). Annealing in 18O2(g) results in
elemental and isotopic redistributions through oxygen exchange (OE) in the LSFO
while Ni-Cr undergoes oxidation via multiple mechanisms and transport pathways.
Complementary density functional theory (DFT) calculations at experimental
conditions provide rationale for OE reaction mechanisms and reveal a complex
interplay of different thermodynamic and kinetic drivers. Our results shed
light on the fundamental coupling of defects and oxygen transport in an
important class of catalytic materials.",2209.09302v1
2023-01-25,Room-temperature spin glass behavior in zinc ferrite epitaxial thin films,"Zinc ferrite (ZnFe$_{\text{2}}$O$_{\text{4}}$) epitaxial thin films were
grown by reactive magnetron sputtering on MgAl$_{\text{2}}$O$_{\text{4}}$ and
Al$_{\text{2}}$O$_{\text{3}}$ substrates varying a range of preparation
parameters. The resulting structural and magnetic properties were investigated
using a range of experimental techniques confirming epitaxial growth of
ZnFe$_{\text{2}}$O$_{\text{4}}$ with the nominal stoichiometric composition and
long range magnetic order at and above room temperature. The main preparation
parameter influencing the temperature $T_{\text{f}}$ of the bifurcation between
$M(T)$ curves under field cooled and zero-field cooled conditions was found to
be the growth rate of the films, while growth temperature or the Ar:O$_2$ ratio
did not systematically influence $T_{\text{f}}$. Furthermore $T_{\text{f}}$ was
found to be systematically higher for MgAl$_{\text{2}}$O$_{\text{4}}$ as
substrate and $T_{\text{f}}$ extends to above room temperature. While in some
samples $T_{\text{f}}$ seems to be more likely correlated with
superparamagentism, the highest $T_{\text{f}}$ occurs in
ZnFe$_{\text{2}}$O$_{\text{4}}$ epitaxial films where experimental signatures
of magnetic glassiness can be found. Element-selective X-ray magnetic circular
dichroism measurements aim at associating the magnetic glassiness with the
occurrence of a different valence state and lattice site incorporation of Fe
pointing to a complex interplay of various competing magnetic interactions in
ZnFe$_{\text{2}}$O$_{\text{4}}$.",2301.11277v1
2023-02-10,Laser-induced magnonic band gap formation and control in YIG/GaAs heterostructure,"We demonstrate the laser-induced control over spin-wave (SW) transport in the
magnonic crystal (MC) waveguide formed from the semiconductor slab placed on
the ferrite film. We considered bilayer MC with periodical grooves performed on
the top of the n-type gallium arsenide slab side that oriented to the yttrium
iron garnet film. To observe the appearance of magnonic gap induced by laser
radiation, the fabricated structure was studied by the use of microwave
spectroscopy and Brillouin light-scattering. We perform detailed numerical
studies of this structure. We showed that the optical control of the magnonic
gaps (frequency width and position) is related to the variation of the charge
carriers' concentration in GaAs. We attribute these to nonreciprocity of SW
transport in the layered structure. Nonreciprocity was induced by the laser
exposure of the GaAs slab due to SWs' induced electromagnetic field screening
by the optically-generated charge carriers. We showed that SW dispersion,
nonreciprocity, and magnonic band gap position and width in the
ferrite-semiconductor magnonic crystal can be modified in a controlled manner
by laser radiation. Our results show the possibility of the integration of
magnonics and semiconductor electronics on the base of YIG/GaAs structures.",2302.05310v1
2023-08-15,Microstructural and material property changes in severely deformed Eurofer-97,"Severe plastic deformation changes the microstructure and properties of
steels, which may be favourable for their use in structural components of
nuclear reactors. In this study, high-pressure torsion (HPT) was used to refine
the grain structure of Eurofer-97, a ferritic/ martensitic steel. Electron
microscopy and X-ray diffraction were used to characterise the microstructural
changes. Following HPT, the average grain size reduced by a factor of $\sim$
30, with a marked increase in high-angle grain boundaries. Dislocation density
also increased by more than one order of magnitude. The thermal stability of
the deformed material was investigated via in-situ annealing during synchrotron
X-ray diffraction. This revealed substantial recovery between 450 K - 800 K.
Irradiation with 20 MeV Fe-ions to $\sim$ 0.1 dpa caused a 20% reduction in
dislocation density compared to the as-deformed material. However, HPT
deformation prior to irradiation did not have a significant effect in
mitigating the irradiation-induced reductions in thermal diffusivity and
surface acoustic wave velocity of the material. These results provide a
multi-faceted understanding of the changes in ferritic/martensitic steels due
to severe plastic deformation, and how these changes can be used to alter
material properties.",2308.07735v1
2023-09-24,Hexaferrite-based permanent magnets with upper magnetic properties by cold sintering process via a non-aqueous solvent,"The incessant technological pursuit towards a more sustainable and green
future depends strongly on permanent magnets. At present, their use is
widespread, making it imperative to develop new processing methods that
generate highly competitive magnetic properties reducing the fabrication
temperatures and costs. Herein, a novel strategy for developing dense sintered
magnets based on Sr-hexaferrites with upper functional characteristics is
presented. An innovative cold sintering approach using glacial acetic acid as
novelty, followed by a post-annealing at 1100 {\deg}C, achieves a densification
of the ceramic magnets of 92% with respect to the theoretical density and
allows controlling the particle growth. After the cold sintering process, a
fraction of amorphous SrO is identified, in addition to a partial
transformation to {\alpha}-Fe2O3 as secondary crystalline phase. 46 wt% of
SrFe12O19 remains, which is mostly recuperated after the post-thermal
treatment. These findings do not significantly modify the final structure of
ferrite magnets, neither at short- nor long-range order. The innovative process
has a positive impact on the magnetic properties, yielding competitive ferrite
magnets at lower sintering temperatures with an energy efficiency of at least
25%, which opens up a new horizon in the field of rare-earth free permanent
magnets and new possibilities in other applications.",2309.13719v1
2023-09-26,Duality of switching mechanisms and transient negative capacitance in improper ferroelectrics,"The recent discovery of transient negative capacitance has sparked an intense
debate on the role of homogeneous and inhomogeneous mechanisms in polarizations
switching. In this work, we report observation of transient negative
capacitance in improper ferroelectric h-YbFeO3 films in a resistor-capacitor
circuit, and a concaved shape of anomaly in the voltage wave form, in the early
and late stage of the polarizations switching respectively. Using a
phenomenological model, we show that the early-stage negative capacitance is
likely due to the inhomogeneous switching involving nucleation and domain wall
motion, while the anomaly at the late stage, which appears to be a reminiscent
negative capacitance is the manifestation of the thermodynamically unstable
part of the free-energy landscape in the homogeneous switching. The complex
free-energy landscape in hexagonal ferrites may be the key to cause the abrupt
change in polarization switching speed and the corresponding anomaly. These
results reconcile the two seemingly conflicting mechanisms in the polarization
switching and highlight their different roles at different stages. The unique
energy-landscape in hexagonal ferrites that reveals the dual switching
mechanism suggests the promising application potential in terms of negative
capacitance.",2309.14639v1
2024-01-26,Reactive additive capillary stamping with double network hydrogel-derived aerogel stamps under solvothermal conditions,"Integration of solvothermal reaction products into complex thin-layer
architectures is frequently achieved by combinations of layer transfer and
subtractive lithography, whereas direct additive substrate patterning with
solvothermal reaction products has remained challenging. We report reactive
additive capillary stamping under solvothermal conditions as a parallel
contact-lithographic access to patterns of solvothermal reaction products in
thin-layer configurations. To this end, corresponding precursor inks are
infiltrated into mechanically robust mesoporous aerogel stamps derived from
double-network hydrogels (DNHGs). The stamp is then brought into contact with a
substrate to be patterned under solvothermal reaction conditions inside an
autoclave. The precursor ink forms liquid bridges between the topographic
surface pattern of the stamp and the substrate. Evaporation-driven enrichment
of the precursors in these liquid bridges along with their liquid-bridge-guided
conversion into the solvothermal reaction products yields large-area submicron
patterns of the solvothermal reaction products replicating the stamp
topography. As example, we prepared thin hybrid films, which contained ordered
monolayers of superparamagnetic submicron nickel ferrite dots prepared by
solvothermal capillary stamping surrounded by nickel electrodeposited in a
second, orthogonal substrate functionalization step. The submicron nickel
ferrite dots acted as magnetic hardener halving the remanence of the
ferromagnetic nickel layer. In this way, thin-layer electromechanical systems,
transformers and positioning systems may be customized.",2401.15013v1
2024-02-25,High-resolution numerical-experimental comparison of heterogeneous slip activity in quasi-2D ferrite sheets,"The role of heterogeneity in the plastic flow of thin ferrite specimens is
investigated in this study. This is done through a recently introduced quasi-2D
experimental-numerical framework that allows for a quantitative comparison of
the deformation fields of metal microstructures between experiments and
simulations at a high level of detail and complexity. The method exploits
samples that are locally ultra-thin (""2D"") and hence have a practically uniform
microstructure through their thickness. This allows testing more complex
loading conditions compared to uniaxial micromechanical experiments while
avoiding the complexity of an unknown subsurface microstructure, which limits
comparisons between experiments and simulations in traditional integrated
approaches at the level of the polycrystalline microstructure. The present
approach enables to study the effect of microstructural features such as grain
boundaries. To study the role of stochastic fluctuations, a constitutive model
is employed which introduces random heterogeneity into a crystal plasticity
model. A detailed analysis of the simulations is performed at the level of
individual slip systems. Since both experimental and numerical results are
susceptible to stochastic fluctuations, the outcomes of many simulations are
compared to the experimentally obtained result. This comparison allows us to
determine how a single experiment relates to an ensemble of simulations.
Additionally, results obtained with a conventional crystal plasticity model are
considered. The analysis reveals that the heterogeneity in the plasticity model
is essential for accurately capturing the deformation mechanisms.",2402.16199v1
2019-07-26,Stabilization of $\varepsilon$-Fe$_2$O$_3$ epitaxial layer on MgO(111)/GaN via an intermediate $γ$-Fe$_2$O$_3$-phase,"In the present study we have demonstrated epitaxial stabilization of the
metastable magnetically-hard $\varepsilon$-Fe$_2$O$_3$ phase on top of a thin
MgO(111) buffer layer grown onto the GaN (0001) surface. The primary purpose to
introduce a 4\,nm-thick buffer layer of MgO in between Fe$_2$O$_3$ and GaN was
to stop thermal migration of Ga into the iron oxide layer. Though such
migration and successive formation of the orthorhombic GaFeO$_3$ was supposed
earlier to be a potential trigger of the nucleation of the isostructural
$\varepsilon$-Fe$_2$O$_3$, the present work demonstrates that the growth of
single crystalline uniform films of epsilon ferrite by pulsed laser deposition
is possible even on the MgO capped GaN. The structural properties of the 60\,nm
thick Fe$_2$O$_3$ layer on MgO / GaN were probed by electron and x-ray
diffraction, both suggesting that the growth of $\varepsilon$-Fe$_2$O$_3$ is
preceded by formation of a thin layer of $\gamma$-Fe$_2$O$_3$. The presence of
the magnetically hard epsilon ferrite was independently confirmed by
temperature dependent magnetometry measurements. The depth-resolved x-ray and
polarized neutron reflectometry reveal that the 10\,nm iron oxide layer at the
interface has a lower density and a higher magnetization than the main volume
of the $\varepsilon$-Fe$_2$O$_3$ film. The density and magnetic moment depth
profiles derived from fitting the reflectometry data are in a good agreement
with the presence of the magnetically degraded $\gamma$-Fe$_2$O$_3$ transition
layer between MgO and $\varepsilon$-Fe$_2$O$_3$. The natural occurrence of the
interface between magnetoelectric $\varepsilon$- and spin caloritronic
$\gamma$- iron oxide phases can enable further opportunities to design novel
all-oxide-on-semiconductor devices.",1907.11611v2
2021-02-05,Inter-valence charge transfer and charge transport in the spinel ferrite ferromagnetic semiconductor Ru-doped CoFe$_2$O$_4$,"Inter-valence charge transfer (IVCT) is electron transfer between two metal
$M$ sites differing in oxidation states through a bridging ligand: $M^{n+1} +
M'^{m} \rightarrow M^{n} + M'^{m+1}$. It is considered that IVCT is related to
the hopping probability of electron (or the electron mobility) in solids. Since
controlling the conductivity of ferromagnetic semiconductors (FMSs) is a key
subject for the development of spintronic device applications, the manipulation
of the conductivity through IVCT may become a new approach of band engineering
in FMSs. In Ru-doped cobalt ferrite CoFe$_2$O$_4$ (CFO) that shows
ferrimagnetism and semiconducting transport properties, the reduction of the
electric resistivity is attributed to both the carrier doping caused by the Ru
substitution for Co and the increase of the carrier mobility due to
hybridization between the wide Ru $4d$ and the Fe $3d$ orbitals. The latter is
the so-called IVCT mechanism that is charge transfer between the mixed valence
Fe$^{2+}$/Fe$^{3+}$ states facilitated by bridging Ru $4d$ orbital: Fe$^{2+}$ +
Ru$^{4+}$ $\leftrightarrow$ Fe$^{3+}$ + Ru$^{3+}$. To elucidate the emergence
of the IVCT state, we have conducted x-ray absorption spectroscopy (XAS) and
resonant photoemission spectroscopy (RPES) measurements on non-doped CFO and
Co$_{0.5}$Ru$_{0.5}$Fe$_2$O$_4$ (CRFO) thin films. The observations of the XAS
and RPES spectra indicate that the presence of the mixed valence
Fe$^{2+}$/Fe$^{3+}$ state and the hybridization between the Fe $3d$ and Ru $4d$
states in the valence band. These results provide experimental evidence for the
IVCT state in CRFO, demonstrating a novel mechanism that controls the electron
mobility through hybridization between the $3d$ transition-metal cations with
intervening $4d$ states.",2102.03020v1
2021-02-24,"Gamma irradiated nanostructured NiFe2O4: Effect of gamma-photon on morphological, structural, optical and magnetic properties","The current manuscript highlights the preparation of NiFe2O4 nanoparticles by
adopting sol-gel auto combustion route. The prime focus of this study is to
investigate the impact of gamma irradiation on the microstructural,
morphological, functional, optical and magnetic characteristics. The resulted
NiFe2O4 products have been characterized employing numerous instrumental
equipments such as FESEM, XRD, UV visible spectroscopy, FTIR and PPMS for a
variety of gamma ray doses (0 kGy, 25 kGy and 100 kGy). FESEM micrographs
illustrate the aggregation of ferrite nanoparticles in pristine NiFe2O4 product
having an average particle size of 168 nm and the surface morphology is altered
after exposure to gamma-irradiation. XRD spectra have been analyzed employing
Rietveld method and the results of the XRD investigation reveal the desired
phases (cubic spinel phases) of NiFe2O4 with observing other transitional
phases. Several microstructural parameters such as bond length, bond angle,
hopping length etc. have been determined from the analysis of Rietveld method.
This study reports that the gamma irradiations demonstrate a great influence on
optical bandgap energy and it varies from 1.80 and 1.89 eV evaluated via K M
function. FTIR measurement depicts a proof for the persistence of Ni-O and Fe-O
stretching vibrations within the respective products and thus indicating the
successful development of NiFe2O4. The saturation magnetization (MS) of
pristine Ni ferrite product is noticed to be 28.08 emug-1. A considerable
increase in MS is observed in case of low gamma-dose (25 kGy) and a decrement
nature is disclosed after the result of high dose of gamma irradiation
(100kGy).",2102.12385v1
2021-05-19,Magnetic structure and multiferroicity of Sc-substituted hexagonal YbFeO$_3$,"Hexagonal rare-earth ferrite RFeO$_3$ family represents a unique class of
multiferroics exhibiting weak ferromagnetism, and a strong coupling between
magnetism and structural trimerization is predicted. However, the hexagonal
structure for RFeO$_3$ remains metastable in conventional condition. We have
succeeded in stabilizing the hexagonal structure of polycrystalline YbFeO$_3$
by partial Sc substitution of Yb. Using bulk magnetometry and neutron
diffraction, we find that Yb$_{0.42}$Sc$_{0.58}$FeO$_3$ orders into a canted
antiferromagnetic state with the Neel temperature $T_N$ ~ 165 K, below which
the $Fe^{3+}$ moments form the triangular configuration in the $ab$-plane and
their in-plane projections are parallel to the [100] axis, consistent with
magnetic space group $P$6$_{3}$$c'm'$. It is determined that the spin-canting
is aligned along the $c$-axis, giving rise to the weak ferromagnetism.
Furthermore, the $Fe^{3+}$ moments reorient toward a new direction below
reorientation temperature $T_R$ ~ 40 K, satisfying magnetic subgroup
$P$6$_{3}$, while the $Yb^{3+}$ moments order independently and
ferrimagnetically along the $c$-axis at the characteristic temperature $T_{Yb}$
~ 15 K. Interestingly, reproducible modulation of electric polarization induced
by magnetic field at low temperature is achieved, suggesting that the delicate
structural distortion associated with two-up/one-down buckling of the
Yb/Sc-planes and tilting of the FeO$_5$ bipyramids may mediate the coupling
between ferroelectric and magnetic orders under magnetic field. The present
work represents a substantial progress to search for high-temperature
multiferroics in hexagonal ferrites and related materials.",2105.08931v1
2022-01-18,"A Nanomechanical Testing Framework Yielding Front&Rear-Sided, High-Resolution, Microstructure-Correlated SEM-DIC Strain Fields","The continuous development of new multiphase alloys with improved mechanical
properties requires quantitative microstructure-resolved observation of the
nanoscale deformation mechanisms at, e.g., multiphase interfaces. This calls
for a combinatory approach beyond advanced testing methods such as microscale
strain mapping on bulk material and micrometer sized deformation tests of
single grains. We propose a nanomechanical testing framework that has been
carefully designed to integrate several state-of-the-art testing and
characterization methods: (i) well-defined nano-tensile testing of carefully
selected and isolated multiphase specimens, (ii) front&rear-sided SEM-EBSD
microstructural characterization combined with front&rear-sided in-situ SEM-DIC
testing at very high resolution enabled by a recently developed InSn nano-DIC
speckle pattern, (iii) optimized DIC strain mapping aided by application of SEM
scanning artefact correction and DIC deconvolution for improved spatial
resolution, (iv) a novel microstructure-to-strain alignment framework to
deliver front&rear-sided, nanoscale, microstructure-resolved strain fields, and
(v) direct comparison of microstructure, strain and SEM-BSE damage maps in the
deformed configuration. Demonstration on a micrometer-sized dual-phase steel
specimen, containing an incompatible ferrite-martensite interface, shows how
the nanoscale deformation mechanisms can be unraveled. Discrete
lath-boundary-aligned martensite strain localizations transit over the
interface into diffuse ferrite plasticity, revealed by the nanoscale
front&rear-sided microstructure-to-strain alignment and optimization of DIC
correlations. The proposed framework yields front&rear-sided aligned
microstructure and strain fields providing 3D interpretation of the deformation
and opening new opportunities for unprecedented validation of advanced
multiphase simulations.",2201.08249v2
2022-01-21,A Detailed Investigation of the Onion Structure of Exchanged Coupled Magnetic Fe(3-delta)O4@CoFe2O4@Fe(3-delta)O4 Nanoparticles,"Nanoparticles (NPs) which combine several magnetic phases offer wide
perspectives for cutting edge applications because of the high modularity of
their magnetic properties. Besides the addition of the magnetic characteristics
intrinsic to each phase, the interface that results from core-shell and,
further, from onion structures leads to synergistic properties such as magnetic
exchange coupling. Such a phenomenon is of high interest to overcome the
superparamagnetic limit of iron oxide NPs which hampers potential applications.
In this manuscript, we report on the design of NPs with an onion-like structure
which have been scarcely reported yet. These NPs consist in a Fe(3_delta)O4
core covered by a first shell of CoFe2O4 and a second shell of Fe(3-delta)O4.
They were synthesized by a multi-step seed mediated growth approach. Although
TEM micrographs clearly show the growth of each shell from the iron oxide core,
core sizes and shell thicknesses markedly differ from what is suggested by the
size increase. We investigated very precisely the structure of NPs in
performing high resolution (scanning) TEM imaging and GPA. The chemical
composition and spatial distribution of atoms were studied by EELS. The
chemical environment and oxidation state of cations were investigated by
M\""ossbauer spectrometry, soft XAS and XMCD. These techniques allowed us to
estimate the increase of Fe2+ content in the iron oxide core of the core@shell
structure and the increase of the cobalt ferrite shell thickness in the
core@shell@shell one, while the iron oxide shell appears to be much thinner
than expected. Thus, the modification of the chemical composition as well as
the size of the Fe(3-delta)O4 core and the thickness of the cobalt ferrite
shell have a high impact on the magnetic properties. Furthermore, the growth of
the iron oxide shell also markedly modifies the magnetic properties of the
core-shell NPs.",2201.08923v1
2023-06-19,Onion-like Fe3O4/MgO/CoFe2O4 magnetic nanoparticles: new ways to control magnetic coupling between soft/hard phases,"The control of the magnetization inversion dynamics is one of the main
challenges driving the design of new nanostructured magnetic materials for
magnetoelectronic applications. Nanoparticles with onion-like architecture
offer a unique opportunity to expand the possibilities allowing to combine
different phases at the nanoscale and also modulate the coupling between
magnetic phases by introducing spacers in the same structure. Here we report
the fabrication, by a three-step high temperature decomposition method, of
Fe3O4/MgO/CoFe2O4 onio-like nanoparticles and their detailed structural
analysis, elemental compositional maps and magnetic response. The
core/shell/shell nanoparticles present epitaxial growth and cubic shape with
overall size of (29+-6) nm. These nanoparticles are formed by cubic iron oxide
core of (22+-4) nm covered by two shells, the inner of magnesium oxide and the
outer of cobalt ferrite of ~1 and ~2.5 nm of thickness, respectively. The
magnetization measurements show a single reversion magnetization curve and the
enhancement of the coercivity field, from HC~608 Oe for the Fe3O4/MgO to
HC~5890 Oe to the Fe3O4/MgO/CoFe2O4 nanoparticles at T=5 K, ascribed to the
coupling between both ferrimagnetic phases with a coupling constant of =2
erg/cm2. The system also exhibits exchange bias effect, where the exchange bias
field increases up to HEB~2850 Oe at 5 K accompanied with the broadening of the
magnetization loop of HC~6650 Oe. This exchange bias effect originates from the
freezing of the surface spins below the freezing temperature TF=32 K that
pinned the magnetic moment of the cobalt ferrite shell.",2306.13108v1
2023-06-29,Registration between DCT and EBSD datasets for multiphase microstructures,"The ability to characterise the three-dimensional microstructure of
multiphase materials is essential for understanding the interaction between
phases and associated materials properties. Here, laboratory-based
diffraction-contrast tomography (DCT), a recently-established materials
characterization technique that can determine grain phases, morphologies,
positions and orientations in a voxel-based reconstruction method, was used to
map part of a dual-phase steel alloy sample. To assess the resulting
microstructures that were produced by the DCT technique, an EBSD map was
collected within the same sample volume. To identify the 2D slice of the 3D DCT
reconstruction that best corresponded to the EBSD map, a novel registration
technique based solely on grain-averaged orientations was developed -- this
registration technique requires very little a priori knowledge of dataset
alignment and can be extended to other techniques that only recover
grain-averaged orientation data such as far-field 3D X-ray diffraction
microscopy. Once the corresponding 2D slice was identified in the DCT dataset,
comparisons of phase balance, grain size, shape and texture were performed
between DCT and EBSD techniques. More complicated aspects of the
microstructural morphology such as grain boundary shape and grains less than a
critical size were poorly reproduced by the DCT reconstruction, primarily due
to the difference in resolutions of the technique compared with EBSD. However,
lab-based DCT is shown to accurately determine the centre-of-mass position,
orientation, and size of the large grains for each phase present, austenite and
martensitic ferrite. The results reveals a complex ferrite grain network of
similar crystal orientations that are absent from the EBSD dataset. Such detail
demonstrates that lab-based DCT, as a technique, shows great promise in the
field of multi-phase material characterization.",2306.17011v1
2023-09-19,Remanence Increase in SrFe$_{12}$O$_{19}$/Fe Exchange-Decoupled Hard-Soft Composite Magnets Owing to Dipolar Interactions,"In the search for improved permanent magnets, fueled by the geostrategic and
environmental issues associated with rare-earth-based magnets, magnetically
hard (high anisotropy)-soft (high magnetization) composite magnets hold promise
as alternative magnets that could replace modern permanent magnets, such as
rare-earth-based and ceramic magnets, in certain applications. However, so far,
the magnetic properties reported for hard-soft composites have been
underwhelming. Here, an attempt to further understand the correlation between
magnetic and microstructural properties in strontium ferrite-based composites,
hard SrFe$_{12}$O$_{19}$ (SFO) ceramics with different contents of Fe particles
as soft phase, both in powder and in dense injection molded magnets, is
presented. In addition, the influence of soft phase particle dimension, in the
nano- and micron-sized regimes, on these properties is studied. While Fe and
SFO are not exchange-coupled in our magnets, a remanence that is higher than
expected is measured. In fact, in composite injection molded anisotropic
(magnetically oriented) magnets, remanence is improved by 2.4% with respect to
a pure ferrite identical magnet. The analysis of the experimental results in
combination with micromagnetic simulations allows us to establish that the type
of interaction between hard and soft phases is of a dipolar nature, and is
responsible for the alignment of a fraction of the soft spins with the
magnetization of the hard. The mechanism unraveled in this work has
implications for the development of novel hard-soft permanent magnets.",2309.10676v1
2024-03-07,"Effects of mechanical stress, chemical potential, and coverage on hydrogen solubility during hydrogen enhanced decohesion of ferritic steel grain boundaries: A first-principles study","Hydrogen enhanced decohesion (HEDE) is one of the many mechanisms of hydrogen
embrittlement, a phenomenon which severely impacts structural materials such as
iron and iron alloys. Grain boundaries (GBs) play a critical role in this
mechanism, where they can provide trapping sites or act as hydrogen diffusion
pathways. The interaction of H with GBs and other crystallographic defects, and
thus the solubility and distribution of H in the microstructure, depends on the
concentration, chemical potential and local stress. Therefore, for a
quantitative assessment of HEDE, a generalized solution energy in conjunction
with the cohesive strength as a function of hydrogen coverage is needed. In
this work, we carry out density functional theory calculations to investigate
the influence of H on the decohesion of the $\Sigma$5(310)[001] and
$\Sigma$3(112)[1$\bar{1}$0] symmetrical tilt GBs in bcc Fe, as examples for
open and close-packed GB structures. A method to identify the segregation sites
at the GB plane is proposed. The results indicate that at higher local
concentrations, H leads to a significant reduction of the cohesive strength of
the GB planes, significantly more pronounced at the $\Sigma$5 than at the
$\Sigma$3 GB. Interestingly, at finite stress the $\Sigma$3 GB becomes more
favorable for H solution, as opposed to the case of zero stress, where the
$\Sigma$5 GB is more attractive. This suggests that under certain conditions
stresses in the microstructure can lead to a re-distribution of H to the
stronger grain boundary, which opens a new path to designing H-resistant
microstructures. To round up our study, we investigate the effects of typical
alloying elements in ferritic steel, C, V, Cr and Mn, on the solubility of H
and the strength of the GBs.",2403.04741v1
1998-06-24,A Scanned Perturbation Technique For Imaging Electromagnetic Standing Wave Patterns of Microwave Cavities,"We have developed a method to measure the electric field standing wave
distributions in a microwave resonator using a scanned perturbation technique.
Fast and reliable solutions to the Helmholtz equation (and to the Schrodinger
equation for two dimensional systems) with arbitrarily-shaped boundaries are
obtained. We use a pin perturbation to image primarily the microwave electric
field amplitude, and we demonstrate the ability to image broken time-reversal
symmetry standing wave patterns produced with a magnetized ferrite in the
cavity. The whole cavity, including areas very close to the walls, can be
imaged using this technique with high spatial resolution over a broad range of
frequencies.",9806023v1
2002-06-21,Multiple bound states in scissor-shaped waveguides,"We study bound states of the two-dimensional Helmholtz equations with
Dirichlet boundary conditions in an open geometry given by two straight leads
of the same width which cross at an angle $\theta$. Such a four-terminal
junction with a tunable $\theta$ can realized experimentally if a right-angle
structure is filled by a ferrite. It is known that for $\theta=90^o$ there is
one proper bound state and one eigenvalue embedded in the continuum. We show
that the number of eigenvalues becomes larger with increasing asymmetry and the
bound-state energies are increasing as functions of $\theta$ in the interval
$(0,90^o)$. Moreover, states which are sufficiently strongly bent exist in
pairs with a small energy difference and opposite parities. Finally, we discuss
how with increasing $\theta$ the bound states transform into the quasi-bound
states with a complex wave vector.",0206397v2
2003-01-22,Current and vorticity auto correlation functions in open microwave billiards,"Using the equivalence between the quantum-mechanical probability density in a
quantum billiard and the Poynting vector in the corresponding microwave system,
current distributions were studied in a quantum dot like cavity, as well as in
a Robnik billiard with lambda=0.4, and an introduced ferrite cylinder. Spatial
auto correlation functions for currents and vorticity were studied and compared
with predictions from the random-superposition-of-plane-waves hypothesis. In
addition different types of vortex neighbour spacing distributions were
determined and compared with theory.",0301411v2
2004-03-15,Superparamagnetic relaxation in Cu_{x}Fe_{3-x}O_{4} (x=0.5 and x=1) nanoparticles,"The scope of this article is to report very detailed results of the
measurements of magnetic relaxation phenomena in the new
Cu$_{0.5}$Fe$_{2.5}$O$_{4}$ nanoparticles and known CuFe$_{2}$O$_{4}$
nanoparticles. The size of synthesized particles is (6.5$\pm $1.5)nm. Both
samples show the superparamagnetic behaviour, with the well-defined phenomena
of blocking of magnetic moment. This includes the splitting of
zero-field-cooled and field-cooled magnetic moment curves, dynamical
hysteresis, slow quasi-logarithmic relaxation of magnetic moment below blocking
temperature. The scaling of the magnetic moment relaxation data at different
temperatures confirms the applicability of the simple thermal relaxation model.
The two copper-ferrites with similar structures show significantly different
magnetic anisotropy density and other magnetic properties. Investigated systems
exhibit the consistency of all obtained results.",0403358v1
2004-06-30,Weak ferromagnetism and magnetoelectric coupling in bismuth ferrite,"We analyze the coupling between the ferroelectric and magnetic order
parameters in the magnetoelectric multiferroic BiFeO_3 using density functional
theory within the local spin density approximation and the LSDA+U method. We
show that weak ferromagnetism of the Dzyaloshinskii-Moriya type occurs in this
material, and we analyze the coupling between the resulting magnetization and
the structural distortions. We explore the possibility of
electric-field-induced magnetization reversal and show that, although it is
unlikely to be realized in BiFeO_3, it is not in general impossible. Finally we
outline the conditions that must be fulfilled to achieve switching of the
magnetization using an electric field.",0407003v1
2004-12-13,Space-Time Parity Violation and Magnetoelectric Interactions in Antiferromagnets,"The properties of antiferromagnetic materials with violated space-time parity
are considered. Particular attention is given to the bismuth ferrite BiFeO3
ferroelectric magnet. This material is distinguished from other
antiferromagnets in that the inversion center is absent in its crystal and
magnetic structures. This circumstance gives rise to the diversified and
unusual properties, namely, to the appearance of a spatially modulated spin
structure and to the unique possibility of the linear magnetoelectric effect
coexisting with a weak ferromagnetic moment. The magnetic-induced phase
transitions accompanied by the suppression of the modulated spin structure and
appearance of a number of new and unusual effects are considered. These are the
linear magnetoelectric effect and the appearance of a toroidal moment and a
weak ferromagnetic moment of the magnetoelectric nature.",0412318v1
2005-05-06,Oxygen diffusion in nanostructured perovskites,"Nonstoichiometric perovskite-related oxides (such as ferrites and cobaltites,
etc.) are characterized by fast oxygen transport at ambient temperatures, which
relates to the microstructural texturing of these materials, consisting wholly
of nanoscale microdomains.
  We have developed an inhomogeneous diffusion model to describe the kinetics
of oxygen incorporation into nanostructured oxides. Nanodomain boundaries are
assumed to be the high diffusivity paths for oxygen transport whereas diffusion
into the domains proceeds much slower. Using Laplace transform methods, an
exact solution is found for a ramped stepwise potential, allowing fitting of
the experimental data to theoretical curves (in Laplace transforms).
  A further model generalization is considered by introducing additional
parameters for the size distribution of domains and particles.
  The model has been applied for qualitative evaluation of oxygen diffusion
parameters from the data on wet electrochemical oxidation of nano-structured
perovskite SrCo_0.5Fe_0.2Ta_0.3O_{3-y} samples.",0505149v2
2006-02-27,Excitation of vortices using linear and nonlinear magnetostatic waves,"It is shown that stationary vortex structures can be excited in a ferrite
film. This is the first proposal for creating vortex structures in the
important cm and mm wavelength ranges. It is shown that both linear and
nonlinear structures can be excited using a three-beam interaction created with
circular antennae. These give rise to a special phase distribution created by
linear and nonlinear mixing. An interesting set of three clockwise rotating
vortices joined by one counter-rotating one presents itself in the linear
regime: a scenario that is only qualitatively changed by the onset of
nonlinearity. It is pointed out that control of the vortex structure, through
parametric coupling, based upon a microwave resonator, is possible and that
there are many interesting possibilities for applications.",0602637v1
2007-01-14,Sr1.5Ba0.5Zn2Fe12O22 Hexaferrites Ferromagnetic Resonance and Nonlinear Excitation for Magneto-Electric Devices,"A magneto electric (ME) effect was reported [1] for the insulator material of
helimagnetic hexaferrite of Sr1.5Ba0.5Zn2Fe12O22. In this study we are
interested in investigating this materials ferromagnetic resonance to define
its internal anisotropy fields. By using a vibrating sample magnetometer (VSM)
and ferromagnetic resonance (FMR) analysis we realized that this helical
hexaferrite has about -0.5 kOe exchange anisotropy field of HE. Also, by using
an alternative free energy model we derived this materials Polder tensor and
its ferromagnetic resonance condition. Meanwhile, we were able to show a
potential magneto electric coupling by nonlinear excitation of planar helical
hexaferrite, in which a magnetic nonlinear excitation is integrated into
dielectric permittivity.
  Index Terms, Ferrites, ferromagnetic resonances, and magnetic nonlinear
excitations.",0701309v2
2007-01-29,Parameters of the Dzyaloshinsky-Moriya type weak ferromagnetism for some perovskite compounds,"Compounds with distorted perovskite structure of the 4-f and 3-d transition
metals with the common formula LnTO3 (where Ln is rare-earth element, T is an
element from the Fe group) are the most multifold binary oxides of these two
groups elements. Wide range of stability for this structure allows the
realization of combinations of the Lanthanides with all the transition metals
except the Nickel. Quite interesting physical phenomena take place in these
oxides like charge and orbital ordering; relatively independent magnetic
lattices of the both metals; particular magnetic structures; high optical
indicators; giant magneto-resistance; peculiar dielectric and ferroelectric
properties etc. We have investigated the magnetic properties of pure ferrites
and chromium-based materials as well as of some mixed type oxides like
HoxTb1-xO3, HoMnxFe1-xO3, HoMnxCr1-xO3 and DyFexCr1-xO3.",0701708v1
2006-04-13,Exchange Bias and Vertical Shift in CoFe2O4 nanoparticles,"Magnetic properties of core-shell cobalt ferrite nanoparticles 15 to 48nm
prepared by a sol-gel route have been studied. It is shown that the coercivity
follows non-monotonic size dependence varying as 1/d above the maximum (d is
the particle size). Field cooled magnetization exhibited both horizontal
(exchange bias) and vertical shifts. The exchange bias is understood as
originating at the interface between a surface region with structural and spin
disorder and a core ferrimagnetic region. The dependence of the exchange bias
and vertical shifts on the particle sizes and cooling fields are found to have
significant differences and the differences are explained in the light of
recent results which suggest that both weakly and strongly pinned spins are
present at the interface. It is suggested that the exchange bias is dominated
by the weakly pinned spins while the vertical shift is affected by the strongly
pinned ones.",0604027v1
2000-08-17,RF Cell Modeling and Experiments for Wakefield Minimization in DARHT-II,"Electron beams of linear induction accelerators experience deflective forces
caused by RF fields building up as a result of accelerating cavities of finite
size. These forces can significantly effect the beam when a long linac composed
of identical cells is assembled. Recent techniques in computational modeling,
simulation, and experiments for 20 MeV DARHT-II (Dual Axis Radiographic
Hydrodynamic Test) accelerator cells were found to reduce the wakefield
impedance of the cells from 800 ohms/meter to 350 ohms/meter and experimental
results confirm the results of the modeling efforts. Increased performance of
the cell was obtained through a parametric study of the accelerator structure,
materials, material tuning, and geometry. As a result of this effort, it was
found that thickness-tuned ferrite produced a 50% deduction in the wakefield
impedance in the low frequency band and was easily tunable based on the
material thickness. It was also found that shaped metal sections allow for
high-Q resonances to be de-tuned, thus decreasing the amplitude of the
resonance and increasing the cell s performance. For the geometries used for
this cell, a roughly 45 degree angle had the best performance in affecting the
wakefield modes.",0008099v2
2004-12-14,"Effects of Static Magnetic Field on Growth of Leptospire, Leptospira interrogans serovar canicola: Immunoreactivity and Cell Division","The effects of the exposure of the bacterium, Leptospira interrogans serovar
canicola to a constant magnetic field with magnetic flux density from a
permanent ferrite magnet = 140 mT were studied. Changes in Leptospira cells
after their exposure to the field were determined on the basis of changes in
their growth behavior and agglutination immunoreactivity with a homologous
antiserum using darkfield microscopy together with visual imaging. The data
showed that the exposed Leptospira cells have lower densities and lower
agglutination immunoreactivity than the unexposed control group. Interestingly,
some of the exposed Leptospira cells showed abnormal morphologies such as large
lengths. We discussed some of the possible reasons for these observations.",0412076v1
2007-07-26,Room temperature spin filtering in epitaxial cobalt-ferrite tunnel barriers,"We report direct experimental evidence of room temperature spin filtering in
magnetic tunnel junctions (MTJs) containing CoFe2O4 tunnel barriers via
tunneling magnetoresistance (TMR) measurements.
Pt(111)/CoFe2O4(111)/gamma-Al2O3(111)/Co(0001) fully epitaxial MTJs were grown
in order to obtain a high quality system, capable of functioning at room
temperature. Spin polarized transport measurements reveal significant TMR
values of -18% at 2 K and -3% at 290 K. In addition, the TMR ratio follows a
unique bias voltage dependence that has been theoretically predicted to be the
signature of spin filtering in MTJs containing magnetic barriers. CoFe2O4
tunnel barriers therefore provide a model system to investigate spin filtering
in a wide range of temperatures.",0707.3823v2
2007-11-26,Electronic structures and lattice dynamics of BaTiO3 and BiFeO3 : a comparative first-principles study,"First-principles calculations were performed to investigate the ferroelectric
properties of barium titanate and bismuth ferrite, as well as phonon dispersion
of BaTiO3, using density functional theory and density functional perturbation
theory. Results show that the strong hybridization of Ti-O and Bi-O lead to the
corresponding mechanisms for stabilizing the distorted structure. The
spontaneous polarization of 59.4 \mu C/cm2 and 27.6 \mu C/cm2 were calculated
for BiFeO3 and BaTiO3 respectively, using berry phase method within the modern
theory of polarization. The stereochemical activity of Bi-6s long-pair, which
was the driven mechanism for ferroelectricity in BiFeO3, was able to produce
greater polarization than the Ti off-centring displacement in BaTiO3. New
multiferroic perovskite type materials combined with these two ferroelectric
instabilities were predicted to have a better ferromagnetic ordering in
comparison with BiFeO3.",0711.3942v3
2008-01-10,Linear and Nonlinear Optical constants of BiFeO_3,"Using spectroscopic ellipsometry, the refractive index and absorption versus
wavelength of the ferroelectric antiferromagnet Bismuth Ferrite, BiFeO_3 is
reported. The material has a direct band-gap at 442 nm wavelength (2.81 eV).
Using optical second harmonic generation, the nonlinear optical coefficients
were determined to be d_15/d_22 = 0.20 +/- 0.01, d_31/d_22 = 0.35 +/- 0.02,
d_33/d_22 = -11.4 +/- 0.20 and |d_22| = 298.4 +/- 6.1 pm/V at a fundamental
wavelength of 800 nm.",0801.1626v1
2008-04-28,The role of carbon segregation on nanocrystallisation of pearlitic steels processed by severe plastic deformation,"The nanostructure and the carbon distribution in a pearlitic steel processed
by torsion under high pressure was investigated by three-dimensional atom
probe. In the early stage of deformation (shear strain of 62),
off-stoichiometry cementite was analysed close to interphase boundaries and a
strong segregation of carbon atoms along dislocation cell boundaries was
observed in the ferrite. At a shear strain of 300, only few nanoscaled
off-stoichiometry cementite particles remain and a nanoscaled equiaxed grain
structure with a grain size of about 20 nm was revealed. 3D-AP data clearly
point out a strong segregation of carbon atoms along grain boundaries. The
influence of this carbon atom segregation on the nanostructure formation is
discussed and a scenario accounting for the nanocrystallisation during severe
plastic deformation is proposed.",0804.4377v1
2008-06-30,Beam Coupling Impedance Measurement and Mitigation for a TOTEM Roman Pot,"The longitudinal and transverse beam coupling impedance of the first final
TOTEM Roman Pot unit has been measured in the laboratory with the wire method.
For the evaluation of transverse impedance the wire position has been kept
constant, and the insertions of the RP were moved asymmetrically. With the
original configuration of the RP, resonances with fairly high Q values were
observed. In order to mitigate this problem, RF-absorbing ferrite plates were
mounted in appropriate locations. As a result, all resonances were sufficiently
damped to meet the stringent LHC beam coupling impedance requirements.",0806.4974v1
2008-09-02,Parametrically-stimulated recovery of a microwave signal using standing spin-wave modes of a magnetic film,"The phenomenon of storage and parametrically-stimulated recovery of a
microwave signal in a ferrite film has been studied both experimentally and
theoretically. The microwave signal is stored in the form of standing spin-wave
modes existing in the film due to its finite thickness. Signal recovery is
performed by means of frequency-selective amplification of one of these
standing modes by double- requency parametric pumping process. The time of
recovery, as well as the duration and magnitude of the recovered signal, depend
on the timing and amplitudes of both the input and pumping pulses. A mean-field
theory of the recovery process based on the competitive interaction of the
signal-induced standing spin-wave mode and thermal magnons with the parametric
pumping field is developed and compared to the experimental data.",0809.0395v1
2008-10-15,Magnetic susceptibility and magnetization fluctuation measurements of mixed Gadolinium-Yttrium Iron Garnets,"We study the magnetic properties of Gadolinium-Yttrium Iron Garnet
($\text{Gd}_{x}\text{Y}_{3-x}\text{Fe}_5\text{0}_{12}$, $x=3,1.8$) ferrite
ceramics. The complex initial permeability is measured in the temperature range
2 K to 295 K at frequency of 1 kHz, and in the frequency range 100 Hz to 200
MHz at temperatures 4 K, 77 K, and 295 K. The magnetic viscosity-induced
imaginary part of the permeability is observed at low frequencies. Measurements
of the magnetization noise are made at 4 K. Using the fluctuation-dissipation
theorem, we find that the observed magnetization fluctuations are consistent
with our measurements of the low-frequency imaginary part of permeability. We
discuss some implications for proposed precision measurements as well as other
possible applications.",0810.2770v1
2008-12-02,"Phase transitions in multiferroic BiFeO3 crystals, thin-layers, and ceramics: Enduring potential for a single phase, room-temperature magnetoelectric 'holy grail'","Magnetic phase transitions in multiferroic bismuth ferrite (BiFeO3) induced
by magnetic field, epitaxial strain, and composition modification are
considered. These transitions from a spatially modulated spin spiral state to a
homogenous antiferromagnetic one are accompanied by the release of latent
magnetization and a linear magnetoelectric effect that makes BiFeO3-based
materials efficient room-temperature single phase multiferroics.",0812.0484v2
2008-12-24,Design and optimization of one-dimensional ferrite-film based magnonic crystals,"One-dimensional magnonic crystals have been implemented as gratings of
shallow grooves chemically etched into the surface of yttrium-iron garnet
films. Scattering of backward volume magnetostatic spin waves from such
structures is investigated experimentally and theoretically. Well-defined
rejection frequency bands are observed in transmission characteristics of the
magnonic crystals. The loss inserted by the gratings and the rejections bands
bandwidths are studied as a function of the film thickness, the groove depth,
the number of grooves, and the groove width. The experimental data are well
described by a theoretical model based on the analogy of a spin-wave
film-waveguide with a microwave transmission line. Our study shows that
magnonic crystals with required operational characteristics can be engineered
by adjusting these geometrical parameters.",0812.4553v1
2009-01-23,Structural Origin of the Metal-Insulator Transition of Multiferroic BiFeO3,"We report X-ray structural studies of the metal-insulator phase transition in
bismuth ferrite, BiFeO3, both as a function of temperature and of pressure (931
oC at atmospheric pressure and ca. 45 GPa at ambient temperature). Based on the
experimental results, we argue that the metallic gamma-phase is not
rhombohedral but is instead the same cubic Pm3m structure whether obtained via
high temperature or high pressure, that the MI transition is second order or
very nearly so, that this is a band-type transition due to semi-metal band
overlap in the cubic phase and not a Mott transition, and that it is primarily
structural and not an S=5/2 to S=1/2 high-spin/low-spin electronic transition.
Our data are compatible with the orthorhombic Pbnm structure for the beta-phase
determined definitively by the neutron scattering study of Arnold et al .[Phys.
Rev. Lett. 2009]; the details of this beta-phase had also been controversial,
with a remarkable collection of five crystal classes (cubic, tetragonal,
orthorhombic, monoclinic, and rhombohedral!) all claimed in recent
publications.",0901.3748v2
2009-04-02,Current-controlled dynamic magnonic crystal,"We demonstrate a current-controlled, dynamic magnonic crystal. It consists of
a ferrite film whose internal magnetic field exhibits a periodic, cosine-like
variation. The field modulation is created by a direct current flowing through
an array of parallel wires placed on top of a spin-wave waveguide. A single,
pronounced rejection band in the spin-wave transmission characteristics is
formed due to spin-wave scattering from the inhomogeneous magnetic field. With
increasing current the rejection band depth and its width increase strongly.
The magnonic crystal allows a fast control of its operational characteristics
via the applied direct current. Simulations confirm the experimental results.",0904.0332v1
2009-09-27,Strain-induced isosymmetric phase transition in BiFeO3,"We calculate the effect of epitaxial strain on the structure and properties
of multiferroic bismuth ferrite, BiFeO3, using first-principles density
functional theory. We find that, while small strains cause only quantitative
changes in behavior from the bulk material, compressive strains of greater than
4% induce an isosymmetric phase transition accompanied by a dramatic change in
structure. In striking contrast to the bulk rhombohedral perovskite, the highly
strained structure has a c/a ratio of ~1.3 and five-coordinated Fe atoms. We
predict a rotation of polarization from [111] (bulk) to nearly [001],
accompanied by an increase in magnitude of ~50%, and a suppression of the
magnetic ordering temperature. Intriguingly, our calculations indicate critical
strain values at which the two phases might be expected to coexist.",0909.4979v4
2009-09-29,First-principles study of ferroelectric domain walls in multiferroic bismuth ferrite,"We present a first-principles density functional study of the structural,
electronic and magnetic properties of the ferroelectric domain walls in
multiferroic BiFeO3. We find that domain walls in which the rotations of the
oxygen octahedra do not change their phase when the polarization reorients are
the most favorable, and of these the 109 degree domain wall centered around the
BiO plane has the lowest energy. The 109 degree and 180 degree walls have a
significant change in the component of their polarization perpendicular to the
wall; the corresponding step in the electrostatic potential is consistent with
a recent report of electrical conductivity at the domain walls. Finally, we
show that changes in the Fe-O-Fe bond angles at the domain walls cause changes
in the canting of the Fe magnetic moments which can enhance the local
magnetization at the domain walls.",0909.5294v1
2009-10-30,Charge and orbital ordering in Fe and Mn perovskite oxides far from half- doping by resonant x- ray scattering,"The emergence of superlattice periodicities at metal to insulator transitions
in hole doped perovskite oxides responds to a rearrangement of the local atomic
structure, and electron and spin density distribution. Originally, the ionic
model based on a checkerboard- type atomic distribution served to describe the
low temperature charge and orbital ordered (COO) phases arising in half- doped
manganites. In the last years, the exploitation of resonant x- ray scattering
(RXS) capabilities has shown the need to revisit these concepts and improve the
picture. Yet, we have realised that COO is a more common phenomenon than
expected that can be observed in a wide range of doping levels. Here we compare
the experimental data recently collected by RXS on La_0.4Sr_1.6MnO_4 (x=0.60)
and La(Pr)_1/3Sr_2/3FeO_3 (x=0.67). The first shows a COO phase similar to that
found in the x=0.5 sample but angular peak positions vs. T denotes the
incommensurability of superlattice reflections. Meanwhile, the analysis of the
commensurate CO phase in the studied ferrite underlines the role of the
structural changes also involving La(Sr) and O atoms.",0910.5788v1
2010-02-04,Polarization transformations by a magneto-photonic layered structure in vicinity of ferromagnetic resonance,"The polarization properties of a magnetophotonic crystal at the frequencies
located in the vicinity of ferromagnetic resonance are studied. The
investigations are curried out taking into consideration the fact that the
magnitude of material losses in ferrite layers at this frequency band is
significant. The method is based on obtaining a system of ordinary differential
equations and further analyzing the stability of solutions of this system. The
electromagnetic properties of the structure under study are found out via the
analysis of the eigenvalues of the transfer matrix of the structure period. On
this basis the boundaries of the stopbands and passbands of the eigenwaves are
determined. The frequency and angular dependences of the reflection and
transmission coefficients are given. The angle of the rotation of the
polarization plane and the ellipticity of the reflected and transmitted fields
are obtained.",1002.1087v2
2010-06-16,Sub-monolayers of carbon on alpha-iron facets: an ab-initio study,"Motivated by recent in situ studies of carbon nanotube growth from large
transition-metal nanoparticles, we study various alpha-iron (ferrite) facets at
different carbon concentrations using ab initio methods. The studied (110),
(100) and (111) facets show qualitatively different behaviour when carbon
concentration changes. In particular, adsorbed carbon atoms repel each other on
the (110) facet, resulting in carbon dimer and graphitic material formation.
Carbon on the (100) facet forms stable structures at concentrations of about
0.5 monolayer and at 1.0 monolayer this facet becomes unstable due to a
frustration of the top layer iron atoms. The stability of the (111) facet is
weakly affected by the amount of adsorbed carbon and its stability increases
further with respect to the (100) facet with increasing carbon concentration.
The exchange of carbon atoms between the surface and sub-surface regions on the
(111) facet is easier than on the other facets and the formation of carbon
dimers is exothermic. These findings are in accordance with a recent in situ
experimental study where the existence of graphene decorated (111) facets is
related to increased carbon concentration.",1006.3187v1
2010-08-17,Imaging ferroelectric domains in multiferroics using a low-energy electron microscope in the mirror operation mode,"We report on low-energy electron microscopy imaging of ferroelectric domains
with submicron resolution. Periodic strips of 'up' and 'down'-polarized
ferroelectric domains in bismuth ferrite -a room temperature multiferroic-
serve as a model system to compare low-energy electron microscopy with the
established piezoresponse force microscopy. The results confirm the possibility
of full-field imaging of ferroelectric domains with short acquisition times by
exploiting the sensitivity of ultraslow electrons to small variations of the
electric potential near surfaces in the ""mirror"" operation mode.",1008.2861v1
2010-11-08,Calculation of the substitutional fraction of ion-implanted He in an Fe target,"Ion-implantation is a useful technique to study irradiation damage in nuclear
materials. To study He effects in nuclear fusion conditions, He is co-implanted
with damage ions to reproduce the correct He/dpa ratios in the desired or
available depth range. However, the short-term fate of these He ions, i.e over
the time scales of their own collisional phase, has not been yet unequivocally
established. Here we present an atomistic study of the short-term evolution of
He implantation in an Fe substrate to approximate the conditions encountered in
dual ion-implantation studies in ferritic materials. Specifically, we calculate
the fraction of He atoms that end up in substitutional sites shortly after
implantation, i.e. before they contribute to long-term miscrostructural
evolution. We find that fractions of at most 3% should be expected for most
implantation studies. In addition, we carry out an exhaustive calculation of
interstitial He migration energy barriers in the vicinity of matrix vacancies
and find that they vary from approximately 20 to 60 meV depending on the
separation and orientation of the He-vacancy pair.",1011.1867v1
2010-12-14,Scaling behavior of the spin pumping effect in ferromagnet/platinum bilayers,"We systematically measured the DC voltage V_ISH induced by spin pumping
together with the inverse spin Hall effect in ferromagnet/platinum bilayer
films. In all our samples, comprising ferromagnetic 3d transition metals,
Heusler compounds, ferrite spinel oxides, and magnetic semiconductors, V_ISH
invariably has the same polarity. V_ISH furthermore scales with the
magnetization precession cone angle with a universal prefactor, irrespective of
the magnetic properties, the charge carrier transport mechanism or type. These
findings quantitatively corroborate the present theoretical understanding of
spin pumping in combination with the inverse spin Hall effect.",1012.3017v2
2011-02-02,Interstitial Fe-Cr alloys: Tuning of magnetism by nanoscale structural control and by implantation of nonmagnetic atoms,"Using the density functional theory, we perform a full atomic relaxation of
the bulk ferrite with 12.5%-concentration of monoatomic interstitial Cr
periodically located at the edges of the bcc Fe$_\alpha$ cell. We show that
structural relaxation in such artificially engineered alloys leads to
significant atomic displacements and results in the formation of novel highly
stable configurations with parallel chains of octahedrically arranged Fe. The
enhanced magnetic polarization in the low-symmetry metallic state of this type
of alloys can be externally controlled by additional inclusion of nonmagnetic
impurities like nitrogen. We discuss possible applications of generated
interstitial alloys in spintronic devices and propose to consider them as a
basis of novel durable types of stainless steels.",1102.0432v2
2011-02-21,"The energetic and structural properties of bcc NiCu, FeCu alloys: a first-principles study","Using special quasirandom structures (SQS's), we perform first-principles
calculations studying the metastable bcc NiCu and FeCu alloys which occur in
Fe-Cu-Ni alloy steels as precipitated second phase. The mixing enthalpies,
density of state, and equilibrium lattice parameters of these alloys are
reported. The results show that quasi-chemical approach and vegard rule can
well predict the energetic and structural properties of FeCu alloys but fail to
yield that of NiCu. The reason rests with the difference of bond energy
variation with composition between NiCu and FeCu alloys induced by competition
between ferromagnetic and paramagnetic state. Furthermore, the calculated
results show that the energetic and structural properties of these alloys can
well explain the local composition of the corresponding precipitates in ferrite
steels.",1102.4115v2
2011-03-22,Magnetic Interactions in Ball-Milled Spinel Ferrites,"Spinel Fe3O4 nanoparticles have been produced through ball milling in
methyl-alcohol (CH3OH), aiming to obtain samples with similar average particle
sizes <d> and different interparticle interactions. Three samples having
Fe3O4/CH3(OH) mass ratios R of 3 %, 10 % and 50 % wt. were milled for several
hours until particle size reached a steady value (<d> ~ 7-10 nm). A detailed
study of static and dynamic magnetic properties has been undertaken by
measuring magnetization, ac susceptibility and M\""ossbauer data. As expected
for small particles, the Verwey transition was not observed, but instead
superparamagnetic (SPM) behavior was found with transition to a blocked state
at TB ~ 10-20 K. Spin disorder of the resulting particles, independent of its
concentration, was inferred from the decrease of saturation magnetization MS at
low temperatures. For samples having 3% wt. of magnetic particles, dynamic ac
susceptibility measurements show a thermally activated Arrhenius dependence of
the blocking temperature with applied frequency. This behaviour is found to
change as interparticle interactions begin to rule the dynamics of the system,
yielding a spin-glass-like state at low temperatures for R = 50 wt.% sample.",1103.4390v1
2011-07-19,Composition Dependence of Structural Parameters and Properties of Gallium Ferrite,"We show the effect of composition on structural and magnetic characteristics
of pure phase polycrystalline Ga<2-x>Fe<x>O<3> (GFO) for compositions between
0.8 <= x <= 1.3. X-ray analysis reveals that lattice parameters of GFO exhibit
a linear dependence on Fe content in single phase region indicating
manifestation of Vegard's law. Increasing Fe content of the samples also leads
to stretching of bonds as indicated by the Raman peak shifts. Further, low
temperature magnetic measurements show that the coercivity of the samples is
maximum for Ga:Fe ratio of 1:1 driven by a competition between decreasing
crystallite size and increasing magnetic anisotropy.",1107.3623v1
2011-12-15,On the Angular Width of Diffractive Beam in Anisotropic Media,"2-D diffraction patterns arising in the far-field region were investigated
theoretically for the case, when the plane wave with non collinear group and
phase velocities is incident on the wide slit in opaque screen with arbitrary
orientation. This investigation was carried out by consideration as an example
of magnetostatic surface wave diffraction in tangentially magnetized ferrite
slab. It was deduced the universal analytical formula, which one can use to
calculate the angular width of diffractive beam in any 2-D anisotropic
geometries for the waves of various nature. It was shown, that in 2-D
anisotropic geometries this width may be not only more or less then the value
L/D (L - wavelength of incident wave, D - length of slit), but it also may be
equal to zero in certain conditions.",1112.3929v1
2012-02-06,High-temperature spin-wave propagation in BiFeO3: relation to the Polomska transition,"In bismuth ferrite thin films the cycloidal spiral spin structure is
suppressed, and as a result the spin-wave magnon branches of long wavelength
are reduced from a dozen to one, at \omega = 19.2 cm-1 (T=4K). This spin wave
has not been measured previously above room temperature, but in the present
work we show via Raman spectroscopy that it is an underdamped propagating wave
until 455 K. This has important room-temperature device implications. The data
show that \omega(T) follows an S=5/2 Brillouin function and hence its Fe+3 ions
are in the high-spin 5/2 state and not the low-spin S=1/2 state. The spin wave
cannot be measured as a propagating wave above 455 K. We also suggest that
since this temperature is coincident with the mysterious ""Polomska transition""
(M. Polomska et al., Phys. Stat. Sol. A 23, 567, (1974)) at 458+/-5 K, that
this may be due to overdamping.",1202.1040v1
2012-02-15,Surface phase transitions in BiFeO3 below room temperature,"We combine a wide variety of experimental techniques to analyze two
heretofore mysterious phase transitions in multiferroic bismuth ferrite at low
temperature. Raman spectroscopy, resonant ultrasound spectroscopy, EPR, X-ray
lattice constant measurements, conductivity and dielectric response, specific
heat and pyroelectric data have been collected for two different types of
samples: single crystals and, in order to maximize surface/volume ratio to
enhance surface phase transition effects, BiFeO3 nanotubes were also studied.
The transition at T=140.3K is shown to be a surface phase transition, with an
associated sharp change in lattice parameter and charge density at the surface.
Meanwhile, the 201K anomaly appears to signal the onset of glassy behaviour.",1202.3387v1
2012-02-19,"Nanoscale austenite reversion through partitioning, segregation, and kinetic freezing: Example of a ductile 2 GPa Fe-Cr-C steel","Austenite reversion during tempering of a Fe-13.6Cr-0.44C (wt.%) martensite
results in an ultrahigh strength ferritic stainless steel with excellent
ductility. The austenite reversion mechanism is coupled to the kinetic freezing
of carbon during low-temperature partitioning at the interfaces between
martensite and retained austenite and to carbon segregation at
martensite-martensite grain boundaries. An advantage of austenite reversion is
its scalability, i.e., changing tempering time and temperature tailors the
desired strength-ductility profiles (e.g. tempering at 400{\deg}C for 1 min.
produces a 2 GPa ultimate tensile strength (UTS) and 14% elongation while 30
min. at 400{\deg}C results in a UTS of ~ 1.75 GPa with an elongation of 23%).
The austenite reversion process, carbide precipitation, and carbon segregation
have been characterized by XRD, EBSD, TEM, and atom probe tomography (APT) in
order to develop the structure-property relationships that control the
material's strength and ductility.",1202.4135v1
2012-02-28,"Gallium Substituted ""114"" YBaFe4O7: From a ferrimagnetic cluster glass to a cationic disordered spin glass","The study of the ferrites YBaFe4-xGaxO7 shows that the substitution of Ga for
Fe in YBaFe4O7 stabilizes the hexagonal symmetry for 0.40 < x < 0.70, at the
expense of the cubic one. Using combined measurements of a. c. and d. c.
magnetization, we establish that Ga substitution for Fe in YBaFe4O7 leads to an
evolution from a geometrically frustrated spin glass (for x = 0) to a cationic
disorder induced spin glass (x = 0.70). We also find an intermediate narrow
range of doping where the samples are clearly phase separated having small
ferrimagnetic clusters embedded in a spin glass matrix. The origin of the
ferrimagnetic clusters lies in the change in symmetry of the samples from cubic
to hexagonal (and a consequent lifting of the geometrical frustration) as a
result of Ga doping. We also show the presence of exchange bias and domain wall
pinning in these samples. The cause of both these effects can be traced back to
the inherent phase separation present in the samples.",1202.6166v1
2012-07-19,Raman study of the phonon symmetries in BiFeO$_3$ single crystals,"In bismuth ferrite (BiFeO3), antiferromagnetic and ferroelectric order
coexist at room temperature, making it of particular interest for studying
magnetoelectric coupling. The mutual control of magnetic and electric
properties is very useful for a wide variety of applications. This has led to
an enormous amount of research into the properties of BiFeO$_3$. Nonetheless,
one of the most fundamental aspects of this material, namely the symmetries of
the lattice vibrations, remains controversial.We present a comprehensive Raman
study of BiFeO$_3$ single crystals with the approach of monitoring the Raman
spectra while rotating the polarization direction of the excitation laser. Our
method results in unambiguous assignment of the phonon symmetries and explains
the origin of the controversy in the literature. Furthermore, it provides
access to the Raman tensor elements enabling direct comparison with theoretical
calculations. Hence, this allows the study of symmetry breaking and coupling
mechanisms in a wide range of complex materials and may lead to a noninvasive,
all-optical method to determine the orientation and magnitude of the
ferroelectric polarization.",1207.4799v1
2012-10-03,Direct calorimetric measurements of isothermal entropy change on single crystal W-type hexaferrites at the spin reorientation transition,"We report on the magnetic field induced isothermal entropy change, \Delta
s(Ha, T), of W-type ferrite with CoZn substitution. Entropy measurements are
performed by direct calorimetry. Single crystals of the composition
BaCo$_0.62$Zn$_1.38$Fe$_16$O$_27$, prepared by the flux method, are measured at
different fixed temperatures under an applied field perpendicular and parallel
to the c axis. At 296 K one deduces a value of K$_1$ = 8.7 \times 10^{4} J
m$^-3$ for the first anisotropy constant, which is in good agreement with the
literature. The spin reorientation transition temperature is estimated to take
place between 200 and 220 K.",1210.0997v1
2012-11-05,Exact asymptotic behavior of magnetic stripe domain arrays,"The classical problem of magnetic stripe domain behavior in films and plates
with uniaxial magnetic anisotropy is treated. Exact analytical results are
derived for the stripe domain widths as function of applied perpendicular
field, $H$, in the regime where the domain period becomes large. The stripe
period diverges as $(H_c-H)^{-1/2}$, where $H_c$ is the critical (infinite
period) field, an exact result confirming a previous conjecture. The
magnetization approaches saturation as $(H_c-H)^{1/2}$, a behavior which
compares excellently with experimental data obtained for a $4 \mu$m thick
ferrite garnet film. The exact analytical solution provides a new basis for
precise characterization of uniaxial magnetic films and plates, illustrated by
a simple way to measure the domain wall energy. The mathematical approach is
applicable for similar analysis of a wide class of systems with competing
interactions where a stripe domain phase is formed.",1211.1366v1
2013-01-11,Spin-filtering efficiency of ferrimagnetic spinels CoFe2O4 and NiFe2O4,"We assess the potential of the ferrimagnetic spinel ferrites CoFe2O4 and
NiFe2O4 to act as spin filtering barriers in magnetic tunnel junctions. Our
study is based on the electronic structure calculated by means of
first-principles density functional theory within different approximations for
the exchange correlation energy. We show that, in agreement with previous
calculations, the densities of states suggest a lower tunneling barrier for
minority spin electrons, and thus a negative spin-filter effect. However, a
more detailed analysis based on the complex band-structure reveals that both
signs for the spin-filtering efficiency are possible, depending on the band
alignment between the electrode and the barrier materials and depending on the
specific wave-function symmetry of the relevant bands within the electrode.",1301.2541v1
2013-02-12,Anomalous Surface Segregation Profiles in Ferritic FeCr Stainless Steel,"The iron-chromium alloy and its derivatives are widely used for their
remarkable resistance to corrosion, which only occurs in a narrow concentration
range around 9 to 13 atomic percent chromium. Although known to be due to
chromium enrichment of a few atoms thick layer at the surfaces, the
understanding of its complex atomistic origin has been a remaining challenge.
We report an investigation of the thermodynamics of such surfaces at the atomic
scale by means of Monte Carlo simulations. We use a Hamiltonian which provides
a parameterization of previous ab initio results and successfully describes the
alloy's unusual thermodynamics. We report a strong enrichment in Cr of the
surfaces for low bulk concentrations, with a narrow optimum around 12 atomic
percent chromium, beyond which the surface composition decreases drastically.
This behavior is explained by a synergy between (i) the complex phase
separation in the bulk alloy, (ii) local phase transitions that tune the layers
closest to the surface to an iron-rich state and inhibit the bulk phase
separation in this region, and (iii) its compensation by a strong and
non-linear enrichment in Cr of the next few layers. Implications with respect
to the design of prospective nanomaterials are briefly discussed.",1302.2838v1
2013-02-16,Room Temperature Nanoscale Ferroelectricity in Magnetoelectric GaFeO3 Epitaxial Thin Films,"We demonstrate room temperature ferroelectricity in the epitaxial thin films
of magnetoelectric GaFeO3. Piezo-force measurements show a 180o phase shift of
piezoresponse upon switching the electric field indicating nanoscale
ferroelectricity in epitaxial thin films of gallium ferrite. Further,
temperature dependent impedance analysis with and without the presence of an
external magnetic field clearly reveals a pronounced magneto-dielectric effect
across the magnetic transition temperature. In addition, our first principles
calculations show that Fe ions are not only responsible for ferrimagnetism as
observed earlier, but also give rise to the observed ferroelectricity, making
GFO an unique single phase multiferroic.",1302.3983v2
2013-04-04,Surface parameters of ferritic iron-rich Fe-Cr alloy,"Using first-principles density functional theory in the implementation of the
exact muffin-tin orbitals method and the coherent potential approximation, we
studied the surface energy and the surface stress of the thermodynamically most
stable surface facet (100) of the homogeneous disordered body-centred cubic
iron-chromium system in the concentration interval up to 20 at.% Cr. For the
low-index surface facets of Fe and Cr, the surface energy of Cr is slightly
larger than the one of Fe, while the surface stress of Cr is considerably
smaller than the one of Fe. We find that Cr addition to Fe generally increases
the surface energy of the Fe-Cr alloy, however, an increase of the bulk amount
of Cr also increases the surface stress. As a result of this unexpected trend,
the (100) surface of Fe-Cr becomes more stable against reconstruction with
increasing Cr concentration. We show that the observed trends are of magnetic
origin. In addition to the homogeneous alloy case, we also investigated the
impact of surface segregation on both surface parameters.",1304.1278v2
2013-07-29,Simple concentration-dependent pair interaction model for large-scale simulations of Fe-Cr alloys,"This work is motivated by the need for large-scale simulations to extract
physical information on the iron-chromium system that is a binary model alloy
for ferritic steels used or proposed in many nuclear applications. From
first-principles calculations and the experimental critical temperature we
build a new energetic rigid lattice model based on pair interactions with
concentration and temperature dependence. Density functional theory
calculations in both norm-conserving and projector augmented-wave approaches
have been performed. A thorough comparison of these two different ab initio
techniques leads to a robust parametrization of the Fe-Cr Hamiltonian.
Mean-field approximations and Monte Carlo calculations are then used to account
for temperature effects. The predictions of the model are in agreement with the
most recent phase diagram at all temperatures and compositions. The solubility
of Cr in Fe below 700 K remains in the range of about 6 to 12%. It reproduces
the transition between the ordering and demixing tendency and the spinodal
decomposition limits are also in agreement with the values given in the
literature.",1307.7561v1
2013-11-05,"Diffusion behavior in diluted ($Fe,Cr$) alloys: An environment for H diffusion in ferritic steels","Impurity diffusion coefficients are entirely obtained from a low cost
classical molecular statics technique (CMST). In particular, we show how the
CMST is appropriate in order to describe the impurity diffusion behavior
mediated by a vacancy mechanism. In the context of the five-frequency model,
CMST allows to calculate all the microscopic parameters, namely: the free
energy of vacancy formation, the vacancy-solute binding energy and the involved
jump frequencies, from them, we obtain the macroscopic transport magnitudes
such as: correlation factor, solvent-enhancement factor, Onsager and diffusion
coefficients. Also, we report for the first time the behavior of diffusion
coefficients for the solute-vacancy paired specie. We perform our calculations
in diluted NiAl and AlU f.c.c. alloys. Our results are in perfect agreement
with available experimental data for both systems and predict that for NiAl the
solute diffuses through a vacancy interchange mechanism, while for the AlU
system, a vacancy drag mechanism occurs.",1311.1177v1
2013-12-09,Giant Photogalvanic Effect in Metamaterials Containing Non-Centrosymmetric Plasmonic Nanoparticles,"Photoelectric properties of metamaterials containing non-centrosymmetric,
similarly oriented metallic nanoparticles embedded in a homogeneous
semiconductor matrix are theoretically studied. Due to the asymmetric shape of
the nanoparticle boundary, photoelectron emission acquires a preferred
direction, resulting in a photocurrent flow in that direction when
nanoparticles are uniformly illuminated by a homogeneous plane wave. This
effect is a direct analogy of the photogalvanic (or bulk photovoltaic) effect
known to exist in media with non-centrosymmetric crystal structure, such as
doped lithium niobate or bismuth ferrite, but is several orders of magnitude
stronger. Termed the giant plasmonic photogalvanic effect, the reported
phenomenon is valuable for characterizing photoemission and photoconductive
properties of plasmonic nanostructures, and can find many uses for
photodetection and photovoltaic applications.",1312.2428v2
2014-01-20,Determining polarizability tensors for an arbitrary small electromagnetic scatterer,"In this paper, we present a method to retrieve tensor polarizabilities of
general bi-anisotropic particles from their far-field responses to plane-wave
illuminations. The necessary number of probing excitations and the directions
where the scattered fields need to be calculated or measured have been found.
When implemented numerically, the method does not require any spherical
harmonic expansion nor direct calculation of dipole moments, but only
calculations of co- and cross-polarized scattering cross sections for a number
of plane-wave excitations. With this simple approach, the polarizabilities can
be found also from experimentally measured cross sections. The method is
exemplified considering two bi-anisotropic particles, a reciprocal omega
particle and a non-reciprocal particle containing a ferrite inclusion coupled
to metal strips.",1401.4930v1
2014-02-14,Scattering Experiments with Microwave Billiards at an Exceptional Point under Broken Time Reversal Invariance,"Scattering experiments with microwave cavities were performed and the effects
of broken time-reversal invariance (TRI), induced by means of a magnetized
ferrite placed inside the cavity, on an isolated doublet of nearly degenerate
resonances were investigated. All elements of the effective Hamiltonian of this
two-level system were extracted. As a function of two experimental parameters,
the doublet and also the associated eigenvectors could be tuned to coalesce at
a so-called exceptional point (EP). The behavior of the eigenvalues and
eigenvectors when encircling the EP in parameter space was studied, including
the geometric amplitude that builds up in the case of broken TRI. A
one-dimensional subspace of parameters was found where the differences of the
eigenvalues are either real or purely imaginary. There, the Hamiltonians were
found PT-invariant under the combined operation of parity (P) and time reversal
(T) in a generalized sense. The EP is the point of transition between both
regions. There a spontaneous breaking of PT occurs.",1402.3537v1
2014-04-06,Preparation and Characterization of Nano-particle Substituted Barium Hexaferrite,"High density magnetic recording requires high coercivity magnetic media and
small particle size. Barium hexaferrite has been considered as a leading
candidate material because of its chemical stability, fairly large crystal
anisotropy and suitable magnetic characteristics. In this work, we present the
preparation of the hexagonal ferrite BaFe12O19 and one of its derivative; the
Zn-Sn substituted hexaferrite by the chemical co-precipitation method. The main
advantage of this method on the conventional glass-ceramic one, resides in
providing a small enough particle size for magnetic recording. We demonstrate
using the X-ray diffraction patterns that the particle size decreases when
substituting the hexaferrite by the Zn-Sn combination. This may improve the
magnetic properties of the hexaferrite as a medium for HD magnetic recording",1404.1573v1
2014-04-22,"Analytic Modeling, Simulation and Interpretation of Broadband Beam Coupling Impedance Bench Measurements","In the first part of the paper a generalized theoretical approach towards
beam coupling impedances and stretched-wire measurements is introduced. Applied
to a circular symmetric setup, this approach allows to estimate the systematic
measurement error due to the presence of the wire. Further, the interaction of
the beam or the TEM wave, respectively, with dispersive material such as
ferrite is discussed. The dependence of the obtained impedances on the
relativistic velocity $\beta$ is investigated and found as material property
dependent. The conversion formulas for the TEM scattering parameters from
measurements to impedances are compared with each other and the analytical
impedance solution. In the second part of the paper the measurements are
compared to numerical simulations of wakefields and scattering parameters. In
practice, the measurements have been performed for the circularly symmetric
example setup. The optimization of the measurement process is discussed. The
paper concludes with a summary of systematic and statistic error sources for
impedance bench measurements and their diminishment strategy.",1404.5593v1
2014-07-21,Unidirectional magnetoelectric-field multiresonant tunneling,"Unidirectional multi-resonant tunneling of the magneto-electric (ME)-field
excitations through a sub wavelength (regarding the scales of regular
electromagnetic radiation) vacuum or isotropic-dielectric regions has been
observed in two-port microwave structures having a quasi-2D ferrite disk with
magnetic-dipolar-mode (MDM) oscillations. The excitations manifest themselves
as the Fano-resonance peaks in the scattering-matrix parameters at the
stationary states of the MDM spectrum. The ME near-field excitations are quasi
magnetostatic fields with non-zero helicity parameter. Topological-phase
properties of ME fields are determined by edge chiral currents of MDM
oscillations. We show that while for a given direction of a bias magnetic field
(in other words, for a given direction of time), the ME-field excitations are
considered as forward tunneling processes, in the opposite direction of a bias
magnetic field (the opposite direction of time), there are backward tunneling
processes. Unidirectional ME-field resonant tunneling is observed due to
distinguishable topology of the forward and backward ME-field excitations. We
establish a close connection between the Fano-resonance unidirectional
tunneling and topology of ME fields in different microwave structures.",1407.5522v1
2014-08-01,Effect of the techniqie of drawing with shear on the structure and the properties of low-carbon wires,"The technology of drawing with shear is developed. It allows increasing
technological plasticity of low carbon steel without heat treatment. It is
found that the use of experimental technology can improve mechanical properties
of wire samples with the diameter reduced during drawing: the relative
reduction of the wire decreases slightly and remains at high level compared
with the classical technology, where the relative reduction in the course of
drawing drops more than twice. It is shown that the use of experimental
technology allows varying the size of a ferrite grain (increase or decrease)
compared with the classical technology, where increasing of deformation degree
results in grain reduction. Furthermore, the experimental technology allows
reducing the number of pores in a wire of small diameter. To prevent heating of
the wire and the drawing dies, it is proposed to use experimental drawing
through two experimental dies with shear separated by an ordinary die. As a
result, the workability of the process will be enhanced and the efforts of
drawing will be reduced.",1408.0125v1
2014-08-07,Deviations from cooperative growth mode during eutectoid transformation: insights from phase-field approach,"The non-cooperative eutectoid transformation relies on the presence of
pre-existing cementite particles in the parent austenitic phase and yields a
product, popularly known as the divorced eutectoid. In isothermal conditions,
two of the important parameters, which influence the transformation mechanism
and determine the final morphology are undercooling (below A1 temperature) and
inter-particle spacing. Although, the criteria which governs the morphological
transition from lamellar to divorced is experimentally well established,
numerical studies that give a detailed exposition of the non-cooperative
transformation mechanism, have not been reported extensively. In the present
work, we employ a multiphase-field model, that uses the thermodynamic
information from the CALPHAD database, to numerically simulate the pulling-away
of the advancing ferrite-austenite interface from cementite, which results in a
transition from lamellar to divorced eutectoid morphology in Fe-C alloy. We
also identify the onset of a concurrent growth and coarsening regime at small
inter-particle spacing and low undercooling. We analyze the simulation results
to unravel the essential physics behind this complex spacial and temporal
evolution pathway and amend the existing criteria by constructing a
Lamellar-Divorced-Coarsening (LDC) map.",1408.1571v1
2014-08-14,Role of magnetic degrees of freedom in a scenario of phase transformations in steel,"The diversity of mesostructures formed in steel at cooling from a
high-temperature austenite (""gamma"") phase is determined by the interplay of
shear reconstructions of crystal lattice and diffusion of carbon. Combining
first-principles calculations with large-scale phase-field simulations we
demonstrate a decisive role of magnetic degrees of freedom in the formation of
energy relief along the Bain path of ""gamma""-""alpha"" transformation and, thus,
in this interplay. We show that there is the main factor, namely, the magnetic
state of iron and its evolution with temperature which controls the change in
character of the transformation. Based on the computational results we propose
a simple model which reproduces, in good agreement with experiment, the most
important curves of the phase transformation in Fe-C, namely, the lines
relevant to a start of ferrite, bainite, and martensite transformations.
Phase-field simulations within the model describe qualitatively typical
patterns at these transformations.",1408.3275v2
2014-09-05,Theoretical assessment of boron incorporation in nickel ferrite under conditions of operating nuclear pressurized water reactors (PWRs),"A serious concern in the safety and economy of a pressurized water nuclear
reactor is related to the accumulation of boron inside the metal oxide (mostly
NiFe${}_{2}$O${}_{4}$ spinel) deposits on the upper regions of the fuel rods.
Boron, being a potent neutron absorber, can alter the neutron flux causing
anomalous shifts and fluctuations in the power output of the reactor core. This
phenomenon reduces the operational flexibility of the plant and may force the
down-rating of the reactor. In this work an innovative approach is used to
combine first-principles calculations with thermodynamic data to evaluate the
possibility of B incorporation into the crystal structure of
NiFe${}_{2}$O${}_{4}$, under conditions typical to operating nuclear
pressurized water nuclear reactors. Analyses of temperature and pH dependence
of the defect formation energies indicate that B can accumulate in
NiFe${}_{2}$O${}_{4}$ as an interstitial impurity and may therefore be a major
contributor to the anomalous axial power shift observed in nuclear reactors.
This computational approach is quite general and applicable to a large variety
of solids in equilibrium with aqueous solutions.",1409.1811v1
2014-10-29,Simultaneous Multi-Harmonic Imaging of Nanoparticles in Tissues for Increased Selectivity,"We investigate the use of Bismuth Ferrite (BFO) nanoparticles for tumor
tissue labelling in combination with infrared multi-photon excitation at 1250
nm. We report the efficient and simultaneous generation of second and third
harmonic by the nanoparticles. On this basis, we set up a novel imaging
protocol based on the co-localization of the two harmonic signals and
demonstrate its benefits in terms of increased selectivity against endogenous
background sources in tissue samples. Finally, we discuss the use of BFO
nanoparticles as mapping reference structures for correlative light-electron
microscopy.",1410.7969v2
2014-11-09,Gaussian Beam Transmission through a Gyrotropic-Nihility Finely-Stratified Structure,"The three-dimensional Gaussian beam transmission through a
ferrite-semiconductor finely-stratified structure being under an action of an
external static magnetic field in the Faraday geometry is considered. The beam
field is represented by an angular continuous spectrum of plane waves. In the
long-wavelength limit, the studied structure is described as a
gyroelectromagnetic medium defined by the effective permittivity and effective
permeability tensors. The investigations are carried out in the frequency band
where the real parts of the on-diagonal elements of both effective permittivity
and effective permeability tensors are close to zero while the off-diagonal
ones are non-zero. In this frequency band the studied structure is referred to
a gyrotropic-nihility medium. It is found out that a Gaussian beam keeps its
parameters unchanged (beam width and shape) when passing through the layer of
such a medium except of a portion of the absorbed energy.",1411.2233v2
2015-02-01,Magnetoelectric-field helicities and reactive power flows,"The dual symmetry between the electric and magnetic fields underlies
Maxwell's electrodynamics. Due to this symmetry one can describe topological
properties of an electromagnetic field in free space and obtain the
conservation law of optical (electromagnetic) helicity. What kind of the field
helicity one can expect to see when the electromagnetic-field symmetry is
broken? The near fields originated from small ferrite particles with magnetic
dipolar mode (MDM) oscillations are the fields with the electric and magnetic
components, but with broken dual (electric-magnetic) symmetry. These fields,
called magnetoelectric (ME) fields, have topological properties different from
such properties of electromagnetic fields. The helicity states of ME fields are
topologically protected quantum like states. In this paper, we study the
helicity properties of ME fields. We analyze conservation laws of the ME-field
helicity and show that the helicity density is related to an imaginary part of
the complex power flow density. We show also that the helicity of ME fields can
be a complex value.",1502.00220v1
2015-02-04,"Novel microwave near-field sensors for material characterization, biology, and nanotechnology","The wide range of interesting electromagnetic behavior of contemporary
materials requires that experimentalists working in this field master many
diverse measurement techniques and have a broad understanding of condensed
matter physics and biophysics. Measurement of the electromagnetic response of
materials at microwave frequencies is important for both fundamental and
practical reasons. In this paper, we propose a novel near-field microwave
sensor with application to material characterization, biology, and
nanotechnology. The sensor is based on a subwavelength ferrite-disk resonator
with magnetic-dipolar-mode (MDM) oscillations. Strong energy concentration and
unique topological structures of the near fields originated from the MDM
resonators allow effective measuring material parameters in microwaves, both
for ordinary structures and objects with chiral properties.",1502.01121v1
2015-03-25,Study of helium irradiation induced hardening in MNHS steel,"A recently developed reduced activation ferritic/martensitic steel MNHS was
irradiated with 200keV He ions to a fluence of 1E21ions/m^2 at 450 celsius
degree and 1E20ions/m^2 at 300 celsius degree and 450 celsius degree,
respectively. The irradiation hardening of the steel was investigated by
nanoindentation measurements combined with transmission electron microscopy
(TEM) analysis. Dispersed barrier-hardening (DBH) model was applied to predict
the hardness increments based on TEM analysis. The predicted hardness
increments are consistent with the values obtained by nanoindentation tests. It
is found that dislocation loops and He bubbles are hard barriers against
dislocation motion and they are the main contributions to He
irradiation-induced hardening of MNHS steel. The obstacle strength of He
bubbles is stronger than the obstacle strength of dislocation loops.",1503.08088v1
2015-04-07,Impedance Measurements of the Extraction Kicker System for the Rapid Cycling Synchrotron of China Spallation Neutron Source,"The fast extraction kicker system is one of the most important accelerator
components, whose inner structure will be the main source of the impedance in
the RCS. It is necessary to understand the kicker impedance before its
installation into the tunnel. The conventional and improved wire methods are
employed for the benchmarking impedance measurement results. The simulation and
measurements confirm that the window-frame ferrite geometry and the end plate
are the important structures causing the coupling impedance. The total
impedance of the eight modules systems is determined by the scaling law from
the measurement and the impedance measurement of the kicker system is
summarized.",1504.01500v1
2015-04-15,Acoustic study for dynamical molecular-spin state without undergoing magnetic phase transition in spin-frustrated ZnFe$_2$O$_4$,"Ultrasound velocity measurements were performed on a single crystal of
spin-frustrated ferrite spinel ZnFe$_2$O$_4$ from 300 K down to 2 K. In this
cubic crystal, all the symmetrically-independent elastic moduli exhibit
softening with a characteristic minimum with decreasing temperature below
$\sim$100 K. This elastic anomaly suggests a coupling between dynamical lattice
deformations and molecular-spin excitations. In contrast, the elastic
anomalies, normally driven by the magnetostructural phase transition and its
precursor, are absent in ZnFe$_2$O$_4$, suggesting that the spin-lattice
coupling cannot play a role in relieving frustration within this compound. The
present study infers that, for ZnFe$_2$O$_4$, the dynamical molecular-spin
state evolves at low temperatures without undergoing precursor spin-lattice
fluctuations and spin-lattice ordering. It is expected that ZnFe$_2$O$_4$
provides the unique dynamical spin-lattice liquid-like system, where not only
the spin molecules but also the cubic lattice fluctuate spatially and
temporally.",1504.03792v3
2015-05-15,Linear roto-antiferromagnetic effect in multiferroics: physical manifestations,"Using the theory of symmetry and the microscopic model we predicted the
possibility of a linear roto-antiferromagnetic effect in the perovskites with
structural antiferrodistortive and antiferromagnetic long-range ordering and
found the necessary conditions of its occurrence. The main physical
manifestations of this effect are the smearing of the antiferromagnetic
transition and the jump of the specific heat near it. In the absence of
external fields linear roto-antiferromagnetic coupling can induce a weak
antiferromagnetic ordering above the Neel temperature, but below the
temperature of antiferrodistortive transition. Therefore, there is the
possibility of observing weak antiferromagnetism in multiferroics such as
bismuth ferrite (BiFeO3) at temperatures T>TN, for which the Neel temperature
TN is about 645 K, and the antiferrodistortive transition temperature is about
1200 K. By quantitative comparison with experiment we made estimations of the
linear roto-antiferromagnetic effect in the solid solutions of multiferroic
Bi1-xRxFeO3 (R=La, Nd).",1505.04136v1
2015-05-24,"Structural Properties, Impedance Spectroscopy and Dielectric Spin Relaxation of Ni-Zn Ferrite Synthesized by Double Sintering Technique","Structural properties, impedance, dielectric and electric modulus spectra
have been used to investigate the sintering temperature (Ts) effect on the
single phase cubic spinel Ni0.6Zn0.4Fe2O4 (NZFO) ceramics synthesized by
standard ceramic technique. Enhancement of dielectric constants is observed
with increasing Ts. The collective contribution of n-type and p-type carriers
yields a clear peak in notable unusual dielectric behavior is successfully
explained by the Rezlescu model. The non-Debye type long range dielectric
relaxation phenomena is explained by electric modulus formalism. Fast response
of the grain boundaries of the sample sintered at lower Ts sample leading to
small dielectric spin relaxation time, t (several nanoseconds) have been
determined using electric modulus spectra for the samples sintered at different
Ts. Two clear semicircles in impedance Cole-Cole plot have also been
successfully explained by employing two parallel RC equivalent circuits in
series configuration taking into account no electrode contribution. Such a long
relaxation time in NZFO ceramics could suitably be used in nanoscale spintronic
devices.",1505.06438v2
2015-06-01,Calculating the 3D magnetic field of ITER for European TBM studies,"The magnetic perturbation due to the ferromagnetic test blanket modules
(TBMs) may deteriorate fast ion confinement in ITER. This effect must be
quantified by numerical studies in 3D. We have implemented a combined finite
element method (FEM) -- Biot-Savart law integrator method (BSLIM) to calculate
the ITER 3D magnetic field and vector potential in detail. Unavoidable geometry
simplifications changed the mass of the TBMs and ferritic inserts (FIs) up to
26%. This has been compensated for by modifying the nonlinear ferromagnetic
material properties accordingly. Despite the simplifications, the computation
geometry and the calculated fields are highly detailed. The combination of
careful FEM mesh design and using BSLIM enables the use of the fields
unsmoothed for particle orbit-following simulations. The magnetic field was
found to agree with earlier calculations and revealed finer details. The vector
potential is intended to serve as input for plasma shielding calculations.",1506.00659v1
2015-06-16,Parametric excitation of surface magnetostatic modes in an axially magnetized elliptic cylinder under longitudinal pumping,"A rigorous analytical theory of parametric excitation under the longitudinal
pumping has been developed for the surface magnetostatic modes of a long
elliptic ferrite cylinder magnetized along its axis with regard for the
boundary conditions at the surface of the cylinder.It is shown that a pair of
frequency-degenerated counter-propagating surface modes at half the pumping
frequency can be parametrically excited, and the expressions for the
corresponding parametric excitation threshold have been derived. The threshold
demonstrates a strong dependence on the mode number and elliptic cylinder's
aspect ratio and tends from above for the large aspect ratio to the value
deduced on the basis of the plane-wave analysis.The simple analytical relation
between the ratio of axes of the high-frequency magnetization polarization
ellipse of excited surface magnetostatic oscillations and the parametric
excitation threshold is obtained, discussed, and graphically illustrated.",1506.04968v1
2015-07-07,Fast and rewritable colloidal assembly via field synchronized particle swapping,"We report a technique to realize reconfigurable colloidal crystals by using
the controlled motion of particle defects above an externally modulated
magnetic substrate. The transport of particles is induced by applying a uniform
rotating magnetic field to a ferrite garnet film characterized by a periodic
lattice of magnetic bubbles. For filling factor larger than one colloid per
bubble domain, the particle current arises from propagating defects where
particles synchronously exchange their position when passing from one occupied
domain to the next. The amplitude of an applied alternating magnetic field can
be used to displace the excess particles via a swapping mechanism, or to
mobilize the entire colloidal system at a predefined speed.",1507.01964v1
2015-08-24,First-principles materials design of high-performing bulk photovoltaics with the LiNbO$_3$ structure,"The bulk photovoltaic effect is a long-known but poorly understood
phenomenon. Recently, however, the multiferroic bismuth ferrite has been
observed to produce strong photovoltaic response to visible light, suggesting
that the effect has been underexploited as well. Here we present three polar
oxides in the LiNbO$_3$ structure that we predict to have band gaps in the 1-2
eV range and very high bulk photovoltaic response: PbNiO$_3$,
Mg$_{1/2}$Zn$_{1/2}$PbO$_3$, and LiBiO$_3$. All three have band gaps determined
by cations with $d^{10}s^0$ electronic configurations, leading to conduction
bands composed of cation $s$-orbitals and O $p$-orbitals. This both
dramatically lowers the band gap and increases the bulk photovoltaic response
by as much as an order of magnitude over previous materials, demonstrating the
potential for high-performing bulk photovoltaics.",1508.05874v1
2015-10-19,Ferroelectric polarization switching with a remarkably high activation-energy in orthorhombic GaFeO3 thin films,"Orthorhombic GaFeO3 (o-GFO) with the polar Pna21 space group is a prominent
ferrite by virtue of its piezoelectricity and ferrimagnetism, coupled with
magneto-electric effects. Herein, we unequivocally demonstrate a large
ferroelectric remanent polarization in undoped o-GFO thin films by adopting
either a hexagonal strontium titanate (STO) or a cubic yttrium-stabilized
zirconia (YSZ) substrate. The polarization-electric-field hysteresis curves of
the polar c-axis-grown o-GFO film on a SrTiO3/STO substrate show the net
switching polarization of ~35 {\mu}C/cm2 with an unusually high coercive field
of +-1400 kV/cm at room temperature. The PUND measurement also demonstrates the
switching polarization of ~26 {\mu}C/cm2. The activation energy for the
polarization switching, as obtained by density-functional theory calculations,
is remarkably high, 1.05 eV per formula unit. This high value accounts for the
observed stability of the polar Pna21 phase over a wide range of temperature up
to 1368 K.",1510.05359v1
2015-11-24,In situ resonant photoemission and X-ray absorption study of the BiFeO3 thin film,"Multiferroic bismuth ferrite (BiFeO3) thin films were prepared by pulsed
laser deposition (PLD) technique. Electronic structures of the film have been
studied by in situ photoemission spectroscopy (PES) and x-ray absorption
spectroscopy (XAS). Both the Fe 2p PES and XAS spectra show that Fe ion is
formally in +3 valence state. The Fe 2p and O K edge XAS spectra indicate that
the oxygen octahedral crystal ligand field splits the unoccupied Fe 3d state to
t2g and eg states. Valence band Fe 2p-3d resonant photoemission results
indicate that hybridization between Fe 3d and O 2p plays important role in the
multiferroic BiFeO3 thin films.",1511.07747v1
2016-02-19,Study of Aqueous Dispersions of Magnetic Nanoparticles by Magnetic and Rheological Measurements,"The observed magnetic tunability of light transmission through a ferrofluid
can be effectively understood in terms of the inter-particle interaction that
can be estimated from the magnetic and rheological properties of these fluids.
The present study reports complementary magnetic and rheological measurements
of aqueous dispersions of ferrite nanoparticles and a commercial ferrofluid.
The room temperature magnetization measured in a SQUID magnetometer up to
fields of 1 to 2 Tesla showed superparamagnetic behaviour of the particles and
the dispersion with the background signal of the liquid showing a diamagnetic
behaviour. The room temperature rheological behaviour in zero magnetic field of
the fluids was investigated by measuring the viscosity as a function of shear
rate from 1-100 s-1. The particle size and the nature of the carrier liquid
determine the viscosity and is expected to have an effect on the inter-particle
interaction.",1602.06015v1
2016-04-24,Optomagnonics in Magnetic Solids,"Coherent conversion of photons to magnons, and back, provides a natural
mechanism for rapid control of interactions between stationary spins with long
coherence times and high-speed photons. Despite the large frequency difference
between optical photons and magnons, coherent conversion can be achieved
through a three-particle interaction between one magnon and two photons whose
frequency difference is resonant with the magnon frequency, as in optomechanics
with two photons and a phonon. The large spin density of a transparent
ferromagnetic insulator (such as the ferrite yttrium iron garnet) in an optical
cavity provides an intrinsic photon-magnon coupling strength that we calculate
to exceed reported optomechanical couplings. A large cavity photon number and
properly selected cavity detuning produce a predicted effective coupling
strength sufficient for observing electromagnetically induced transparency and
the Purcell effect, and even to reach the ultra-strong coupling regime.",1604.07052v2
2016-06-06,Band gap tuning and orbital mediated electron phonon coupling in $HoFe_{1-x}Cr_xO_3$,"We report on the evidenced orbital mediated electron phonon coupling and band
gap tuning in HoFe1-xCrxO3 compounds. From the room temperature Raman
scattering, it is apparent that the electron-phonon coupling is sensitive to
the presence of both the Fe and Cr at the B-site. Essentially, an Ag like local
oxygen breathing mode is activated due to the charge transfer between Fe3+ -
Cr3+ at around 670 cm-1, this observation is explained on the basis of
Franck-Condon (FC) mechanism. Optical absorption studies infer that there
exists a direct band gap in the HoFe1-xCrxO3 compounds. Decrease in band gap
until x = 0.5 is ascribed to the broadening of the oxygen p orbitals as a
result of the induced spin disorder due to Fe3+ and Cr3+ at B site. In
contrast, the increase in band gap above x = 0.5 is explained on the basis of
the reduction in the available unoccupied d - orbitals of Fe3+ at the
conduction band. We believe that above results would be helpful for the
development of the optoelectronic devices based on the ortho-ferrites.",1606.01698v1
2016-06-18,Magnetization reversal in mixed ferrite-chromite perovskites with non magnetic cation on the A-site,"In this work, we have performed Monte Carlo simulations in a classical model
for RFe$_{1-x}$Cr$_x$O$_3$ with R=Y and Lu, comparing the numerical simulations
with experiments and mean field calculations. In the analyzed compounds, the
antisymmetric exchange or Dzyaloshinskii-Moriya (DM) interaction induced a weak
ferromagnetism due to a canting of the antiferromagnetically ordered spins.
This model is able to reproduce the magnetization reversal (MR) observed
experimentally in a field cooling process for intermediate $x$ values and the
dependence with $x$ of the critical temperatures. We also analyzed the
conditions for the existence of MR in terms of the strength of DM interactions
between Fe$^{3+}$ and Cr$^{3+}$ ions with the x values variations.",1606.05782v1
2016-06-18,Enhanced diffusion and anomalous transport of magnetic colloids driven above a two-state flashing potential,"We combine experiment and theory to investigate the diffusive and
subdiffusive dynamics of paramagnetic colloids driven above a two-state
flashing potential. The magnetic potential was realized by periodically
modulating the stray field of a magnetic bubble lattice in a uniaxial ferrite
garnet film. At large amplitudes of the driving field, the dynamics of
particles resembles an ordinary random walk with a frequency-dependent
diffusion coefficient. However, subdiffusive and oscillatory dynamics at short
time scales is observed when decreasing the amplitude. We present a persistent
random walk model to elucidate the underlying mechanism of motion, and perform
numerical simulations to demonstrate that the anomalous motion originates from
the dynamic disorder in the structure of the magnetic lattice, induced by
slightly irregular shape of bubbles.",1606.05783v1
2016-07-19,Synthesis of strontium ferrite/iron oxide exchange coupled nano-powders with improved energy product for rare earth free permanent magnet applications,"We present a simple, scalable synthesis route for producing exchange coupled
soft/hard magnetic composite powder that outperforms pure soft and hard phase
constituents. Importantly, the composites is iron oxide based (SrFe12O19 and
Fe3O4) and contain no rare earth or precious metal. The two step synthesis
process consists of first precipitating, an Iron oxide/hydroxide precursor
directly on top of SrFe12O19 nano-flakes, ensuring a very fine degree of mixing
between the hard and the soft magnetic phases. We then use a second step that
serves to reduce the precursor to create the proper soft magnetic phase and
create the intimate interface necessary for exchange coupling. We establish a
clear processing window; at temperatures below this window the desired soft
phase is not produced, while higher temperatures result in deleterious reaction
at the soft/hard phase interfaces, causing an improper ratio of soft to hard
phases. Improvements of Mr, Ms, and (BH)max are 42%, 29% and 37% respectively
in the SrFe12O19/Fe3O4 composite compared to pure hard phase (SrFe12O19). We
provide evidence of coupling (exchange spring behavior) with hysteresis curves,
first order reversal curve (FORC) analysis and recoil measurements.",1607.05689v1
2016-09-14,Piezo-generated charge mapping revealed through Direct Piezoelectric Force Microscopy,"While piezoelectrics and ferroelectrics are playing a key role in many
everyday applications, there are still a number of open questions related to
the physics of those materials. In order to foster the understanding of
piezoelectrics and ferroelectric and pave the way to future applications, the
nanoscale characterization of these materials is essential. In this light, we
have developed a novel AFM based mode that obtains a direct quantitative
analysis of the piezoelectric coefficient d33. This nanoscale tool is capable
of detecting and reveal piezo-charge generation through the direct
piezoelectric effect at the surface of the piezoelectric and ferroelectric
materials. We report the first nanoscale images of the charge generated in a
thick single crystal of Periodically Poled Lithium Niobate (PPLN) and a Bismuth
Ferrite (BiFO3) thin film by applying a force and recording the current
produced by the materials. The quantification of both d33 coefficients for PPLN
and BFO are 13 +- 2 pC/N and 46 +- 7 pC/N respectively, in agreement with the
values reported in the literature. This new mode can operate simultaneously
with PFM mode providing a powerful tool for the electromechanical and
piezo-charge generation characterization of ferroelectric and piezoelectric
materials.",1609.04250v1
2016-10-14,Bidirectional particle transport and size selective sorting of Brownian particles in a flashing spatially periodic energy landscape,"We demonstrate a size sensitive experimental scheme which enables
bidirectional transport and fractionation of paramagnetic colloids in a fluid
medium. It is shown that two types of magnetic colloidal particles with
different sizes can be simultaneously transported in opposite directions, when
deposited above a stripe-patterned ferrite garnet film subjected to a
square-wave magnetic modulation. Due to their different sizes, the particles
are located at distinct elevations above the surface, and they experience two
different energy landscapes, generated by the modulated magnetic substrate. By
combining theoretical arguments and numerical simulations, we reveal such
energy landscapes, which fully explain the bidirectional transport mechanism.
The proposed technique does not require pre-imposed channel geometries such as
in conventional microfluidics or lab-on-a-chip systems, and permits remote
control over the particle motion, speed and trajectory, by using relatively low
intense magnetic fields.",1610.04380v1
2016-10-29,Tailoring magnetic insulator proximity effects in graphene: First-principles calculations,"We report a systematic first-principles investigation of the influence of
different magnetic insulators on the magnetic proximity effect induced in
graphene. Four different magnetic insulators are considered: two ferromagnetic
europium chalcogenides namely EuO and EuS and two ferrimagnetic insulators
yttrium iron garnet (YIG) and cobalt ferrite (CFO). The obtained
exchange-splitting varies from tens to hundreds of meV. We also find an
electron doping induced by YIG and europium chalcogenides substrates, that
shift the Fermi level up to 0.78 eV and 1.3 eV respectively, whereas hole
doping up to 0.5 eV is generated by CFO. Furthermore, we study the variation of
the extracted exchange and tight binding parameters as a function of the EuO
and EuS thicknesses. We show that those parameters are robust to thickness
variation such that a single monolayer of magnetic insulator can induce a large
magnetic proximity effect on graphene. Those findings pave the way towards
possible engineering of graphene spin-gating by proximity effect especially in
view of recent experiments advancement.",1610.09554v1
2017-02-07,Giant-spin nonlinear response theory of magnetic nanoparticle hyperthermia: a field dependence study,"Understanding high-field amplitude electromagnetic heat loss phenomena is of
great importance, in particular in the biomedical field, since the
heat-delivery treatment plans might rely on analytical models that are only
valid at low field amplitudes. Here, we develop a nonlinear response model
valid for single- domain nanoparticles of larger particle sizes and higher
field amplitudes in comparison to linear response theory. A nonlinear
magnetization expression and a generalized heat loss power equation are
obtained and compared with the exact solution of the stochastic
Landau-Lifshitz-Gilbert equation assuming the giant-spin hypothesis. The model
is valid within the hyperthermia therapeutic window and predicts a shift of
optimum particle size and distinct heat loss field amplitude exponents.
Experimental hyperthermia data with distinct ferrite-based nanoparticles, as
well as third harmonic magnetization data supports the nonlinear model, which
also has implications for magnetic particle imaging and magnetic thermometry.",1702.02022v1
2017-03-22,Fabrication and magnetic control of Y3Fe5O12 cantilevers,"We have fabricated ferrite cantilevers in which their vibrational properties
can be controlled by external magnetic fields. Submicron-scale cantilever
structures were made from Y3Fe5O12 (YIG) films by physical etching combined
with use of a focused ion beam milling technique. We found that the cantilevers
exhibit two resonance modes which correspond to horizontal and vertical
vibrations. Under external magnetic fields, the resonance frequency of the
horizontal mode increases, while that of the vertical mode decreases,
quantitatively consistent with our numerical simulation for magnetic forces.
The changes in resonance frequencies with magnetic fields reach a few percent,
showing that efficient magnetic control of resonance frequencies was achieved.",1703.07533v1
2017-03-22,Coexistence of Interfacial Stress and Charge Transfer in Graphene Oxide based Magnetic Nanocomposites,"In this paper, we establish the existence of both compressive stress and
charge transfer process in hydrothermally synthesized cobalt ferrite-graphene
oxide (CoFe2O4/GO) nanocomposites. Transmission electron microscopy (TEM)
results reveal the decoration of CoFe2O4 nanoparticles on GO sheets. Magnetic
response of nanocomposites was confirme from superconducting quantum
interference device (SQUID) magnetometer measurement. Optical properties of
these nanocomposites were investigated by Raman spectroscopy. Interfacial
compressive stress involved in this system is evaluated from observed blue
shift of characteristic G peak of graphene oxide. Increase in full width
half-maximum ( FWHM) as well as up shift in D and G peaks are clear indicator
of involvement of charge transfer process between GO sheets and dispersed
magnetic nanoparticles. The effect of charge transfer process is quantified in
terms of shifting of Fermi level of these nanocomposites. This is evaluated
from variation in contact surface potential difference (CPD) using Scanning
Kelvin probe microscopy (SKPM). XRD spectra of CoFe2O4/GO confirm the
polycrystalline nature of CoFe2O4 nanoparticles. Lattice strain estimated from
XRD peaks are correlated to the observed Raman shift.",1703.07545v1
2018-04-25,Nonreciprocity in microwave optomechanical circuits,"Nonreciprocal devices such as isolators and circulators are necessary to
protect sensitive apparatus from unwanted noise. Recently, a variety of
alternatives were proposed to replace ferrite-based commercial technologies,
with the motivation to be integrated with microwave superconducting quantum
circuits. Here, we review isolators realized with microwave optomechanical
circuits and present a gyrator-based picture to develop an intuition on the
origin of nonreciprocity in these systems. Such nonreciprocal optomechanical
schemes show promise as they can be extended to circulators and directional
amplifiers, with perspectives to reach the quantum limit in terms of added
noise.",1804.09599v1
2018-11-08,Quasistatic oscillations in subwavelength particles: Can one observe energy eigenstates?,"In increasing the capabilities of the optical and microwave techniques
further into the subwavelength regime, quasistatic resonant structures has
attracted considerable interest. Electromagnetic responses of electrostatic
(ES) plasmon resonances in optics and magnetostatic (MS) magnon resonances in
microwaves give rise to a strong enhancement of local fields near the surfaces
of subwavelength particles. In the near-field regions of subwavelength
particles one can only measure the electric or the magnetic field with
accuracy. Such uncertainty in definition of the electric or magnetic field
components raises the question of energy eigenstates of quasistatic
oscillations. The energy eigenstate problem can be properly formulated when
potential functions, used in the quasistatic-resonance problems, are introduced
as scalar wave functions. In this case, one should observe quasistatic-wave
retardation effects still staying in frames of the quasistatic description of
oscillations in a subwavelength particle. In this paper, we analyze the problem
of energy quantization of ES resonances in subwavelength optical metallic
structures with plasmon oscillations and MS resonances in subwavelength
microwave ferrite particles with magnon oscillations. We show that in a case of
MS-potential scalar wave function one can observe quasistatic retardation
effects and obtain a proper formulation of the energy eigenstate problem.",1811.03314v1
2018-11-14,Enhancing nanoparticle diffusion on a unidirectional domain wall magnetic ratchet,"The performance of nanoscale magnetic devices is often limited by the
presence of thermal fluctuations, while in micro-nanofluidic applications the
same fluctuations may be used to spread reactants or drugs. Here we demonstrate
the controlled motion and the enhancement of diffusion of magnetic
nanoparticles that are manipulated and driven across a series of Bloch walls
within an epitaxially grown ferrite garnet film. We use a rotating magnetic
field to generate a traveling wave potential that unidirectionally transports
the nanoparticles at a frequency tunable speed. Strikingly, we find an
enhancement of diffusion along the propulsion direction and a frequency
dependent diffusion coefficient that can be precisely controlled by varying the
system parameters. To explain the reported phenomena, we develop a theoretical
approach that shows a fair agreement with the experimental data enabling an
exact analytical expression for the enhanced diffusivity above the magnetically
modulated periodic landscape. Our technique to control thermal fluctuations of
driven magnetic nanoparticles represents a versatile and powerful way to
programmably transport magnetic colloidal matter in a fluid, opening the doors
to different fluidic applications based on exploiting magnetic domain wall
ratchets.",1811.05762v1
2019-05-08,Gradient-enhanced statistical analysis of cleavage fracture,"We present a probabilistic framework for brittle fracture that builds upon
Weibull statistics and strain gradient plasticity. The constitutive response is
given by the mechanism-based strain gradient plasticity theory, aiming to
accurately characterize crack tip stresses by accounting for the role of
plastic strain gradients in elevating local strengthening ahead of cracks. It
is shown that gradients of plastic strain elevate the Weibull stress and the
probability of failure for a given choice of the threshold stress and the
Weibull parameters. The statistical framework presented is used to estimate
failure probabilities across temperatures in ferritic steels. The framework has
the capability to estimate the three statistical parameters present in the
Weibull-type model without any prior assumptions. The calibration against
experimental data shows important differences in the values obtained for strain
gradient plasticity and conventional J2 plasticity. Moreover, local probability
maps show that potential damage initiation sites are much closer to the crack
tip in the case of gradient-enhanced plasticity. Finally, the fracture response
across the ductile-to-brittle regime is investigated by computing the cleavage
resistance curves with increasing temperature. Gradient plasticity predictions
appear to show a better agreement with the experiments.",1905.03221v1
2019-05-30,Radio Frequency Magnet-free Circulators Based on Spatiotemporal Modulation of Surface Acoustic Wave Filters,"In this paper, a new generation of magnet-free circulators with high
performance is proposed. Circulators are crucial devices in modern
communication systems due to their ability to enable full-duplexing and double
the spectral efficiency directly in the physical layer of the radio-frequency
(RF) front-end. Traditionally, Lorentz reciprocity is broken by applying
magnetic bias to ferrite materials, therefore conventional circulators are
bulky and expensive. In this paper, this problem is addressed by replacing the
magnetic bias with periodic spatiotemporal modulation. Compared to previous
works, the proposed circulator is constructed using surface acoustic wave (SAW)
filters instead of transmission lines (TL), which reduces the modulation
frequency by at least a factor of 20 and ensures ultra-low power consumption
and high linearity. The miniaturized high quality (Q) factor SAW filters also
lead to a low-loss non-reciprocal band with strong isolation (IX) and broad
bandwidth (BW) on a chip scale, therefore addressing such limitations in
previous magnet-free demonstrations. Furthermore, compared to the conventional
differential circuit configuration, a novel quad configuration is developed,
which doubles the intermodulation-free bandwidth.",1905.13252v1
2010-05-13,Short-Range B-site Ordering in Inverse Spinel Ferrite NiFe2O4,"The Raman spectra of single crystals of NiFe2O4 were studied in various
scattering configurations in close comparison with the corresponding spectra of
Ni0.7Zn0.3Fe2O4 and Fe3O4. The number of experimentally observed Raman modes
exceeds significantly that expected for a normal spinel structure and the
polarization properties of most of the Raman lines provide evidence for a
microscopic symmetry lower than that given by the Fd-3m space group. We argue
that the experimental results can be explained by considering the short range
1:1 ordering of Ni2+ and Fe3+ at the B-sites of inverse spinel structure, most
probably of tetragonal P4_122/P4_322 symmetry.",1005.2244v1
2013-08-13,Interface states in CoFe2O4 spin-filter tunnel junctions,"Spin-filter tunneling is a promising way to generate highly spin-polarized
current, a key component for spintronics applications. In this work we explore
the tunneling conductance across the spin-filter material CoFe2O4 interfaced
with Au electrodes, a geometry which provides nearly perfect lattice matching
at the CoFe2O4/Au(001) interface. Using density functional theory calculations
we demonstrate that interface states play a decisive role in controlling the
transport spin polarization in this tunnel junction. For a realistic CoFe2O4
barrier thickness, we predict a tunneling spin polarization of about -60%. We
show that this value is lower than what is expected based solely on
considerations of the spin-polarized band structure of CoFe2O4, and therefore
that these interface states can play a detrimental role. We argue this is a
rather general feature of ferrimagnetic ferrites and could make an important
impact on spin-filter tunneling applications.",1308.3461v1
2014-03-20,Magnetization of densely packed interacting magnetic nanoparticles with cubic and uniaxial anisotropies: A Monte Carlo study,"The magnetization curves of densely packed single domain magnetic
nanoparticles (MNP) are investigated by Monte Carlo simulations in the
framework of an effective one spin model. The particles whose size
polydispersity is taken into account are arranged in spherical clusters and
both dipole dipole interactions (DDI) and magnetic anisotropy energy (MAE) are
included in the total energy. Having in mind the special case of spinel
ferrites of intrinsic cubic symmetry, combined cubic and uniaxial
magnetocrystalline anisotropies are considered with different configurations
for the orientations of the cubic and uniaxial axes. It is found that the DDI,
together with a marked reduction of the linear susceptibility are responsible
for a damping of the peculiarities due to the MAE cubic component on the
magnetization. As an application, we show that the simulated magnetization
curves compare well to experimental results for $\gamma$--Fe$_2$O$_3$ MNP for
small to moderate values of the field.",1403.5157v1
2017-01-05,Transforming Single Domain Magnetic CoFe2O4 Nanoparticles from Hydrophobic to Hydrophilic By Novel Mechanochemical Ligand Exchange,"Single phase, uniform size (~9 nm) Cobalt Ferrite (CFO) nanoparticles have
been synthesized by hydrothermal synthesis using oleic acid as a surfactant.
The as synthesized oleic acid coated CFO (OA-CFO) nanoparticles were well
dispersible in nonpolar solvents but not dispersible in water. The OA-CFO
nanoparticles have been successfully transformed to highly water dispersible
citric acid coated CFO (CA-CFO) nanoparticles using a novel single step ligand
exchange process by mechanochemical milling, in which small chain citric acid
molecules replace the original large chain oleic acid molecules available on
CFO nanoparticles. The contact angle measurement shows that OA-CFO
nanoparticles are hydrophobic whereas CA-CFO nanoparticles are superhydrophilic
in nature. The potentiality of as synthesized OA-CFO and mechanochemically
transformed CA-CFO nanoparticles for the demulsification of highly stabilized
water-in-oil and oil-in-water emulsions has been demonstrated.",1701.01410v1
2017-01-08,Nonlocal magnon spin transport in NiFe$_2$O$_4$ thin films,"We report magnon spin transport in nickel ferrite (NiFe$_2$O$_4$, NFO)/
platinum (Pt) bilayer systems at room temperature. A nonlocal geometry is
employed, where the magnons are excited by the spin Hall effect or by the Joule
heating induced spin Seebeck effect at the Pt injector, and detected at a
certain distance away by the inverse spin Hall effect at the Pt detector. The
dependence of the nonlocal magnon spin signals as a function of the magnetic
field is closely related to the NFO magnetization behavior. In contrast, we
observe that the magnetoresistance measured locally at the Pt injector does not
show a clear relation with the average NFO magnetization. We estimate the
magnon spin relaxation length to be 3.1 $\pm$ 0.2 $\mu$m in the investigated
NFO samples.",1701.02041v2
2011-11-08,Analysis of the Collective Behavior of a 10 by 10 Array of Fe3O4 Dots in a Large Micromagnetic Simulation,"We report a full (3D) micromagnetic simulation of a set of 100 ferrite
(Fe$_3$O$_4$) cylindrical dots, arranged in a 10 by 10 square (planar) array of
side 3.27 $\mu$m, excited by an external in-plane magnetic field. The resulting
power spectrum of magnetic excitations and the dynamical magnetization field at
the resulting resonance modes were investigated. The absorption spectrum
deviates considerably from that of a single particle reference simulation,
presenting a mode-shifting and splitting effect. We found an inversion symmetry
through the center of the array, in the sense that each particle and its
inversion counterpart share approximately the same magnetization mode behavior.
Magnonic designs aiming at synchronous or coherent tunings of spin-wave
excitations at given spatially separated points within a regular square array
may benefit from the new effects here described.",1111.1866v1
2012-04-03,Two-pulse stimulated echo in magnets,"The results of experimental study of two-pulse stimulated echo in
ferromagnets of two types are presented. Ferromagnet Co and half-metal Co MnSi
2, in which a single-pulse echo formed by the distortion mechanism of the
fronts of exciting pulse is also observed, are classified among the first type.
Lithium ferrite and intermetal compound MnSb characterized by the absence of
single-pulse echo in them - belong to the second type. For signals of two-pulse
stimulated echo in the materials of the first type a short time and a long time
of relaxations are observed. The short time is about the order of value shorter
less than the spin-spin relaxation time. The long time is close to the
transverse relaxation time of single-pulse echo formed by the distortion
mechanism. The mechanisms that provide the possible interpretations of the
peculiarities of the processes of nuclear magnetic relaxation are discussed.",1204.0686v2
2012-04-26,Peculiarities of timing and spectral diagrams of magnetic video-pulse excitation influence on NMR spin-echo in magnets,"We present the first systematic study of timing and spectral diagrams of
magnetic video-pulse influence on the NMR two-pulse echo in a number of magnets
(ferromagnets, ferrites, half metals, intermetals). It is shown that the timing
diagrams showing the dependence of two-pulse echo intensity on the temporal
location of a magnetic video-pulse in respect to radio-frequency pulses and the
spectral diagrams of this influence are defined mainly by the local hyperfine
field anisotropy and domain walls mobility. These diagrams could be used for
the identification of the nature of NMR spectra in multidomain magnetic
materials and to improve the resolution capacity of the NMR method in magnets.",1204.5844v1
2013-09-20,High values of Ferroelectric polarization and magnetic susceptibility in BFO nanorods,"Remarkably high values of polarization as well as a significant magnetic
susceptibility have been observed in multiferroic Bismuth Ferrite (BFO) in the
form of nanorods protruding out. These were developed on porous Anodised
Alumina (AAO) templates using wet chemical technique. Diameters of nanorods are
in the range of 20-100 nm. The high values of polarization and magnetic
susceptibility are attributed to the BFO nanorod structures giving rise to the
directionality. There is no leakage current in P-E loop examined at various
frequencies. Magnetocapacitance measurements reflect a significant enhancement
in magnetoelectric coupling also.",1309.5218v2
2013-09-23,Remarkably high value of Capacitance in BiFeO3 Nanorod,"A remarkably high value of specific capacitance of 450 F/g has been observed
through electrochemical measurements in the electrode made of multiferroic
Bismuth Ferrite (BFO) in the form of nanorods protruding out. These BFO
nanorods were developed on porous Anodised Alumina (AAO) templates using wet
chemical technique. Diameters of nanorods were in the range of 20-100 nm. The
high capacitance is attributed to the nanostructure. The active surface charge
has been evaluated electrochemically by cyclic voltammetry (CV) at different
scanning rates and charge-discharge studies. The specific capacitances were
constant after several cycles of charge-discharge leading to their useful
application in devices. The mechanism of accumulation of charge on the
electrode surface has been studied.",1309.5690v1
2014-06-05,Magnetic properties of epitaxial Fe$_3$O$_4$ films with various crystal orientations and TMR effect in room temperature,"Fe$_3$O$_4$ is a ferrimagnetic spinel ferrite that exhibits electric
conductivity at room temperature (RT). Although the material has been predicted
to be a half metal according to ab-initio calculations, magnetic tunnel
junctions (MTJs) with Fe$_3$O$_4$ electrodes have demonstrated a small tunnel
magnetoresistance effect. Not even the sign of the TMR ratio has been
experimentally established. Here, we report on the magnetic properties of
epitaxial Fe$_3$O$_4$ films with various crystal orientations. The films
exhibited apparent crystal orientation dependence on hysteresis curves. In
particular, Fe$_3$O$_4$(110) films exhibited in-plane uniaxial magnetic
anisotropy. With respect to the squareness of hysteresis, Fe$_3$O$_4$ (111)
demonstrated the largest squareness. Furthermore, we fabricated MTJs with
Fe$_3$O$_4$(110) electrodes, and obtained an TMR effect of -12\% at RT. The
negative TMR ratio corresponded to the negative spin polarization of
Fe$_3$O$_4$ predicted from band calculations.",1406.1296v1
2014-06-14,Electric-field coupling to spin waves in a centrosymmetric ferrite,"We experimentally demonstrate that the spin-orbit interaction can be utilized
for direct electric-field tuning of the propagation of spin waves in a
single-crystal yttrium iron garnet magnonic waveguide. Magnetoelectric coupling
not due to the spin-orbit interaction, and hence an order of magnitude weaker,
leads to electric-field modification of the spin-wave velocity for waveguide
geometries where the spin-orbit interaction will not contribute. A theory of
the phase shift, validated by the experiment data, shows that, in the exchange
spin wave regime, this electric tuning can have high efficiency. Our findings
point to an important avenue for manipulating spin waves and developing
electrically tunable magnonic devices.",1406.3675v1
2014-06-16,An air-cooled Litz wire coil for measuring the high frequency hysteresis loops of magnetic samples : a useful setup for magnetic hyperthermia applications,"A low-cost and simple setup for measuring the high-frequency hysteresis loops
of magnetic samples is described. An AMF in the range 6-100 kHz with amplitude
up to 80 mT is produced by a Litz wire coil. The latter is air-cooled using a
forced-air approach so no water flow is required to run the setup.
High-frequency hysteresis loops are measured using a system of pick-up coils
and numerical integration of signals. Reproducible measurements are obtained in
the frequency range of 6-56 kHz. Measurement examples on ferrite cylinders and
on iron oxide nanoparticle ferrofluids are shown. Comparison with other
measurement methods of the hysteresis loop area (complex susceptibility,
quasi-static hysteresis loops and calorific measurements) is provided and shows
the coherency of the results obtained with this setup. This setup is well
adapted to the magnetic characterization of colloidal solutions of MNPs for
magnetic hyperthermia applications.",1406.4013v1
2014-06-20,Linear magnetoelectricity at room temperature in perovskite superlattices by design,"Discovering materials that display a linear magnetoelectric effect at room
temperature is challenge. Such materials could facilitate novel devices based
on the electric-field control of magnetism. Here we present simple, chemically
intuitive design rules to identify a new class of bulk magnetoelectric
materials based on the 'bicolor' layering of $Pnma$ ferrite perovskites, e.g.,
LaFeO$_3$/ LnFeO$_3$ superlattices for which Ln = lanthanide cation. We use
first-principles density-functional theory calculations to confirm these ideas.
Additionally, we elucidate the origin of this effect and show it is a general
consequence of the layering of any bicolor, $Pnma$ perovskite superlattice in
which the number of constituent layers are odd (leading to a form of hybrid
improper ferroelectricity) and Goodenough- Kanamori rules. Here, the polar
distortions induce both weak ferromagnetism and a linear magnetoelectric
effect. Our calculations suggest that the effect is 2-3 times greater in
magnitude than that observed for the prototypical magnetoelectric material,
Cr$_2$O$_3$. We use a simple mean field model to show that the considered
materials order magnetically above room temperature.",1406.5488v1
2015-12-04,Magnetoelectric-field microwave antennas: Far-field orbital angular momenta from chiral-topology near fields,"The near fields in the proximity of a small ferrite particle with
magnetic-dipolar-mode (MDM) oscillations have space and time symmetry
breakings. Such MDM originated fields, called magnetoelectric (ME) fields,
carry both spin and orbital angular momentums. By virtue of unique topology, ME
fields are strongly different from free-space electromagnetic (EM) fields. In
this paper, we show that because of chiral topology of ME fields in a nearfield
region, far-field orbital angular momenta (OAM) can be observed, both
numerically and experimentally. In a single element antenna, we obtain a
radiation pattern with an angular squint. We reveal that in far field microwave
radiation a crucial role is played by the ME energy distribution in the
near-field region.",1512.01393v1
2015-12-18,Cross-spectrum Measurement of Thermal-noise Limited Oscillators,"Cross-spectrum analysis is a commonly-used technique for the detection of
phase and amplitude noise of a signal in the presence of interfering noise. It
extracts the desired correlated noise from two time series in the presence of
uncorrelated interfering noise. Recently, we demonstrated that the
phase-inversion (anti-correlation) effect due to AM noise leakage can cause
complete or partial collapse of the cross-spectral function. In this paper, we
discuss the newly discovered effect of anti-correlated thermal noise that
originates from the common-mode power divider (splitter), an essential
component in a cross-spectrum noise measurement system. We studied this effect
for different power splitters and discuss its influence on the measurement of
thermal-noise limited oscillators. An oscillator whose thermal noise is
primarily set by the 50 ohm source resistance is referred to as a
thermally-limited oscillator. We provide theory, simulation and experimental
results. In addition, we expand this study to reveal how the presence of
ferrite-isolators and amplifiers at the output ports of the power splitters can
affect the oscillator noise measurements. Finally, we discuss a possible
solution to overcome this problem.",1512.06160v1
2016-05-10,Engineering topological materials in microwave cavity arrays,"We present a scalable architecture for the exploration of interacting
topological phases of photons in arrays of microwave cavities, using
established techniques from cavity and circuit quantum electrodynamics. A
time-reversal symmetry breaking (non-reciprocal) flux is induced by coupling
the microwave cavities to ferrites, allowing for the production of a variety of
topological band structures including the $\alpha=1/4$ Hofstadter model.
Effective photon-photon interactions are included by coupling the cavities to
superconducting qubits, and are sufficient to produce a $\nu=1/2$ bosonic
Laughlin puddle. We demonstrate by exact diagonalization that this architecture
is robust to experimentally achievable levels of disorder. These advances
provide an exciting opportunity to employ the quantum circuit toolkit for the
exploration of strongly interacting topological materials.",1605.03177v1
2016-05-24,Autocatalytic mechanism of pearlite transformation in steel,"A model of pearlite colony formation in carbon steels with ab-initio
parameterization is proposed. The model describes the process of decomposition
of austenite and cementite formation through a metastable intermediate
structure by taking into account the increase of the magnetic order under the
cooling. Autocatalytic mechanism of pearlite colony formation and the
conditions for its implementation have been analyzed. We demonstrate that
pearlite with lamellar structure is formed by autocatalytic mechanism when
thermodynamic equilibrium between the initial phase (austenite) and the
products of its decomposition (cementite and ferrite) does not take place. By
using model expression for free energy with first-principles parameterization
we find conditions of formation of both lamellar and globular structures, in
agreement with experiment. The transformation diagram is suggested and
different scenarios in the kinetics of decomposition are investigated by phase
field simulations.",1605.07508v2
2016-08-26,Optimization of nanocomposite materials for permanent magnets by micromagnetic simulations: effect of the intergrain exchange and the hard grains shape,"In this paper we perform the detailed numerical analysis of remagnetization
processes in nanocomposite magnetic materials consisting of magnetically hard
grains (i.e. grains made of a material with a high magnetocrystalline
anisotropy) embedded into a magnetically soft phase. Such materials are widely
used for the production of permanent magnets, because they combine the high
remanence with the large coercivity. We perform simulations of nanocomposites
with Sr-ferrite as the hard phase and Fe or Ni as the soft phase, concentrating
our efforts on analyzing the effects of ({\it i}) the imperfect intergrain
exchange and ({\it ii}) the non-spherical shape of hard grains. We demonstrate
that - in contrast to the common belief - the maximal energy product is
achieved not for systems with the perfect intergrain exchange, but for
materials where this exchange is substantially weakened. We also show that the
main parameters of the hysteresis loop - remanence, coercivity and the energy
product - exhibit non-trivial dependencies on the shape of hard grains, and
provide detailed explanations for our results. Simulation predictions obtained
in this work open new ways for the optimization of materials for permanent
magnets.",1608.07429v1
2017-06-15,Preliminary corrosion studies of IN-RAFM steel with stagnant Lead Lithium at 550 C,"Corrosion of Indian RAFMS (reduced activation ferritic martensitic steel)
material with liquid metal, Lead Lithium ( Pb-Li) has been studied under static
condition, maintaining Pb-Li at 550 C for different time durations, 2500, 5000
and 9000 hours. Corrosion rate was calculated from weight loss measurements.
Microstructure analysis was carried out using SEM and chemical composition by
SEM-EDX measurements. Micro Vickers hardness and tensile testing were also
carried out. Chromium was found leaching from the near surface regions and
surface hardness was found to decrease in all the three cases. Grain boundaries
were affected. Some grains got detached from the surface giving rise to pebble
like structures in the surface micrographs. There was no significant reduction
in the tensile strength, after exposure to liquid metal. This paper discusses
the experimental details and the results obtained.",1706.05000v1
2017-06-26,Magnetic Proximity Effect in Pt/CoFe2O4 Bilayers,"We observe the magnetic proximity effect (MPE) in Pt/CoFe2O4 bilayers grown
by molecular beam epitaxy. This is revealed through angle-dependent
magnetoresistance measurements at 5 K, which isolate the contributions of
induced ferromagnetism (i.e. anisotropic magnetoresistance) and spin Hall
effect (i.e. spin Hall magnetoresistance) in the Pt layer. The observation of
induced ferromagnetism in Pt via AMR is further supported by density functional
theory calculations and various control measurements including insertion of a
Cu spacer layer to suppress the induced ferromagnetism. In addition, anomalous
Hall effect measurements show an out-of-plane magnetic hysteresis loop of the
induced ferromagnetic phase with larger coercivity and larger remanence than
the bulk CoFe2O4. By demonstrating MPE in Pt/CoFe2O4, these results establish
the spinel ferrite family as a promising material for MPE and spin manipulation
via proximity exchange fields.",1706.08473v1
2017-06-22,Investigation on nickel ferrite nanowire device exhibiting negative differential resistance $-$ a first-principles investigation,"The electronic property of NiFe$_2$O$_4$ nanowire device is investigated
through nonequilibrium Green's functions (NEGF) in combination with density
functional theory (DFT). The electronic transport properties of NiFe$_2$O$_4$
nanowire are studied in terms of density of states, transmission spectrum and
$I{-}V$ characteristics. The density of states gets modified with the applied
bias voltage across NiFe$_2$O$_4$ nanowire device, the density of charge is
observed both in the valence band and in the conduction band on increasing the
bias voltage. The transmission spectrum of NiFe$_2$O$_4$ nanowire device gives
the insights on the transition of electrons at different energy intervals. The
findings of the present work suggest that NiFe$_2$O$_4$ nanowire device can be
used as negative differential resistance (NDR) device and its NDR property can
be tuned with the bias voltage, which may be used in microwave device, memory
devices and in fast switching devices.",1706.10148v1
2017-10-24,Peculiar metastable structural state in carbon steel,"The kinetics of phase transformations at cooling of carbon steel in
dependence on the temperature of preliminary annealing T$_{an}$ is studied. It
is shown that the cooling from T$_{an}$ > A$_3$ (i. e. above the temperature of
ferrite start) with the rate 90 - 100 K/s results in structural state which
essentially dependent on T$_{an}$; at 750$^0$C < T$_{an}$ < 830$^0$C the
transformation is of perlite type whereas at T$_{an}$ > 830$^0$C the
martensitic structure arises. Our results evidence the formation of a special
structural state in a certain range of temperatures near and above the boundary
of two phase region which is characterized by a substantially nanoscale
heterogeneity in carbon distribution, lattice distortions, and magnetic
short-range order.",1710.08604v1
2017-12-16,Contrasting magnetoelectric behavior in multiferroic hexaferrites as understood by crystal symmetry analyses,"Magnetoelectric (ME) properties under rotating magnetic field H are
comparatively investigated in two representative hexaferrites Y-type
Ba0.5Sr1.5Zn2(Fe0.92Al0.08)12O22 and Z-type Ba0.52Sr2.48Co2Fe24O41, both of
which have exhibited a similar transverse conical spin structure and giant ME
coupling near room temperature. When the external H is rotated clockwise by
2pi, in-plane P vector is rotated clockwise by 2pi in the Y-type hexaferrite
and counterclockwise by 4pi in the Z-type hexaferrite. A symmetry-based
analysis reveals that the faster and opposite rotation of P vector in the
Z-type hexaferrite is associated with the existence of a mirror plane
perpendicular to c-axis. Moreover, such a peculiar crystal symmetry also
results in contrasting microscopic origins for the spin-driven
ferroelectricity; only the inverse DM interaction is responsible for the Y-type
hexaferrite while additional p-d hybridization becomes more important in the
Z-type hexaferrite. This work demonstrates the importance of the crystal
symmetry in the determination of ME properties in the hexaferrites and provides
a fundamental framework for understanding and applying the giant ME coupling in
various ferrites with hexagonal crystal structure.",1712.05928v1
2018-10-07,Gazing at crystal balls: Electron backscatter diffraction pattern analysis and cross correlation on the sphere,"We present spherical analysis of electron backscatter diffraction (EBSD)
patterns with two new algorithms: (1) band localisation and band profile
analysis using the spherical Radon transform; (2) orientation determination
using spherical cross correlation. These new approaches are formally introduced
and their accuracies are determined using dynamically simulated patterns. We
demonstrate their utility with an experimental dataset obtained from ferritic
iron. Our results indicate that the analysis of EBSD patterns on the surface of
the sphere provides an elegant method of revealing information from these rich
sources of crystallographic data.",1810.03211v4
2019-06-03,Oxygen-vacancy induced magnetic phase transitions in multiferroic thin films,"Multiferroics in which giant ferroelectric polarization and magnetism coexist
are of tremendous potential for engineering disruptive applications in
information storage and energy conversion. Yet the functional properties of
multiferroics are thought to be affected detrimentally by the presence of point
defects, which may be abundant due to the volatile nature of some constituent
atoms and high temperatures involved in materials preparation. Here, we
demonstrate with theoretical methods that oxygen vacancies may enhance the
functionality of multiferroics by radically changing their magnetic
interactions in thin films. Specifically, oxygen vacancies may restore missing
magnetic super-exchange interactions in large axial ratio phases, leading to
full antiferromagnetic spin ordering, and induce the stabilization of
ferrimagnetic states with a significant net magnetization of 0.5 uB per formula
unit. Our theoretical study should help to clarify the origins of long-standing
controversies in bismuth ferrite and improve the design of technological
applications based on multiferroics.",1906.01117v1
2019-06-11,Proximity magnetoresistance in graphene induced by magnetic insulators,"We demonstrate the existence of Giant proximity magnetoresistance (PMR)
effect in a graphene spin valve where spin polarization is induced by a nearby
magnetic insulator. PMR calculations were performed for yttrium iron garnet
(YIG), cobalt ferrite (CFO), and two europium chalcogenides EuO and EuS. We
find a significant PMR (up to 100%) values defined as a relative change of
graphene conductance with respect to parallel and antiparallel alignment of two
proximity induced magnetic regions within graphene. Namely, for high Curie
temperature (Tc) CFO and YIG insulators which are particularly important for
applications, we obtain 22% and 77% at room temperature, respectively. For low
Tc chalcogenides, EuO and EuS, the PMR is 100% in both cases. Furthermore, the
PMR is robust with respect to system dimensions and edge type termination. Our
findings show that it is possible to induce spin polarized currents in graphene
with no direct injection through magnetic materials.",1906.04469v1
2019-09-06,Unveiling multiferroic proximity effect in graphene,"We demonstrate that electronic and magnetic properties of graphene can be
tuned via proximity of multiferroic substrate. Our first-principles
calculations performed both with and without spin-orbit coupling clearly show
that by contacting graphene with bismuth ferrite BiFeO$_3$ (BFO) film, the
spin-dependent electronic structure of graphene is strongly impacted both by
the magnetic order and by electric polarization in the underlying BFO. Based on
extracted Hamiltonian parameters obtained from the graphene band structure, we
propose a concept of six-resistance device based on exploring multiferroic
proximity effect giving rise to significant proximity electro- (PER), magneto-
(PMR), and multiferroic (PMER) resistance effects. This finding paves a way
towards multiferroic control of magnetic properties in two dimensional
materials.",1909.02844v1
2019-09-07,Designing rare-earth free permanent magnets in Heusler alloys via interstitial doping,"Based on high-throughput density functional theory calculations, we
investigated the effects of light interstitial H, B, C, and N atoms on the
magnetic properties of cubic Heusler alloys, with the aim to design new
rare-earth free permanent magnets. It is observed that the interstitial atoms
induce significant tetragonal distortions, leading to 32 candidates with large
($>$ 0.4 MJ/m$^3$) uniaxial magneto-crystalline anisotropy energies (MAEs) and
10 cases with large in-plane MAEs. Detailed analysis following the the
perturbation theory and chemical bonding reveals the strong MAE originates from
the local crystalline distortions and thus the changes of the chemical bonding
around the interstitials. This provides a valuable way to tailor the MAEs to
obtain competitive permanent magnets, filling the gap between high performance
Sm-Co/Nd-Fe-B and widely used ferrite/AlNiCo materials.",1909.03275v1
2019-10-15,Achievements and New Challenges for CERN's Digital LLRF Family,"An innovative digital Low-Level RF (LLRF) family has been developed at CERN
and deployed on several circular machines. Operation of CERN's PS Booster
(PSB), Low Energy Ion Ring (LEIR) and Extra Low ENergy Antiproton (ELENA) ring
all reaped great benefit from the flexibility and processing power of this new
family. Beam and cavity feedback loops have been implemented, as well as bunch
shaping, longitudinal blowup and bunch splitting. For ELENA, longitudinal
diagnostics such as bunched beam intensity and bunch length measurements have
also been deployed. During Long Shutdown 2 (LS2) the ferrite-based High-Level
RF (HLRF) systems of the Antiproton Decelerator (AD) and of the four-ring PSB
will be replaced with Finemet-based HLRF. This will require a new LLRF system
for the AD and deep upgrades to the existing PSB LLRF systems. This paper gives
an overview of the main results achieved by the digital LLRF family so far and
of the challenges the LLRF team will take on during LS2.",1910.06643v1
2020-01-09,"High temperature thermal cycling effect on the irreversible responses of lattice structure, magnetic properties and electrical conductivity in Co$_{2.75}$Fe$_{0.25}$O$_{4+δ}$ spinel oxide","We report high temperature synchrotron X-ray diffraction (SXRD), dc
magnetization and current-voltage (I-V) characteristics for the samples of
Co$_{2.75}$Fe$_{0.25}$O$_4$ ferrite. The material was prepared by chemical
reaction of the Fe and Co nitrate solutions at pH = 11 and subsequent annealing
at temperatures 200 0C, 500 0C and 900 0C. The measurements were performed by
cycling the temperature from 300 K to high temperature (warming mode) and
return back to 300 K (cooling mode). The SXRD patterns indicated a fine
bi-phased cubic spinel structure in the highly Co rich spinel oxide.
Magnetization curves showed intrinsic ferrimagnetic features and defect induced
additional ferromagnetic phase at higher temperatures. Electrical conductivity
showed thermal hysteresis loop between warming and cooling modes of temperature
variation. The samples exhibited new information on the irreversibility
phenomena of lattice structure, magnetization and electrical conductivity on
cycling the measurement temperatures.",2001.02829v2
2020-01-27,Non-exponential magnetic relaxation in magnetic nanoparticles for hyperthermia,"Magnetic nanoparticle based hyperthermia emerged as a potential tool for
treating malignant tumours. The efficiency of the method relies on the
knowledge of magnetic properties of the samples; in particular, knowledge of
the frequency dependent complex magnetic susceptibility is vital to optimize
the irradiation conditions and to provide feedback for material science
developments. We study the frequency-dependent magnetic susceptibility of an
aqueous ferrite suspension for the first time using non-resonant and resonant
radiofrequency reflectometry. We identify the optimal measurement conditions
using a standard solenoid coil, which is capable of providing the complex
magnetic susceptibility up to 150 MHz. The result matches those obtained from a
radiofrequency resonator for a few discrete frequencies. The agreement between
the two different methods validates our approach. Surprisingly, the dynamic
magnetic susceptibility cannot be explained by an exponential magnetic
relaxation behavior even when we consider a particle size-dependent
distribution of the relaxation parameter.",2001.09774v1
2020-02-11,Diffusion of single active-dipolar cubes in applied fields,"""Active matter"" refers to a class of out-of-equilibrium systems whose ability
to transform environmental energy to kinetic energy is sought after in multiple
fields of science and at very different length scales. At microscopic scales,
an important challenge lies in overpowering the particles reorientation due to
thermal fluctuations, especially in nano-sized systems, to create non-random,
directed motion, needed for a wide range of possible applications. In this
article, we employ molecular dynamics simulations to show that the diffusion of
a self-propelling dipolar nanocube can be enhanced in a pre-defined direction
with the help of a moderately strong applied magnetic field, overruling the
effect of the thermal fluctuations. Furthermore, we show that the direction of
diffusion is given by the orientation of the net internal magnetisation of the
cube. This can be used to determine experimentally the latter in synthetically
crafted active cobalt ferrite nanocubes.",2002.04299v2
2021-01-19,Role of interface morphology on the martensitic transformation in pure Fe,"Using classical molecular dynamics simulations, we study austenite to ferrite
phase transformation in iron, focusing on the role of interface morphology. We
compare two different morphologies; a \textit{flat} interface in which the two
phases are joined according to Nishiyama-Wasserman orientation relationship vs.
a \textit{ledged} one, having steps similar to the vicinal surface. We identify
the atomic displacements along a misfit dislocation network at the interface
leading to the phase transformation. In case of \textit{ledged} interface,
stacking faults are nucleated at the steps, which hinder the interface motion,
leading to a lower mobility of the inter-phase boundary, than that of flat
interface. Interestingly, we also find the temperature dependence of the
interface mobility to show opposite trends in case of \textit{flat} vs.
\textit{ledged} boundary. We believe that our study is going to present a
unified and comprehensive view of martensitic transformation in iron with
different interface morphology, which is lacking at present, as \textit{flat}
and \textit{ledged} interfaces are treated separately in the existing
literature.",2101.07468v1
2012-05-21,Resistive and ferritic-wall plasma dynamos in a sphere,"We numerically study the effects of varying electric conductivity and
magnetic permeability of the bounding wall on a kinematic dynamo in a sphere
for parameters relevant to Madison plasma dynamo experiment (MPDX). The dynamo
is excited by a laminar, axisymmetric flow of von Karman type. The flow is
obtained as a solution to the Navier-Stokes equation for an isothermal fluid
with a velocity profile specified at the sphere's boundary. The properties of
the wall are taken into account as thin-wall boundary conditions imposed on the
magnetic field. It is found that an increase in the permeability of the wall
reduces the critical magnetic Reynolds number Rm_cr. An increase in the
conductivity of the wall leaves Rm_cr unaffected, but reduces the dynamo growth
rate.",1205.4696v1
2017-05-12,High voltage charging system for pulsed power generators,"A robust and portable power supply has been developed specifically for
charging linear transformer drivers, a modern incarnation of fast pulsed power
generators. It is capable of generator +100 kV and -100 kV at 1 mA, while
withstanding the large voltage spikes generated when the pulsed-power generator
is triggered. The three-stage design combines a zero-voltage switching circuit,
a step-up transformer using ferrite cores, and a dual Cockcroft-Walton voltage
multiplier. The zero-voltage switching circuit drives the primary of the
transformer in parallel with a capacitor. With this driver, the tank circuit
naturally remain in its resonant state, allowing for maximum energy coupling
between the zero-voltage switching circuit and the Cockcroft-Walton voltage
multiplier across a wide range of loading conditions.",1705.06240v2
2017-05-24,Control of single-mode operation in a circular waveguide filled by a longitudinally magnetized gyroelectromagnetic medium,"A substantial control of dispersion features of the hybrid EH01 and HE11
modes of a circular waveguide which is completely filled by a longitudinally
magnetized composite finely-stratified ferrite-semiconductor structure is
discussed. A relation between the resonant conditions of such a composite
gyroelectromagnetic filling of the circular waveguide and dispersion features
of the supported modes are studied. Three distinct frequency bands with the
single-mode operation under normal as well as anomalous dispersion conditions
of the EH01 mode are identified by solving an optimization problem with respect
to the filling factors of the composite medium. The possibility of achieving
isolated propagation of the HE11 mode is revealed.",1705.08603v1
2018-03-26,Uniaxial anisotropy and enhanced magnetostriction of CoFe$_2$O$_4$ induced by reaction under uniaxial pressure with SPS,"In this study, we have compared magnetic and magnetostrictive properties of
polycrystalline CoFe$_2$O$_4$ pellets, produced by three different methods,
focusing on the use of Spark Plasma Sintering (SPS). This technique allows a
very short heat treatment stage while a uniaxial pressure is applied. SPS was
utilized to sinter cobalt ferrite but also to make the reaction and the
sintering (reactive sintering) of the same ceramic composition. Magnetic and
magnetostrictive measurements show that the reactive sintering with SPS induces
a uniaxial anisotropy, while it is not the case with a simple sintering
process. The induced anisotropy is then expected to be a consequence of the
reaction under uniaxial pressure. This anisotropy enhanced the magnetostrictive
properties of the sample, where a maximum longitudinal magnetostriction of
$-229$~ppm is obtained. This process can be a promising alternative to the
magnetic-annealing because of the short processing time required (22 minutes).",1803.09656v1
2018-07-24,Enhanced magnon spin transport in NiFe$_2$O$_4$ thin films on a lattice-matched substrate,"We investigate magnon spin transport in epitaxial nickel ferrite
(NiFe$_2$O$_4$, NFO) films grown on magnesium gallate spinel (MgGa$_2$O$_4$,
MGO) substrates, which have a lattice mismatch with NFO as small as 0.78%,
resulting in the reduction of antiphase boundary defects and thus in improved
magnetic properties in the NFO films. In the nonlocal transport experiments,
enhanced signals are observed for both electrically and thermally excited
magnons, and the magnon relaxation length ($\lambda_m$) of NFO is found to be
around 2.5 $\mu$m at room temperature. Moreover, at both room and low
temperatures, we present distinct features from the nonlocal spin Seebeck
signals which arise from magnon polaron formation. Our results demonstrate
excellent magnon transport properties (magnon spin conductivity, $\lambda_m$
and spin mixing conductance at the interface between Pt) of NFO films grown on
a lattice-matched substrate that are comparable with those of yttrium iron
garnet.",1807.09013v1
2018-08-22,Microwave Conductivity of Ferroelectric Domains and Domain Walls in Hexagonal Rare-earth Ferrite,"We report the nanoscale electrical imaging results in hexagonal
$Lu_{0.6}Sc_{0.4}FeO_3$ single crystals using conductive atomic force
microscopy (C-AFM) and scanning microwave impedance microscopy (MIM). While the
dc and ac response of the ferroelectric domains can be explained by the surface
band bending, the drastic enhancement of domain wall (DW) ac conductivity is
clearly dominated by the dielectric loss due to DW vibration rather than
mobile-carrier conduction. Our work provides a unified physical picture to
describe the local conductivity of ferroelectric domains and domain walls,
which will be important for future incorporation of electrical conduction,
structural dynamics, and multiferroicity into high-frequency nano-devices.",1808.07208v1
2018-12-20,Size-dependent bistability in multiferroic nanoparticles,"Most multiferroic materials with coexisting ferroelectric and magnetic order
exhibit cycloidal antiferromagnetism with wavelength of several nanometers. The
prototypical example is bismuth ferrite (BiFeO$_3$ or BFO), a room-temperature
multiferroic considered for a number of technological applications. While most
applications require small sizes such as nanoparticles, little is known about
the state of these materials when their sizes are comparable to the cycloid
wavelength. This work describes a microscopic theory of cycloidal magnetism in
nanoparticles based on Hamiltonian calculations. It is demonstrated that
magnetic anisotropy close to the surface has a huge impact on the multiferroic
ground state. For certain nanoparticle sizes the modulus of the ferromagnetic
and ferroelectric moments are bistable, an effect that may be used in the
design of ideal memory bits that can be switched electrically and read out
magnetically.",1812.08297v4
2018-12-21,Structural and Magnetic Characterization of Spin Canted Mixed Ferrite-Cobaltites: LnFe0.5Co0.5O3 (Ln = Eu and Dy),"The mixed ferrite-cobaltites LnFe0.5Co0.5O3, with Ln = Eu & Dy have been
prepared by a sol-gel method and the samples have been characterized using
X-ray diffraction and electron microscopy. The magnetic investigations reveal
that both samples ordered in canted antiferromagnetic structures near room
temperature. The Dzyaloshinskii-Moriya or antisymmetric exchange interaction
induces weak ferromagnetism due to canting of the antiferromagnetically ordered
spins. In the case of Ln-Fe-Co orthoferrites, two magnetic sublattices (Ln3+-4f
and Fe3+/Co3+-3d) generally align in opposite directions and interesting
temperature dependent phenomena: e.g. uncompensated antiferromagnetic
sublattices and spin-reorientations, are observed in the system. The existence
of hysteresis at low temperature region has been explained in terms of the
strength of magnetic interactions between Fe3+ and Co3+ ions with different
A-site rare earth cations.",1812.09031v2
2019-02-19,Magnetic interaction and anisotropy axes arrangement in nanoparticle aggregates can enhance or reduce the effective magnetic anisotropy,"The magnetic response of nanostructures plays an important role on biomedical
applications being strongly influenced by the magnetic anisotropy. In this work
we investigate the role of temperature, particle concentration and nanoparticle
arrangement forming aggregates in the effective magnetic anisotropy of Mn-Zn
ferrite-based nanoparticles. Electron magnetic resonance and coercivity
temperature dependence analyses, were critically compared for the estimation of
the anisotropy. We found that the temperature dependence of the anisotropy
follows the Callen-Callen model, while the symmetry depends on the particle
concentration. At low concentration one observes only an uniaxial term, while
increasing a cubic contribution has to be added. The effective anisotropy was
found to increase the higher the particle concentration on magnetic colloids,
as long as the easy axis was at the same direction of the nanoparticle chain.
Increasing even further the concentration up to a highly packed condition
(powder sample) one observes a decrease of the anisotropy, that was attributed
to the random anisotropy axes configuration.",1902.07188v1
2019-08-07,Tunability of Room Temperature Ferromagnetism in Spintronic Semiconductors through Non-magnetic Atoms,"The implementation and control of room temperature ferromagnetism (RTFM) by
adding magnetic atoms to a semiconductor's lattice has been one of the most
important problems in solid state state physics in the last decade. Herein we
report for the first time, to our knowledge, on the mechanism that allows RTFM
to be tuned by the inclusion of \emph{non-magnetic} aluminum in nickel ferrite.
This material, NiFe$_{2-x}$Al$_x$O$_4$ (x=0, 0.5, 1.5), has already shown much
promise for magnetic semiconductor technologies, and we are able to add to its
versatility technological viability with our results. The site occupancies and
valencies of Fe atoms (Fe$^{3+}$ T$_d$, Fe$^{2+}$ O$_h$, and Fe$^{3+}$ O$_h$)
can be methodically controlled by including aluminum. Using the fact that
aluminum strongly prefers a 3+ octahedral environment, we can selectively fill
iron sites with aluminum atoms, and hence specifically tune the magnetic
contributions for each of the iron sites, and therefore the bulk material as
well. Interestingly, the influence of the aluminum is weak on the electronic
structure (supplemental material), allowing one to retain the desirable
electronic properties while achieving desirable magnetic properties.",1908.02610v1
2019-08-14,A Tuneable Magnetic Domain Wall Conduit Regulating Nanoparticle Diffusion,"We demonstrate a general and robust method to confine on a plane strongly
diffusing submicrometer particles in water by using size tunable magnetic
channels. These virtual conduits are realized with pairs of movable Bloch walls
(BWs) located within an epitaxially grown ferrite garnet film. We show that,
once inside the magnetic conduit, the particles experience an effective local
parabolic potential in the transverse direction, while freely diffusing along
the conduit. The stiffness of the magnetic potential is determined as a
function of field amplitude which varies the width of the magnetic channel, and
precise control of the degree of confinement is demonstrated by tuning the
applied field. The magnetic conduit is then used to realize single files of
non-passing particles and to induce periodic condensation of an ensemble of
particles into parallel stripes in a completely controllable and reversible
manner.",1908.05039v1
2019-08-20,"Design of a High Strength, High Ductility 12 wt% Mn Medium Manganese Steel With Hierarchical Deformation Behaviour","A novel medium Mn steel of composition Fe-12Mn-4.8Al-2Si-0.32C-0.3V was
manufactured with 1.09 GPa yield strength, 1.26 GPa tensile strength and 54%
elongation. The thermomechanical process route was designed to be industrially
translatable and consists of hot and then warm rolling before a 30 min
intercritical anneal. The resulting microstructure comprised of coarse
elongated austenite grains in the rolling direction surrounded by necklace
layers of fine austenite and ferrite grains. The tensile behaviour was
investigated by in-situ neutron diffraction and the evolution of microstructure
studied with Electron Backscattered Diffraction (EBSD). It was found that the
coarse austenite grains contributed to the first stage of strain hardening by
transforming into martensite and the fine austenite necklace grains contributed
to the second stage of strain hardening by a mixture of twinning and
transformation induced plasticity (TWIP and TRIP) mechanisms. This hierarchical
deformation behaviour contributed to the exceptional ductility of this steel.",1908.07258v3
2019-11-08,First principles calculation of shift current in chalcopyrite semiconductor ZnSnP$_2$,"The bulk photovoltaic effect generates intrinsic photocurrents in materials
without inversion symmetry. Shift current is one of the bulk photovoltaic
phenomena related to the Berry phase of the constituting electronic bands:
photo-excited carriers coherently shift in real space due to the difference in
the Berry connection between the valence and conduction bands. Ferroelectric
semiconductors and Weyl semimetals are known to exhibit such nonlinear optical
phenomena. Here we consider chalcopyrite semiconductor ZnSnP$_2$ which lacks
inversion symmetry and calculate the shift current conductivity. We find that
the magnitude of the shift current is comparable to the recently measured
values on other ferroelectric semiconductors and an order of magnitude larger
than bismuth ferrite. The peak response for both optical and shift current
conductivity, which mainly comes from P-3$p$ and Sn-5$p$ orbitals, is several
eV above the bandgap.",1911.03376v2
2019-11-20,Polymer-bonded anisotropic SrFe$_\text{12}$O$_\text{19}$ filaments for fused filament fabrication,"In this publication we describe the extrusion process and the properties of
polymer-bonded anisotropic SrFe$_\text{12}$O$_\text{19}$ filaments for fused
filament fabrication (FFF). Highly filled polyamide 12 filaments with a filling
fraction from 40 vol.% to 55 vol.% are mixed and extruded into filaments with a
diameter of 1.75 mm. Such filaments are processable with a conventional FFF 3D
printer. No modifications of the 3D printer are necessary. Detailed mechanical
and magnetic investigations of printed samples are performed and discussed. In
the presence of an external alignment field, the Sr ferrite particles inside
the PA12 matrix can be aligned along an external magnetic field. The remanence
can be increased by 40 % by printing anisotropic structures. For the 55 vol.%
filled filament, a remanence of 212.8 mT and a coercivity of 307.4 mT are
measured. The capabilities of printing magnetic anisotropic structures in a
complex external field are presented with a Halbach-array arrangement. By the
aim of an inverse field model, based on a finite element method, the
orientation of the particles and the quality of the print can be estimated by a
nondestructive method.",1911.08869v1
2019-12-09,Optical vortex-induced forward mass transfer: Manifestation of helical trajectory of optical vortex,"The orbital angular momentum of an optical vortex field is found to twist
high viscosity donor material to form a micron-scale 'spin jet'. This unique
phenomenon manifests the helical trajectory of the optical vortex. Going beyond
both the conventional ink jet and laser induced forward mass transfer (LIFT)
patterning technologies, it also offers the formation and ejection of a
micron-scale 'spin jet' of the donor material even with an ultrahigh viscosity
of 4 Pas. This optical vortex laser induced forward mass transfer (OV-LIFT)
patterning technique will enable the development of next generation printed
photonic/electric/spintronic circuits formed of ultrahigh viscosity donor dots
containing functional nanoparticles, such as quantum dots, metallic particles
and magnetic ferrite particles, with ultrahigh spatial resolution. It can also
potentially explore a completely new needleless drug injection.",1912.03907v1
2019-12-16,3D printing of polymer-bonded anisotropic magnets in an external magnetic field and by a modified production process,"The possibility of producing polymer-bonded magnets with the aid of additive
processes, such as 3D printing, opens up a multitude of new areas of
application. Almost any structures and prototypes can be produced
cost-effectively in small quantities. Extending the 3D printing process allows
the manufacturing of anisotropic magnetic structures by aligning the magnetic
easy axis of ferromagnetic particles inside a paste-like compound material
along an external magnetic field. This is achieved by two different approaches:
First, the magnetic field for aligning the particles is provided by a permanent
magnet. Secondly, the 3D printing process itselfs generates an anisotropic
behavior of the structures. An inexpensive and customizable end-user fused
filament fabrication 3D printer is used to print the magnetic samples. The
magnetical properties of different magnetic anisotropic Sr ferrite and SmFeN
materials are investigated and discussed.",1912.07374v1
2020-05-12,Magnetically induced topological transitions of hyperbolic dispersion in biaxial gyrotropic media,"Magnetically induced topological transitions of isofrequency surfaces of bulk
waves propagating through an unbounded biaxial gyrotropic medium are studied.
The medium is constructed from a two-component superlattice composed of
magnetized ferrite and semiconductor layers. To derive the constitutive
parameters of the gyrotropic medium, a homogenization procedure from the
effective medium theory is applied. The study is carried out in the frequency
range near the frequency of ferromagnetic resonance, where the magnetic
subsystem possesses the properties of natural hyperbolic dispersion. The
topological transitions from an open type-I hyperboloid to several intricate
hyperbolic-like forms are demonstrated for the extraordinary waves. We reveal
how realistic material losses change the form of isofrequency surface
characterizing hyperbolic dispersion. The obtained results broaden our
knowledge on the possible topologies of isofrequency surfaces that can appear
in gyrotropic media influenced by an external static magnetic field.",2005.05875v1
2021-02-13,Highly efficient parallel grand canonical simulations of interstitial-driven deformation-diffusion processes,"Diffusion of interstitial alloying elements like H, O, C, and N in metals and
their continuous relocation and interactions with their microstructures have
crucial influences on metals properties. However, besides limitations in
experimental tools in capturing these mechanisms, the inefficiency of numerical
tools also inhibits modeling efforts. Here, we present an efficient framework
to perform hybrid grand canonical Monte Carlo and molecular dynamics
simulations that allow for parallel insertion/deletion of Monte Carlo moves. A
new methodology for calculation of the energy difference at trial moves that
can be applied to many-body potentials as well as pair ones is a primary
feature of our implementation. We study H diffusion in Fe (ferrite phase) and
Ni polycrystalline samples to demonstrate the efficiency and scalability of the
algorithm and its application. The computational cost of using our framework
for half a million atoms is a factor of 250 less than the cost of using
existing libraries.",2102.06980v1
2021-02-15,Patterning enhanced tetragonality in BiFeO3 thin films with effective negative pressure by helium implantation,"Helium implantation in epitaxial thin films is a way to control the
out-of-plane deformation independently from the in-plane strain controlled by
epitaxy. In particular, implantation by means of a helium microscope allows for
local implantation and patterning down to the nanometer resolution, which is of
interest for device applications. We present here a study of bismuth ferrite
(BiFeO3) films where strain was patterned locally by helium implantation. Our
combined Raman, XRD and TEM study shows that the implantation causes an
elongation of the BiFeO3 unit cell and ultimately a transition towards the
so-called super-tetragonal polymorph via states with mixed phases. In addition,
TEM reveals the onset of amorphization at a threshold dose that does not seem
to impede the overall increase in tetragonality. The phase transition from the
R-like to T-like BiFeO3 appears as first-order in character, with regions of
phase coexistence and abrupt changes in lattice parameters.",2102.07557v1
2021-02-16,Magnetic phase diagram of rare-earth orthorhombic perovskite oxides,"Spin reorientation and magnetisation reversal are two important features of
the rare-earth orthorhombic provskites ($RM$O$_{3}$'s) that have attracted a
lot of attention, though their exact microscopic origin has eluded researchers.
Here, using density functional theory and classical atomistic spin dynamics we
build a general Heisenberg magnetic model that allows to explore the whole
phase diagram of the chromite and ferrite compounds and to scrutinize the
microscopic mechanism responsible for spin reorientations and magnetisation
reversals. We show that the occurrence of a magnetization reversal transition
depends on the relative strength and sign of two interactions between
rare-earth and transition-metal atoms: superexchange and Dzyaloshinsky-Moriya.
We also conclude that the presence of a smooth spin reorientation transition
between the so-called $\Gamma_4$ and the $\Gamma_2$ phases through a coexisting
region, and the temperature range in which it occurs, depends on subtle balance
of metal--metal (superexchange and Dzyaloshinsky-Moriya) and metal--rare-earth
(Dzyaloshinsky-Moriya) couplings. In particular, we show that the intermediate
coexistence region occurs because the spin sublattices rotate at different
rates.",2102.08152v1
2021-03-03,Operating a passive on-chip superconducting circulator: device control and quasiparticle effects,"Microwave circulators play an important role in quantum technology based on
superconducting circuits. The conventional circulator design, which employs
ferrite materials, is bulky and involves strong magnetic fields, rendering it
unsuitable for integration on superconducting chips. One promising design for
an on-chip superconducting circulator is based on a passive Josephson-junction
ring. In this paper, we consider two operational issues for such a device:
circuit tuning and the effects of quasiparticle tunneling. We compute the
scattering matrix using adiabatic elimination and derive the parameter
constraints to achieve optimal circulation. We then numerically optimize the
circulator performance over the full set of external control parameters,
including gate voltages and flux bias, to demonstrate that this
multi-dimensional optimization converges quickly to find optimal working
points. We also consider the possibility of quasiparticle tunneling in the
circulator ring and how it affects signal circulation. Our results form the
basis for practical operation of a passive on-chip superconducting circulator
made from a ring of Josephson junctions.",2103.02759v2
2021-03-09,Specific loss power of magnetic nanoparticles (fluid) hyperthermia in non-adiabatic conditions,"We investigate the magnetic nanoparticles (fluid) hyperthermia in
non-adiabatic conditions through the calorimetric method. Specifically, we
propose a theoretical approach to magnetic hyperthermia from a thermodynamic
point of view. To test the robustness of the approach, we perform hyperthermia
experiments and analyze the thermal behavior of magnetite and magnesium ferrite
magnetic nanoparticles dispersed in water submitted to an alternating magnetic
field. From our findings, besides estimating the specific loss power value from
a non-adiabatic process, thus enhancing the accuracy in the determination of
this quantity, we provide physical meaning to parameters found in literature
that still remained not fully understood, and bring to light how they can be
obtained experimentally.",2103.05691v1
2021-03-22,Spin-dependent optical excitations in LiFeO2,"The three-dimensional ternary LiFeO2 compound presents various unusual
essential properties. The main features are thoroughly explored by the density
functional and many-body perturbation theory. The concise physical/chemical
picture, the critical spin-polarizations and orbital hybridizations in the Li-O
and Fe-O bonds, are clearly examined through geometric optimization,
quasi-particle energy spectra, spin-polarized density of states, the spatial
charge densities, the spin-density distributions, and the strong optical
responses. The unusual optical transitions cover various frequency-dependent
absorption structures, and the most prominent plasmon modes are identified by
the dielectric functions, energy loss functions, reflectance spectra, and
absorption coefficients. Optical excitations are anisotropic and strongly
affected by excitonic effects. The close combinations of electronic, magnetic
and optical properties allow us to identify the significant spin-polarizations
and orbital hybridizations for each available excitation channel. The lithium
ferrite compound can be used for spintronic and photo-catalysis applications.",2103.11838v3
2021-03-31,Slip band interactions and GND latent hardening in a galling resistant stainless steel,"Slip activation, slip band interactions, and GND densities in iron-base,
galling resistant alloy Nitronic 60 have been characterised at the grain length
scale using small-scale mechanical testing with high resolution digital image
correlation and high-angular resolution electron backscatter diffraction. By
correlating the two measurement techniques, new insight into slip band
interactions, the generation of lattice curvature and the corresponding
accumulation of geometrically necessary dislocations (GNDs) is provided.
Multiple discrete slip bands are typically active within single grains,
resulting in significant slip band interactions. Crossing slip bands were found
to generate accumulations of GNDs. Regions where slip bands block other slip
bands were associated with the highest GND densities, in excess of three time
the densities of crossing slip bands. Representative crystal plasticity
modelling investigations have demonstrated that discrete slip blocking events
are responsible for locally elevated GND density. This behaviour is
rationalised in terms of lattice curvature associated with the differing levels
of constraint provided by the crossing or blocking-type behaviours. Ferrite
grains are also found to contribute to the generation of GNDs. Together, these
two effects provide significant work hardening mechanisms, likely to be key to
the development of future iron-base hard facing alloys.",2103.16864v1
2021-04-01,Missing level statistics in a dissipative microwave resonator with partially violated time-reversal invariance,"We report on the experimental investigation of the fluctuation properties in
the resonance frequency spectra of a flat resonator simulating a dissipative
quantum billiard subject to partial time-reversal invariance violation (TIV)
which is induced by two magnetized ferrites. The cavity has the shape of a
quarter bowtie billiard of which the corresponding classical dynamics is
chaotic. Due to dissipation it is impossible to identify a complete list of
resonance frequencies. Based on a random-matrix theory approach we derive
analytical expressions for statistical measures of short- and long-range
correlations in such incomplete spectra interpolating between the cases of
preserved time-reversal invariance and complete TIV and demonstrate their
applicability to the experimental spectra.",2104.02572v1
2021-04-20,Magnetic dipolar modes in magnon-polariton condensates,"For dipole-carrying excitations observed in a high-quality resonator,
strong-coupling modes can appear as composite bosons with the spontaneous
formation of quantized vortices in the condensed phase of a polariton fluid. In
exciton-polaritons, in particular, it leads to sustained trapping of the
emitted photon. In this paper, we show that magnon-polaritons can be realized
due to magnon condensation caused by magnetic dipole-dipole interaction. In a
quasi-2D ferrite disk placed in a microwave cavity, one observes quantum
confinement effects of magnetic-dipolar-mode (MDM) oscillations. These modes,
characterized by energy eigenstates with rotational superflows and quantized
vortices, are exhibited as spinor condensates. Along with the condensation of
MDM magnons in the quasi-2D disk of the magnetic insulator, electric dipole
condensation is also observed. At the MDM resonances, transfer between angular
momenta in the magnetic insulator and in the vacuum cavity, demonstrates
generation of vortex flows with fixed handedness. This indicates unique
topological properties of polariton wavefronts. One observes curved wavefronts
and effects of supperradiance in microwave structures. In an environment of
scattering states of microwave waveguide, EM waves can carry the topological
phases of MDM resonances.",2104.10048v1
2021-05-06,Interfacial strain relief by periodic dislocation doublets emerging from rotationally related orientation relationships of Y4Zr3O12 dispersions in ferrite matrix,"The trigonal/bcc orientation relationships (ORs) and their likelihood of
occurrence are extensively studied using dispersed Y4Zr3O12nano-precipitates in
bcc Fe matrix by means of transmission electron microscopy, image simulations,
and a crystallographic model. Two orientation relationships related by a
rotation:[1-20]||[111] with (21-2)||(-110) and [1-20]||[111] with
(00-3)||(-110), are established and periodic arrays of misfit dislocation
doublets are identified at the strained interface in (110) for both ORs.
Further eighteen energetically feasible ORs in Y4Zr3O12/bcc system are deduced
by combining stereographic projections, which include the two predominant ORs
in this study and other ORs in literature. The orientation relationship which
generates the interface with a minimum number of dislocation doublets is the
most frequent.",2105.02530v1
2021-05-27,Pushing the Study of Point Defects in Thin Film Ferrites to Low Temperatures Using In Situ Ellipsometry,"Unveiling point defects concentration in transition metal oxide thin films is
essential to understand and eventually control their functional properties,
employed in an increasing number of applications and devices. Despite this
unquestionable interest, there is a lack of available experimental techniques
able to estimate the defect chemistry and equilibrium constants in such oxides
at intermediate-to-low temperatures. In this study, the defect chemistry of a
relevant material such as La1-xSrxFeO3-d (LSF) with (x = 0.2, 0.4 and 0.5
(LSF20, LSF40 and LSF50 respectively) is obtained by using a novel in situ
spectroscopic ellipsometry approach applied to thin films. Through this
technique, the concentration of holes in LSF is correlated to measured optical
properties and its evolution with temperature and oxygen partial pressure is
determined. In this way, a systematic description of defect chemistry in LSF
thin films in the temperature range from 350dC to 500dC is obtained for the
first time, which represents a step forward in the understanding of LSF20,
LSF40 and LSF50 for emerging low temperature applications.",2105.13039v1
2021-05-31,Effect of Zr and Al Addition on Nanocluster Formation in Oxide Dispersion Strenghthened Steel-an ab initio Study,"Conventional Oxide dispersion strengthened steels are characterized by
thermally stable, high density of Y-Ti-O nanoclusters, which are responsible
for their high creep strength. Ti plays a major role in obtaining a high
density of ultrafine particles of optimum size range of 2-10 nm. In
Al-containing ODS steels developed for corrosion resistance, Y-Al-O clusters
formed are of size range 20 -100 nm, and Ti fails in making dispersions finer
in the presence of Al. Usage of similar alloying elements like Zr in place of
Ti is widely considered. In this study, binding energies of different stages of
Y-Zr-O-Vacancy and Y-Al-O-Vacancy complexes in the bcc Iron matrix are studied
by first-principle calculations. It is shown that in all the stages of
formation, Y-Zr-O-Vacancy clusters have higher binding energy than
Y-Al-O-Vacancy clusters and hence in ferritic steel containing both Zr and Al,
Y-Zr-O-Vacancy clusters are more stable and more favored to nucleate than
Y-Al-O-Vacancy clusters. The bonding nature in each stage is analyzed using
charge density difference plots for the plausible reason for higher stability
of Y-Zr-O-Vacancy clusters.",2105.15063v1
2021-06-24,Chiral Quantum Network with Giant Atoms,"In superconducting quantum circuits (SQCs), chiral routing quantum
information is often realized with the ferrite circulators, which are usually
bulky, lossy and require strong magnetic fields. To overcome those problems, we
propose a novel method to realize chiral quantum networks by exploiting giant
atom effects in SQC platforms. By assuming each coupling point being modulated
with time, the interaction becomes momentum-dependent, and giant atoms will
chirally emit photons due to interference effects. The chiral factor can
approach 1, and both the emission direction and rate can be freely tuned by the
modulating signals. We demonstrate that a high-fidelity state transfer between
remote giant atoms can be realized. Our proposal can be integrated on the
superconducting chip easily, and has the potential to work as a tunable toolbox
for quantum information processing in future chiral quantum networks.",2106.13187v3
2021-06-23,Highly Linear Nonmagnetic Circulator Enabled By A Temporal Nonreciprocal Phase Shifter,"Conventional circulators are made of magnetic ferrites and suffer from a
cumbersome architecture, incompatibility with integrated circuit technology and
inability for high frequency applications. To overcome these limitations, here
we propose a lightweight low-profile non-magnetic circulator comprising a
nonreciprocal time-varying phase shifter. This circulator is composing a
nonreciprocal temporal phase shifter and two reciprocal delay-line-based phase
shifters. The proposed nonreciprocal temporal phase shifter is based on the
generation of time-harmonic signals, enforcing destructive interference for
undesired time harmonics and constructive interference for desired time
harmonics at different locations of the structure. Such a unique task is
accomplished through two phase-engineered temporal loops. The phase and
frequency of these two loops are governed by external signals with different
phases, imparting an effective electronic angular momentum to the system. We
observe large isolation level of greater than 32 dB, a P1dB of +31.7 dBm and
IIP3 of +42.4 dBm. Furthermore, this circulator is endowed with a
reconfigurable architecture and can be directly embedded in a conventional
integrated circuit (IC) technology to realize a class of high power handling
and linear IC circulators.",2107.09788v1
2021-07-21,Spin orbit torque switching of antiferromagnet through the Neel reorientation in rare-earth ferrite,"We suggest coherent switching of canted antiferromagnetic (AFM) spins using
spin-orbit torque (SOT) in small magnet. The magnetic system of orthoferrite
features biaxial easy anisotropy and the Dzyaloshinskii Moriya interaction,
which is perpendicular to the easy axes and therefore creates weak
magnetization (m). A damping-like component of the SOT induces N\'eel
reorientation along one of the easy axes and then exerts torque on m, leading
to tilting of the N\'eel order l. The torque on the magnetization becomes
stronger due to coupling with the induced Oersted field or the field-like
component of the SOT, enhancing the tilting of l. Therefore, l is found to
experience deterministic switching after the SOT is turned off. Based upon both
numerical and analytical analysis of the coherent switching, XOR logic gates
are also found to be implemented in a single magnetic layer. In addition, we
investigate how magnetic parameters affect the critical reorientation angle and
current density in a simple layered structure of platinum and a canted AFM. Our
findings are expected to provide an alternative spin-switching mechanism for
ultrafast applications such as spin logic and electronic devices.",2107.10156v1
2021-09-09,Identification of object composition with Magnetic Inductive Tomography,"The inductive response of an object to an oscillating magnetic field reveals
information about its electrical conductivity and magnetic permeability. Here
we introduce a technique that uses measurements of the angular, frequency and
spatial dependence of the inductive signal to determine object composition.
Identification is performed by referencing an object's inductive response to
that of materials with mutually exclusive properties such as copper (high
electric conductivity, negligible magnetic permeability) and ferrite
(negligible electric conductivity, high magnetic permeability). The technique
uses a sensor with anisotropic sensitivity to discriminate between the
different characters of the eddy current and magnetisation driven object
responses. Experimental validation of the method is performed through Magnetic
Induction Tomography measurement with a radio-frequency atomic magnetometer.
Possible applications of the technique in security screening devices are
discussed.",2109.04074v1
2021-11-02,Anti-PT-symmetry-enhanced interconversion between microwave and optical fields,"The intrinsic dissipation of systems into a shared reservoir introduces
coherence between two systems, enabling anti-Parity-Time (anti-PT) symmetry. In
this paper, we propose an anti-PT symmetric converter, consisting of a
microwave cavity coupled dissipatively to a ferromagnetic sphere, which
supports significant improvements in the conversion efficiency when compared to
coherently coupled setups. In particular, when only the ferrite sample is
driven, the strong coherence induced by the vacuum of the mediating channel
leads to much stronger enhancements in the intended conversion. The enhancement
is an inalienable artifact of the emergence of a long-lived, dark mode
associated with a quasi-real singularity of the hybrid system. In addition, we
observe considerable asymmetry in the efficiencies of microwave-to-optical and
optical-to-microwave conversions, in spite of the symmetrical structure of the
trilinear optomagnonic coupling stimulating both the transduction phenomena.
The nonreciprocity stems from the intrinsic asymmetry in the couplings of the
microwave and optical fields to the cavity-magnon network as well as the phase
coupling entailed by the spatial separation.",2111.01335v1
2021-11-26,Deep Learning for automated phase segmentation in EBSD maps. A case study in Dual Phase steel microstructures,"Electron Backscattering Diffraction (EBSD) provides important information to
discriminate phase transformation products in steels. This task is
conventionally performed by an expert, who carries a high degree of
subjectivity and requires time and effort. In this paper, we question if
Convolutional Neural Networks (CNNs) are able to extract meaningful features
from EBSD-based data in order to automatically classify the present phases
within a steel microstructure. The selected case of study is ferrite-martensite
discrimination and U-Net has been selected as the network architecture to work
with. Pixel-wise accuracies around ~95% have been obtained when inputting raw
orientation data, while ~98% has been reached with orientation-derived
parameters such as Kernel Average Misorientation (KAM) or pattern quality.
Compared to other available approaches in the literature for phase
discrimination, the models presented here provided higher accuracies in shorter
times. These promising results open a possibility to work on more complex steel
microstructures.",2112.03072v1
2021-12-08,Micromechanical fatigue experiments for validation of microstructure-sensitive fatigue simulation models,"Crack initiation governs high cycle fatigue life and is susceptible to
microstructural details. While corresponding microstructure-sensitive models
are available, their validation is difficult. We propose a validation framework
where a fatigue test is mimicked in a sub-modeling simulation by embedding the
measured microstructure into the specimen geometry and adopting the
experimental boundary conditions. Exemplary, a phenomenological crystal
plasticity model was applied to predict deformation in ferritic steel
(EN1.4003). Hotspots in commonly used fatigue indicator parameter maps are
compared with damage segmented from micrographs. Along with the data, the
framework is published for benchmarking future micromechanical fatigue models.",2112.04342v1
2021-12-31,Tunable magnetic field source for magnetic field imaging microscopy,"In this work we present a novel, compact, power efficient magnetic field
source design for magnetic field imaging microscopy. The device is based on a
pair of diametrically magnetized permanent magnet cylinders with
electro-mechanical rotation control and ferrite field concentrators. A Hall
probe and NV centers in diamond are used to demonstrate a proof of concept of a
proposed magnetic field setup and to characterise the homogeneity of the
produced magnetic field on a micrometer scale. Numerical simulation results are
compared with experimental results showing good agreement of the distribution
of the magnetic field in the setup. As a result, a magnetic field source with a
tunable field amplitude in the range from 1 mT to 222 mT is demonstrated,
achieving a magnetic field homogeneity of 2 ppm/$\mu$m or 0.5 $\mu$T/$\mu$m at
222 mT in a 25$\times$25 $\mu$m field of view.",2112.15359v1
2022-01-02,Symmetry analysis of magnetoelectric effects in perovskite-based multiferroics,"In this article, we perform the symmetry analysis of perovskite-based
multiferroics: bismuth ferrite (BiFeO3)-like, orthochromites (RCrO3), and
Ruddlesden-Popper perovskites (Ca3Mn2O7-like), being the typical
representatives of multiferroics of the trigonal, rhombic, and tetragonal
crystal families and explore the effect of crystallographic distortions on
magnetoelectric properties. We determine the principal order parameters for
each of the considered structures and obtain their invariant combinations
consistent with the particular symmetry. This approach allowed us to analyze
the features of the magnetoelectric effect observed during structural phase
transitions in BixR1-xFeO3 compounds and show that the rare-earth sublattice
gives an impact into the linear magnetoelectric effect allowed by the symmetry
of the new structure. It is shown that the magnetoelectric properties of
ortho-chromites are attributed to the couplings between the magnetic and
electric dipole moments arising near Cr3+ ions due to distortions linked with
rotations and deformations of the CrO6 octahedra. For the first time, such
symmetry consideration was implemented in the analysis of the Ruddlesden-Popper
structures, which demonstrates the possibility of realizing the magnetoelectric
effect in the Ruddlesden-Popper phases containing magnetically active cations
and allows to estimate conditions required for its optimization.",2201.00316v1
2022-01-25,Stability and low-energy orientations of interphase boundaries in multiaxial ferroelectrics: Phase-field simulations,"The coexistence of different ferroelectric phases enables the tunability of
the macroscopic properties and extensive applications from piezoelectric
transducers to nonvolatile memories. Here we develop a thermodynamic model to
predict the stability and low-energy orientations of boundaries between
different phases in ferroelectrics. Taking lead zirconate titanate and bismuth
ferrite as two examples, we demonstrate that the low-energy orientations of
interphase boundaries are largely determined by minimizing the electrostatic
and elastic energies. Phase-field simulations are employed to analyze the
competition between the interfacial energy and the electrostatic and elastic
energies. Our simulation results demonstrate that the lowering of crystal
symmetry could occur due to the electrical and mechanical incompatibilities
between the two phases, which can be used to explain the experimentally
observed low-symmetry phases near morphotropic phase boundaries. Our work
provides theoretical foundations for understanding and controlling the
interphase boundaries in ferroelectric materials for multifunctional
applications.",2201.10074v1
2022-02-13,Kinetic Monte Carlo modelling of Helium Bubble Nucleation onto Oxides in the Fe-Ti-Y-O System,"A Kinetic Monte Carlo (KMC) model was created to simulate the insertion of
transmutation He atoms into nanostructured ferritic alloys (NFAs) under neutron
irradiation. Interstitial He atoms migrate through the NFA until becoming
trapped in bubbles of other He atoms and vacancies created from irradiation.
The Y-Ti-O nano-oxides in the NFAs were found to be effective in capturing
these He atoms and preventing bubbles from forming at the grain boundary and
appear to replicate the characteristics (size and number density) observed in
other experiments. The bubbles were found to prefer the <111> oxide interface
as a nucleation site and the stable bubbles have a He/Vac ratio between 1.3 and
1.8 He/Vac. The influence of He bubbles on the segregation of solutes to the
grain boundaries or on the stability of the nano-oxides were negligible.",2202.06189v1
2022-03-08,Coupling between improper ferroelectricity and ferrimagnetism in hexagonal ferrites,"Antisymmetric Dzyaloshinskii-Moriya (DM) interactions generating from the
spin-orbit coupling induce various fascinating properties, like magnetoelectric
(ME) effect, weak ferromagnetism and non-trivial topological spin textures like
skyrmions, in real materials. Compared to their symmetric isotropic exchange
counterpart, these interactions are generally of a weaker order of strength,
creating modest twisting in the spin structure which results in weak
ferromagntism or weak linear ME effect. Our proposed two-sublattice model, in
contrast, predicts a hitherto unobserved, charge ordered non-collinear
ferrimagnetic behavior with a considerably high magnetization $\textbf{M}$
coexisting with a ferroelectric (FE) order with an electric polarization
$\textbf{P}$ and a strong cross coupling between them which is primarily driven
by the inter-sublattice DM interactions. The key to realize these effects is
the coupling between these microscopic interactions and the FE primary order
parameter. We predict microscopic mechanisms to achieve electric field
$\textbf{E}$ induced spin-reorientation transitions and 180$^{\circ}$ switching
of the direction of $\textbf{M}$. This model was realized in the hexagonal
phase of LuFeO$_3$ doped with electrons. This system shows $P \sim$ 15
$\mu$C/cm$^2$, $M \sim$ 1.3 $\mu_B$/Fe and magnetic transition near room
temperature ($\sim$ 290 K). Our theoretical results are expected to stimulate
further quest for energy-efficient routes to control magnetism for spintronics
applications.",2203.03841v1
2022-04-20,Ferroelectricity and topological vortices from molecular ordering in metal-organic frameworks,"Metal-organic frameworks comprehend a wide class of hybrid organic-inorganic
materials with general structure A$_m$BX$_n$, with $A$ and $X$ being organic
molecules and B a metal cation. This often results in enhanced structural
flexibility and new functionalities. Hybrid perovskites ABX$_3$ are a
well-known example.} In an Iron-based perovskites, (DMA)Fe^{II-III}(COOH)_3,
dimethylammonium (DMA) molecules are organized in a hexagonal structure. They
are orientationally disordered at high temperatures, but order at around
$T=100$~K in a peculiar toroidal pattern. Recent experimental and theoretical
study suggest the appearance of ferroelectric polarization in this phase,
although the measured polarization is small, and the mechanism of
ferroelectricity is still debated. We formulate a Landau-type theory that
clarifies the connection between the electric polarization, molecular pattern,
and distortive modes of the inorganic lattice. We find a remarkable mechanism
of improper ferroelectricity, analogue to the trimerization process in
inorganic hexagonal ferrites and manganites, but here driven by the ordering of
organic molecules in a metal-organic framework. Our study reveals an extremely
rich phase diagram with the prediction of topological domain walls, where the
ferroelectricity arise from tripling the unit cells due to molecular ordering.
Wide domain walls with inner structure are predicted.",2204.09546v1
2022-06-21,An iterative method for reference pattern selection in high resolution electron backscatter diffraction (HR-EBSD),"For high (angular) resolution electron backscatter diffraction (HR-EBSD), the
selection of a reference diffraction pattern (EBSP0) significantly affects the
precision of the calculated strain and rotation maps. This effect was
demonstrated in plastically deformed body-centred cubic and face-centred cubic
ductile metals (ferrite and austenite grains in duplex stainless steel) and
brittle single-crystal silicon, which showed that the effect is not only
limited to measurement magnitude but also spatial distribution. An empirical
relationship was then identified between the cross-correlation parameter and
angular error, which was used in an iterative algorithm to identify the optimal
reference pattern that maximises the precision of HR-EBSD.",2206.10242v2
2022-12-13,Logarithmic wave-mechanical effects in polycrystalline metals: Theory and experiment,"Schrodinger-type wave equations with logarithmic nonlinearity occur in
hydrodynamic models of Korteweg-type materials with capillarity and surface
tension, which can undergo liquid-solid or liquid-gas phase transitions. One of
the predictions of the theory is a periodic pattern of density inhomogeneities
occurring in the form of either bubbles (topological phase), or cells
(non-topological phase). Such inhomogeneities are described by solitonic
solutions of a logarithmic wave equation, gaussons and kinks, in the vicinity
of the liquid-solid phase transition. During the solidification process, these
inhomogeneities become centers of nucleation, thus shaping the polycrystalline
structure of the metal grains. The theory predicts a Gaussian profile of
material density inside such a cell, which should manifest in a Gaussian-like
profile of microhardness inside a grain. We report experimental evidence of
large-scale periodicity in the structure of grains in the ferrite steel
S235/A570, copper C-Cu/C14200, austenite in steel X10CrNiTi18-10/AISI 321, and
aluminium-magnesium alloy 5083/5056; and also Gaussian-like profiles of
microhardness inside an averaged grain in these materials.",2212.06407v1
2023-01-04,Diameter and Aggregation Controlled Preparation by Solvothermal Synthesis of Ultra-small Particles CuFe$_2$O$_4$,"Copper ferrite nanoparticles have catalytic activity for hydrogen peroxide,
which can be used in many fields. This characteristic comes from the physical
properties of matters at nanometer scale. Thus, controlling the size and
aggregation of nanoparticles during the synthesis is one of the ways to obtain
target performance. In this article, a kind of ultra-small nano particle
CuFe$_2$O$_4$ with uniform morphology was prepared by solvothermal synthesis.
The effects of solvent, reactant molar ratio, reaction temperature, surfactant
and reaction time on the yield of CuFe$_2$O$_4$, size and morphology of nano
particles were investigated under different synthesis conditions. XRD, TEM, EDS
were used to analysis the materials, and the physical properties of the
products were analyzed. An optimized solvothermal synthesis scheme was
proposed.",2301.01658v2
2023-01-21,Hard Ferromagnets as a New Perspective on Materials for Thermomagnetic Power Generation Cycles,"We consider the ways in which magnetically hard materials can be used as the
working materials in thermomagnetic power generation (TMG) cycles in order to
expand the area in the magnetisation vs. applied field ($M-H$) plane available
for energy conversion. There are 3 parts to this Perspective. First,
experiments on commercially available hard ferrites reveal that, while these
materials are not yet good TMG candidates, hard ferromagnets with higher
thermal conductivity and a greater change of magnetization with temperature
could outperform existing TMG materials. Second, computational results indicate
that biasing a soft magnet with a hard ferromagnet is essentially equivalent to
shifting the $M-H$ loop by an amount proportional to the field of the biasing
magnet. Work outputs under biased conditions show a substantial improvement
over unbiased cycles, but experimental verification is needed. Third, we
discuss the rationale for exploring artificial spin reorientation materials as
novel TMG working materials.",2301.08854v1
2023-01-21,Investigation the effect of pH and reducing agent concentration on the structural properties of zinc-substitution magnetite nanoparticles,"Today, spinel ferrite nanoparticles are widely used in the medical field for
cancer treatment, drug delivery, and magnetic resonance imaging contrast agent
due to their superior magnetic properties and biocompatibility. Due to the
strong dependence of magnetic properties on morphology and other structural
aspects, the magnetic properties of these nanoparticles depend on their
manufacturing process. One of the goals of the researchers is to improve the
magnetic properties of these nanoparticles by substituting elements such as
manganese, cobalt, zinc, nickel, magnesium and iron. In this research, first,
magnetic Zn0.3Fe0.6O4 nanoparticles were synthesized by hydrothermal method in
the presence of citric acid as a reducing agent. In order to reduce the amount
of impurity and obtain the pure spinel phase and reduce the size of magnetic
nanoparticles, the hydrothermal process was carried out in the presence of
different concentrations of the reducing agent and pH level of the medium. The
structural investigations of the resulting nanoparticles were carried out by
X-ray diffraction (XRD) and scanning electron microscopy (SEM). The results
showed that in order to obtain pure and single-phase spinel nanoparticles with
appropriate particle size and size distribution, it is necessary to control the
concentration of reducing agent and pH.",2302.10168v1
2023-05-22,Experimental test of the Rosenzweig-Porter model for the transition from Poisson to Gaussian unitary ensemble statistics,"We report on an experimental investigation of the transition of a quantum
system with integrable classical dynamics to one with violated time-reversal
(T) invariance and chaotic classical counterpart. High-precision experiments
are performed with a flat superconducting microwave resonator with circular
shape in which T-invariance violation and chaoticity are induced by magnetizing
a ferrite disk placed at its center, which above the cutoff frequency of the
first transverse-electric mode acts as a random potential. We determine a
complete sequence of approx. 1000 eigenfrequencies and find good agreement with
analytical predictions for the spectral properties of the Rosenzweig-Porter
(RP) model, which interpolates between Poisson statistics expected for typical
integrable systems and Gaussian unitary ensemble statistics predicted for
chaotic systems with violated T invariance. Furthermore, we combine the RP
model and the Heidelberg approach for quantum-chaotic scattering to construct a
random-matrix model for the scattering (S) matrix of the corresponding open
quantum system and show that it perfectly reproduces the fluctuation properties
of the measured S matrix of the microwave resonator.",2305.12840v3
2023-05-24,Enhancement of synthetic magnetic field induced nonreciprocity via bound states in continuum in dissipatively coupled systems,"The nonreciprocal propagation of light typically requires use of materials
like ferrites or magneto-optical media with a strong magnetic bias or methods
based on material nonlinearities which require use of strong electromagnetic
fields. A simpler possibility to produce nonreciprocity is to use
spatio-temporal modulations to produce magnetic fields in synthetic dimensions.
In this paper we show that dissipatively coupled systems can lead to
considerable enhancement of nonreciprocity in synthetic fields. The enhancement
comes about from the existence of nearly nondecaying mode -bound state in
continuum (BIC) in dissipatively coupled systems. The dissipative coupling
occurs in a wide class of systems coupled via transmission lines, waveguides,
or nano fibers. The systems could be optical resonators or microscopic qubits.
Remarkably we find that for specific choice of the modulation amplitudes, the
transmission say in forward direction is completely extinguished whereas in the
backward direction it becomes maximum. The synthetic fields produce
transmission resonances which show significant line narrowing which owe their
origin to existence of BIC's in dissipative systems.",2305.14945v1
2023-06-19,Extreme nonreciprocity in metasurfaces based on bound states in the continuum,"Nonreciprocal devices, including optical isolators, phase shifters, and
amplifiers, are pivotal for advanced optical systems. However, exploiting
natural materials is challenging due to their weak magneto-optical effects,
requiring substantial thickness to construct effective optical devices. In this
study, we demonstrate that subwavelength metasurfaces supporting bound states
in the continuum and made of conventional magnetic ferrite can exhibit extreme
nonreciprocity in the Faraday configuration and near-unity magnetic circular
dichroism. These metasurfaces enhance the magneto-optical effect by 3--4 orders
of magnitude compared to a continuous film of the same material. This
significant enhancement is achieved by leveraging Huygens' condition in the
metasurface whose structural units support paired electric and magnetic dipole
resonances. We develop the multi-mode temporal coupled-mode theory for the
observed enhancement of the magneto-optical effect and confirm our findings
with the full-wave simulations.",2306.10827v1
2023-06-26,Dispersion of Multiferroic Nanoparticles in a Bent-Core Nematic Liquid Crystal: Experimental and Theoretical Study,"A novel nanocomposite system has been prepared by dispersing multiferroic
bismuth ferrite nanoparticles (BiFeO$_3$) in a bent-core nematic liquid crystal
(8-F-OH) that exhibits cybotactic clusters. Transition temperature, optical
textures, order parameter $S_m$, and dielectric spectroscopy experiments are
performed in the doped system, and the results are compared with the pure one.
The main experimental outcome is that the doped system has increased
orientational order parameters, even though the cybotactic cluster size is
reduced due to the incorporation of multiferroic BiFeO$_3$ nanoparticles. The
transition temperature, as observed under polarising optical microscopy,
clearly indicates a reduction of $1 - 2~ ^\circ{\rm C}$ in the doped system
compared to the pure one, and we conjecture this is due to the disordering of
the cybotactic cluster in the doped system. Based on the experimental findings,
a Landau-de Gennes-type free energy model is developed. The model qualitatively
explains the increased mean order parameter and the disordering of cybotactic
clusters with increasing polarization value of nanoparticles. This is
corroborated by experimental findings.",2306.14623v2
2023-06-29,Analytical approximations for magnetic coupling coefficients between adjacent coils,"This paper presents a simple yet novel two-dimensional modelling approach for
approximating the coupling coefficient between neighbouring inductors as a
function of co-planar separation and relative angular displacement. The
approach employs simple geometric arguments to predict the effective magnetic
flux between inductors. Two extreme coil geometry regimes are considered;
planar coils (i.e. on printed circuit board), and solenoid coils, each with
asymmetric ferrite cores about the central magnetic plane of the inductor. The
proposed geometric approximation is used to predict the coupling coefficient
between sensors as a function of separation distance and angular displacement
and the results are validated against two-dimensional finite element modelling
results. The analytical approximations show excellent agreement with the FE
analysis, predicting comparable trends with changing separation and angular
displacement, enabling best fitting to 2D FE and 3D numerical data with a
residual standard deviation of less than 0.5\% for the planar coil
approximation. The work demonstrates the validity of the analytical
approximation for predicting coupling behaviour between neighbouring coils.
This has practical uses for the automated estimation of the physical separation
between coils, or the curvature of surfaces they are rested or adhered to.",2306.16745v2
2023-07-03,Magnetic lump motion in saturated ferromagnetic films,"In this paper, we study in detail the nonlinear propagation of magnetic
soliton in a ferromagnetic film. The sample is magnetized to saturation by an
external field perpendicular to film plane. A new generalized (2+1)-dimensional
short-wave asymptotic model is derived. The bilinear-like forms of this
equation are constructed, and exact magnetic line soliton solutions are
exhibited. It is observed that a series of stable lumps can be generated by an
unstable magnetic soliton under Gaussian disturbance. Such magnetic lumps are
highly stable and can maintain their shapes and velocities during evolution or
collision. The interaction between lump and magnetic soliton, as well as
interaction between two lumps, are numerically investigated. We further discuss
the nonlinear motion of lumps in ferrites with Gilbert-damping and
inhomogeneous exchange effects. The results show that the Gilbert-damping
effects make the amplitude and velocity of the magnetic lump decay
exponentially during propagation. And the shock waves are generated from a lump
when quenching the strength of inhomogeneous exchange.",2307.00903v1
2023-07-18,Room-temperature magnetism and controlled cation distribution in vanadium ferrite thin films,"Spinel oxides demonstrate significant technological promise due to the vast
array of interrelated physical properties that their unique structure supports.
Specifically, the Fe1+xV2-xO4 spinel system garners extensive interest due to
the presence of orbitally ordered states and multiferroism. This study focuses
on the elaboration of high-quality Fe2VO4 (x = 1) thin films on MgO substrates
via pulsed laser deposition. Structural analyses confirm the epitaxial growth
of the films, their high crystallinity and fully strained nature. The cationic
distribution and stoichiometry were investigated using Resonant Elastic X-ray
Scattering experiments, in conjunction with comprehensive characterization of
the films' physical and electrical properties. The films exhibit
room-temperature magnetism, with a magnetization consistent with the
(Fe3+)Td[Fe2+V3+2]OhO4 inverse spinel structure unveiled by anomalous
diffraction. This work represents the inaugural successful deposition of Fe2VO4
thin films, thereby expanding the family of spinel vanadium oxide thin films
with a new member that demonstrates room-temperature magnetic properties.",2307.09598v1
2023-09-20,Construction of the Initial Part of a Ion Linear Accelerator from Similar Short Cavities,"The construction of the initial part of a normally conducting linac for
hydrogen ion beams with a pulsed current of ~20 mA up to an energy of ~70 MeV
is considered. The RFQ at a frequency of ~160 MHz accelerates ions to an energy
of ~4 MeV. Further acceleration is carried out at a doubled frequency by short,
up to $5\beta\lambda$, cavities, operating in the TM010 mode, with drift tubes.
Focusing is carried out by doublets of quadrupole lenses placed between the
cavities. The structure of the accelerating-focusing channel, with given beam
parameters, with reserves provides both the conditions for stable longitudinal
and transverse motion of particles, and reliable technical implementation. The
main results of the simulations of particle dynamics and the main parameters of
the elements of the channel are presented. The possibility of constructing an
linac with a higher output energy is analyzed.",2309.11431v1
2023-09-24,Effect of organic solvent on the cold sintering processing of SrFe12O19 platelet-based permanent magnets,"In this work we have investigated the effect of the solvent during the
processing of SrFe12O19 platelet-based permanent magnets by cold sintering
process (CSP) plus a post-thermal treatment. Several organic solvents: glacial
acetic acid, oleic acid and oleylamine have been analyzed, optimizing the CSP
temperatures at 190-270 {\deg}C, under pressures of 375-670 MPa and 6-50 wt% of
solvent. Modifications in the morphological and structural properties are
identified depending on the solvent, which impacts on the magnetic response.
Independently of the solvent, the mechanical integrity of ferrite magnets
obtained by CSP is improved by a post-annealing at 1100 {\deg}C for 2 h,
resulting in relative densities around 92 % with an average grain size of 1
{\mu}m and a fraction of SrFe12O19 phase > 91 %. Hc > 2.1 kOe and MS of 73
emu/g are obtained in the final sintered ceramic magnets, exhibiting the
highest HC value of 2.8 kOe for the magnet sintered using glacial acetic acid.",2309.15859v1
2023-10-06,Fast Output Energy Regulation in a Medical Proton Linac,"In proton therapy, depth scanning of the irradiated object is performed by
changing the Output Energy (OE) of the accelerated beam. In pulsed linear
accelerators, adjustment of the OE is usually by changing the amplitude and/or
phase of the field in the accelerating elements from one RF pulse to another.
The application of non-inertial traveling wave accelerating sections makes it
possible to change quickly the phase of the accelerating field during the RF
pulse. The phase of the field in the constant gradient section is determined
both by the phase of the input RF signal and by the process of wave propagation
in the dispersive structure. The calculation results of the traveling wave
propagation in the accelerating structure when the phase of the input RF signal
changes and the results of simulation the dynamics of particles confirm the
change in the linac's OE during the RF pulse. The proposed method for
regulation the OE makes it possible to increase in orders the speed of scanning
the irradiated object by depth.",2310.04262v1
2023-10-23,Design of the LLRF control system for MA cavity at CSNS RCS,"The China Spallation Neutron Source (CSNS) beam power was successfully
reached 125 kW with a low beam loss in February 2022. In order to increase beam
power, during the summer in 2022, we employ magnetic-alloy (MA) cavity in the
rapid cycling synchrotron (RCS). It is a wideband cavity (Q=2), allows the
second harmonic rf (h= 4) operation, with the existing ferrite cavity to
realize the dual-harmonic acceleration. The second harmonic (h=4) is used for
the bunch shape control and alleviating the space charge effects. We design of
the low-level RF(LLRF) control system for MA cavity, in this paper, we describe
the system design and implementation, and the preliminary test results.",2310.14915v1
2023-11-16,Persistent anisotropy of the spin cycloid in BiFeO3 through ferroelectric switching,"A key challenge in antiferromagnetic spintronics is the control of spin
configuration on nanometer scales applicable to solid-state technologies.
Bismuth ferrite (BiFeO3) is a multiferroic material that exhibits both
ferroelectricity and canted antiferromagnetism at room temperature, making it a
unique candidate in the development of electric-field controllable magnetic
devices. The magnetic moments in BiFeO3 are arranged into a spin cycloid,
resulting in unique magnetic properties which are tied to the ferroelectric
order. Previous understanding of this coupling has relied on average, mesoscale
measurements to infer behavior. Using nitrogen vacancy-based diamond
magnetometry, we show that the spin cycloid can be deterministically controlled
with an electric field. The energy landscape of the cycloid is shaped by both
the ferroelectric degree of freedom and strain-induced anisotropy, restricting
the magnetization changes to specific ferroelectric switching events. This
study provides understanding of the antiferromagnetic texture in BiFeO3 and
paves new avenues for designing magnetic textures and spintronic devices.",2311.10169v1
2023-12-14,Confinement of electron holes via the peroxo group formation in the negative charge-transfer materials on the example of SrFeO3: plane-wave density functional theory predictions,"The present work puts forward a concept that the thermostable O1s XPS peaks
with energy of about 531 eV in negative charge-transfer SrFeO_{3-\delta}
perovskite are determined by the peroxo-like oxygen species. The peroxo group
forms via coupling two oxygen anions coordinated to iron cations with
d^5\bar-under{L} (\bar-under{L}-oxygen electron hole) configuration. By means
of plane-wave DFT+U approach there have been shown that the peroxo group
represents a metastable state in the absence of oxygen vacancies nearby. The
O-O bonding confines two electron holes freezing the 3+ oxidation state for two
iron cations bridged by peroxide. Increasing the peroxo group numbers makes the
ferrite a semiconductor with charge-transfer gap of about 0.6 eV.",2312.08665v1
2024-01-11,A first-principles study of Zn induced liquid metal embrittlement at bcc and fcc grain boundaries,"Zn induced liquid metal embrittlement (LME) is a major concern in particular
for advanced high strength steels, which often contain a significant amount of
austenite compared to established steel grades. Using density functional theory
(DFT) calculations we, therefore, compare the behaviour of Zn in ferrite (bcc)
and austenite (fcc) grain boundaries (GBs) with different magnetic ordering to
investigate the role of crystal structure as well as magnetism in LME. We
address the performance of DFT based paramagnetic calculations by utilizing the
spin space averaging relaxation approach. Our results show that both magnetic
and elastic contributions have significant influence towards segregation and
embrittling behaviour of Zn. The primary requirement is the elastic
contribution, while the presence of magnetic disorder increases the critical
concentrations for the onset of GB weakening. While Zn segregation is more
favourable in bcc compared to fcc GB, larger impact of Zn coverage on GB
weakening is observed for fcc. For both structures, the rapid decrease in
surface defect state energies is identified as the driving force behind GB
weakening. These surface defect states stabilize at lower Zn concentrations
than GB defect states.",2401.05997v1
2024-02-22,Barium hexaferrite-based nanocomposites as Random Magnets for microwave absorption H,"The present work reports experimental evidence of random magnetic behavior
observed in modified barium hexagonal ferrites. A significant transition in the
magnetic properties of this system is observed when divalent cations (Ni2+,
Cu2+, Mn2+) are introduced in the structure and give rise to a magnetic
nanocomposite. Such introduction takes place in a random manner throughout each
sample and creates the conditions for such materials to behave as random
magnets. We verify the occurrence of such behavior in our samples by fitting
the magnetization in approaching saturation to the corresponding theoretical
model. We therefore analyze the microwave absorption capacities of random
magnets in the GHz range and predict large and broad absorption signals under
certain conditions. The findings presented here postulate, for the first time,
ceramic materials as promising random magnets and underline their potential as
microwave absorbers, in good agreement with recent theoretical models.",2402.14324v1
2006-11-20,Cationic exchange in nanosized ZnFe2O4 spinel revealed by experimental and simulated near-edge absorption structure,"The non-equilibrium cation site occupancy in nanosized zinc ferrites (6-13
nm) with different degree of inversion (0.2 to 0.4) was investigated using Fe
and Zn K-edge x-ray absorption spectroscopy XANES and EXAFS, and magnetic
measurements. The very good agreement between experimental and ab-initio
calculations on the Zn K-edge XANES region clearly show the large
Zn2+(A)--Zn2+[B] transference that takes place in addition to the
well-identified Fe3+[B]--Fe3+(A) one, without altering the long-range
structural order. XANES spectra features as a function of the spinel inversion
were shown to depend on the configuration of the ligand shells surrounding the
absorbing atom. This XANES approach provides a direct way to sense cationic
inversion in these spinel compounds. We also demonstrated that a mechanical
crystallization takes place on nanocrystalline spinel that causes an increase
of both grain and magnetic sizes and, simultaneously, generates a significant
augment of the inversion.",0611532v2
2005-02-03,Spacetime Deformations and Electromagnetism in Material Media,"This paper is intended to investigate the relation between electrodynamics in
anisotropic material media and its analogous formulation in an spacetime, with
non-null Riemann curvature tensor. After discussing the electromagnetism via
chiral differential forms, we point out the optical activity of a given
material medium, closely related to topological spin, and the Faraday rotation,
associated to topological torsion. Both quantities are defined in terms of the
magnetic potential and the electric and magnetic fields and excitations. We
revisit some properties of material media and the associated Green dyadics.
Some related features of ferrite are also investigated. It is well-known that
the constitutive tensor is essentially equivalent to the Riemann curvature
tensor. In order to investigate the propagation of electromagnetic waves in
material media, we prove that it is analogous to consider the electromagnetic
wave propagation in the vacuum, but this time in a curved spacetime, which is
obtained by a deformation of the lorenztian metric of Minkowski spacetime.
Spacetime deformations leave invariant the form of Maxwell equations. Also,
there exists a close relation between Maxwell equations in curved spacetime and
in an anisotropic material medium, indicating that electromagnetism and
spacetime properties are deeply related. Besides, the geometrical aspects of
wave propagation can be described by an effective geometry which represents a
deformation of the lorentzian metric of Minkowski spacetime.",0502012v4
2005-03-01,Advanced bridge (interferometric) phase and amplitude noise measurements,"The measurement of the close-to-the-carrier noise of rf and microwave devices
is a relevant issue in time and frequency metrology and in some fields of
electronics, physics and optics. While phase noise is the main concern,
amplitude noise is often of interest. The highest sensitivity is achieved with
the bridge (interferometric) method, which consists of the amplification and
synchronous detection of the noise sidebands after suppressing the carrier by
vector subtraction of an equal signal. A substantial progress in understanding
the flicker noise mechanism of the interferometer results in new schemes that
improve by 20--30 dB the sensitivity at low Fourier frequencies.
  The article provides the complete theory and detailed design criteria, and
reports on the implementation of a prototype. In real-time measurements, a
background noise of -175 -180 dBrad^2/Hz has been obtained at f=1 Hz off the
100 MHz carrier. Exploiting correlation and averaging in similar conditions,
the sensitivity exceeds -185 dBrad^2/Hz at f=1 Hz. A residual noise of -203
dBrad^2/Hz at f=250 Hz off the carrier has been obtained, while the ultimate
noise floor is still limited by the averaging capability of the correlator.
This is equivalent to a S/N ratio of 2E20 with a frequency spacing of 2.5E-6.
  Applications include the measurement of the properties of materials and the
observation of weak flicker-type physical phenomena, out of reach for other
instruments. We measured the flicker noise of a by-step attenuator (-171
dB[rad^2]/Hz at f=1 Hz) and of the ferrite noise of a reactive power divider
(-173.7 dB[rad^2]/Hz at f=1 Hz) without need of correlation.",0503015v1
2006-01-24,Trapping atoms on a transparent permanent-magnet atom chip,"We describe experiments on trapping of atoms in microscopic magneto-optical
traps on an optically transparent permanent-magnet atom chip. The chip is made
of magnetically hard ferrite-garnet material deposited on a dielectric
substrate. The confining magnetic fields are produced by miniature magnetized
patterns recorded in the film by magneto-optical techniques. We trap Rb atoms
on these structures by applying three crossed pairs of counter-propagating
laser beams in the conventional magneto-optical trapping (MOT) geometry. We
demonstrate the flexibility of the concept in creation and in-situ modification
of the trapping geometries through several experiments.",0601163v2
2007-06-19,Synthesis and magnetic properties of NiFe_{2-x}Al_{x}O_{4} nanoparticles,"Nanocrystalline Al-doped nickel ferrite powders have been synthesized by
sol-gel auto-ignition method and the effect of non-magnetic aluminum content on
the structural and magnetic properties has been studied. The X-ray diffraction
(XRD) revealed that the powders obtained are single phase with inverse spinel
structure. The calculated grain sizes from XRD data have been verified using
transmission electron microscopy (TEM). TEM photographs show that the powders
consist of nanometer-sized grains. It was observed that the characteristic
grain size decreases from 29 to 6 nm as the non-magnetic Al content increases,
which was attributed to the influence of non-magnetic Al concentration on the
grain size. Magnetic hysteresis loops were measured at room temperature with a
maximum applied magnetic field of 1T. As aluminum content increases, the
measured magnetic hysteresis curves become more and more narrow and the
saturation magnetization and remanent magnetization both decreased. The
reduction of agnetization compared to bulk is a consequence of spin
non-collinearity. Further reduction of magnetization with increase of aluminum
content is caused by non-magnetic Al^{3+} ions and weakened interaction between
sublattices. This, as well as the decrease in hysteresis was understood in
terms of the decrease in particle size.",0706.2794v1
2008-06-12,"Comment on ""Ferroelectrically Induced Weak Ferromagnetism by Design"", C. Fennie, PRL 100, 167203 (2008)","The question of how ferroelectric polarization is coupled to magnetism in
magnetoelectric multiferroics, in which both types of order are simultaneously
present, is of considerable scientific and practical interest. A recent Letter
\cite{fennie} presents an analysis of the important ``ABO$_3$'' class of
perovskite multiferroics. This Letter argues that antiferromagnetic
multiferroics with magnetic ions on the B site, such as the well-studied
room-temperature multiferroic bismuth ferrite (A=Bi, B=Fe), cannot show linear
magnetoelectric coupling of the form ${\bf P} \cdot ({\bf L} \times {\bf M})$.
Here ${\bf P}$ is polarization and ${\bf L}$ and ${\bf M}$ are
antiferromagnetic and ferromagnetic moments. The conclusion of Ref.
\onlinecite{fennie} is that only materials with magnetic A-site have this
coupling. This Comment presents a compact analysis of magnetoelectric coupling
in the ABO$_3$ multiferroics. We show that the argument of Ref.
\onlinecite{fennie} does forbid $E_{PLM}$ if the final low-symmetry phase
contains only one distortion that, like ${\bf P}$, breaks all inversion
symmetries. In reality, there are multiple distortions in this symmetry class,
and cross-terms generate $E_{PLM}$. Our analysis gives simple conclusions about
existence and optimization of magnetoelectric coupling in ABO$_3$ materials.",0806.2142v4
2009-07-21,Ferromagnetic transition metal implanted ZnO: a diluted magnetic semiconductor?,"Recently theoretical works predict that some semiconductors (e.g. ZnO) doped
with magnetic ions are diluted magnetic semiconductors (DMS). In DMS magnetic
ions substitute cation sites of the host semiconductor and are coupled by free
carriers resulting in ferromagnetism. One of the main obstacles in creating DMS
materials is the formation of secondary phases because of the solid-solubility
limit of magnetic ions in semiconductor host. In our study transition metal
ions were implanted into ZnO single crystals with the peak concentrations of
0.5-10 at.%. We established a correlation between structural and magnetic
properties. By synchrotron radiation X-ray diffraction (XRD) secondary phases
(Fe, Ni, Co and ferrite nanocrystals) were observed and have been identified as
the source for ferromagnetism. Due to their different crystallographic
orientation with respect to the host crystal these nanocrystals in some cases
are very difficult to be detected by a simple Bragg-Brentano scan. This results
in the pitfall of using XRD to exclude secondary phase formation in DMS
materials. For comparison, the solubility of Co diluted in ZnO films ranges
between 10 and 40 at.% using different growth conditions pulsed laser
deposition. Such diluted, Co-doped ZnO films show paramagnetic behaviour.
However, only the magnetoresistance of Co-doped ZnO films reveals possible s-d
exchange interaction as compared to Co-implanted ZnO single crystals.",0907.3536v1
2010-01-12,Phonon Spectroscopy Near Phase Transition Temperatures in Multferroic BiFeO3 Epitaxial Thin Films,"We report a Raman scattering investigation of multiferroic bismuth ferrite
BiFeO3 epitaxial (c-axis oriented) thin films from -192 to 1000C. Phonon
anomalies have been observed in three temperature regions: in the gamma-phase
from 930C to 950C; at ~370C, Neel temperature (TN), and at ~123C, due to a
phase transition of unknown type (magnetic or structural). An attempt has been
made to understand the origin of the weak phonon-magnon coupling and the
dynamics of the phase sequence. The disappearance of several Raman modes at
~820C (Tc) is compatible with the known structural phase transition and the
Pbnm orthoferrite space group assigned by Arnold {\it et al.} \cite{arnold:09}.
The spectra also revealed a {\it non-cubic} $\beta$-phase from 820-930\dc and
the same {\it non-cubic} phase extends through the $\gamma$-phase between
930-950\dc, in agreement with Arnold {\it et al.} \cite{arnold2:09}, and an
evidence of a cubic $\delta$-phase around 1000\dc in thin films that is not
stable in powder and bulk. Such a cubic phase has been theoretically predicted
in \cite{vasquez:prb09}. Micro-Raman scattering and X-ray diffraction showed no
structural decomposition in thin films during the thermal cycling from
22-1000\dc.",1001.1997v1
2010-12-16,Coupled states of electromagnetic fields with magnetic-dipolar-mode vortices: MDM-vortex polaritons,"Under the influence of the material environment, electromagnetic fields in
the near-field regime exhibit quite different nature from those in the
far-field free space. A coupled state of an electromagnetic field with an
electric or magnetic dipole-carrying excitation is well known as a polariton.
Such a state is the result of the mixing of a photon with an excitation of a
material. The most discussed types of polaritons are phonon-polaritons,
exciton-polaritons, and surface plasmon-polaritons. Recently, it was shown that
in microwaves strong magnon-photon coupling can be achieved due to
magnetic-dipolar-mode (MDM) vortices in small thin-film ferrite disks. These
coupled states can be specified as MDM-vortex polaritons. In this paper we
study properties of MDM-vortex polaritons. We show that MDM-vortex polaritons
are characterized by helicity behaviors. For the observed frequency splits of
MDM resonances there are different-type helicities. In the split-resonance
states one has or localization, or cloaking of electromagnetic fields. We
analyze numerically a variety of the field topological structures of MDM-vortex
polaritons and give theoretical insights into the possible origin of such
topologically distinctive states. The shown properties of MDM-vortex polaritons
can be useful for realization of novel microwave metamaterial structures and
near-field sensing applications.",1012.3621v1
2011-03-05,Physics and measurements of magnetic materials,"Magnetic materials, both hard and soft, are used extensively in several
components of particle accelerators. Magnetically soft iron-nickel alloys are
used as shields for the vacuum chambers of accelerator injection and extraction
septa; Fe-based material is widely employed for cores of accelerator and
experiment magnets; soft spinel ferrites are used in collimators to damp
trapped modes; innovative materials such as amorphous or nanocrystalline core
materials are envisaged in transformers for high-frequency polyphase resonant
convertors for application to the International Linear Collider (ILC). In the
field of fusion, for induction cores of the linac of heavy-ion inertial fusion
energy accelerators, based on induction accelerators requiring some 107 kg of
magnetic materials, nanocrystalline materials would show the best performance
in terms of core losses for magnetization rates as high as 105 T/s to 107 T/s.
After a review of the magnetic properties of materials and the different types
of magnetic behaviour, this paper deals with metallurgical aspects of
magnetism. The influence of the metallurgy and metalworking processes of
materials on their microstructure and magnetic properties is studied for
different categories of soft magnetic materials relevant for accelerator
technology. Their metallurgy is extensively treated. Innovative materials such
as iron powder core materials, amorphous and nanocrystalline materials are also
studied. A section considers the measurement, both destructive and
non-destructive, of magnetic properties. Finally, a section discusses magnetic
lag effects.",1103.1069v1
2012-08-27,Piezoelectric nonlinearity and frequency dispersion of the direct piezoelectric response of BiFeO3 ceramics,"We report on the frequency and stress dependence of the direct piezoelectric
d33 coefficient in BiFeO3 ceramics. The measurements reveal considerable
piezoelectric nonlinearity, i.e., dependence of d33 on the amplitude of the
dynamic stress. The nonlinear response suggests a large irreversible
contribution of non-180{\deg} domain walls to the piezoelectric response of the
ferrite, which, at present measurement conditions, reached a maximum of 38% of
the total measured d33. In agreement with this interpretation, both types of
non-180{\deg} domain walls, characteristic for the rhombohedral BiFeO3, i.e.,
71{\deg} and 109{\deg}, were identified in the poled ceramics using
transmission electron microscopy (TEM). In support to the link between
nonlinearity and non-180{\deg} domain wall contribution, we found a correlation
between nonlinearity and processes leading to deppining of domain walls from
defects, such as quenching from above the Curie temperature and
high-temperature sintering. In addition, the nonlinear piezoelectric response
of BiFeO3 showed a frequency dependence that is qualitatively different from
that measured in other nonlinear ferroelectric ceramics, such as ""soft""
(donor-doped) Pb(Zr,Ti)O3 (PZT); possible origins of this dispersion are
discussed. Finally, we show that, once released from pinning centers, the
domain walls can contribute extensively to the electromechanical response of
BiFeO3; in fact, the extrinsic domain-wall contribution is relatively as large
as in Pb-based ferroelectric ceramics with morphotropic phase boundary (MPB)
composition, such as PZT. This finding might be important in the search of new
lead-free MPB compositions based on BiFeO3 as it suggests that such
compositions might also exhibit large extrinsic domain-wall contribution to the
piezoelectric response.",1208.5426v1
2012-12-06,Theoretical and numerical study of lamellar eutectoid growth influenced by volume diffusion,"We investigate the lamellar growth of pearlite at the expense of austenite
during the eutectoid transformation in steel. To begin with, we extend the
Jackson-Hunt-type calculation (previously used to analyze eutectic
transformation) to eutectoid transformation by accounting for diffusion in all
the phases. Our principal finding is that the growth rates in presence of
diffusion in all the phases is different as compared to the case when diffusion
in growing phases is absent. The difference in the dynamics is described by a
factor '{\rho}' which comprises of the ratio of the diffusivities of the bulk
and the growing phases, along with the ratios of the slopes of the phase
co-existence lines. Thereafter, we perform phase-field simulations, the results
of which are in agreement with analytical predictions. The phase-field
simulations also reveal that diffusion in austenite as well as ferrite leads to
the formation of tapered cementite along with an overall increase in the
transformation kinetics as compared to diffusion in austenite (only). Finally,
it is worth noting that the aim of present work is not to consider the
pearlitic transformation in totality, rather it is to isolate and thereby
investigate the influence of diffusivity in the growing phases on the front
velocity.",1212.1250v4
2012-12-12,Ferrimagnetism and spin canting of ZnFe2O4 nanoparticles embedded in ZnO matrix,"The structural and magnetic properties of ZnFe2O4 nanoparticles embedded in a
non-magnetic ZnO matrix are presented. X-ray diffractograms and Transmission
Electron Microscopy (TEM) images showed that the resulting samples are composed
of crystalline ferrite nanoparticles with average crystallite size <D> =
23.4(0.9) nm, uniformly dispersed within the ZnO matrix. Magnetization data
indicated a superparamagnetic-like behavior from room temperature down to T_{M}
~ 20 K, where a transition to a frozen state is observed. The M(H) curves
displayed nearly zero coercive field down to TM, where a sharp increase in the
H_C value is observed. The measured saturation magnetization M_S values at 200
and 2 K were M_S = 0.028(3) and 0.134(7) muB/f.u. ZnFe2O4 respectively, showing
the existence of small amounts of non compensated atomic moments. M\""ossbauer
measurements at low temperatures confirmed the transition to a magnetically
ordered state for T < 25 K, where two magnetically split sextets develop.
Whereas these two sextets show strong overlap due to the similar hyperfine
fields, in-field M\""ossbauer spectra clearly showed two different Fe3+ sites,
demonstrating that the sample is ferrimagnetically ordered. The two spinel
sites are found to behave differently under an external field of 12 T: whereas
the moments located at A sites show a perfect alignment with the external
field, spins at B sites are canted by an angle alpha_B = 49(2){\deg}. We
discuss the significance of this particle structure for the observed magnetic
behavior.",1212.2798v1
2013-03-12,Démixtion et ségrégation superficielle dans les alliages fer-chrome,"Ferritic steels possibly strengthened by oxide dispersion are candidates as
structural materials for generation IV and fusion nuclear reactors. Their use
is limited by incomplete knowledge of the iron-chromium phase diagram at low
temperatures and of the phenomena inducing preferential segregation of one
element at grain boundaries or at surfaces. In this context, this work
contributes to the multi-scale study of the model iron-chromium alloy and their
free surfaces by numerical simulations. This study begins with ab initio
calculations of properties related to the mixture of atoms of iron and
chromium. We highlight complex dependency of the magnetic moments of the
chromium atoms on their local chemical environment. Surface properties are also
proving sensitive to magnetism. This is the case of impurity segregation of
chromium in iron and of their interactions near the surface. In a second step,
we construct a simple energy model for high numerical efficiency. It is based
on pair interactions on a rigid lattice to which are given local chemical
environment and temperature dependencies. With this model, we reproduce the ab
initio results at zero temperature and experimental results at high
temperature. We also deduce the solubility limits at all intermediate
temperatures with mean field approximations that we compare to Monte Carlo
simulations. The last step of our work is to introduce free surfaces in our
model. We then study the effect of ab initio calculated bulk and surface
properties on surface segregation. Finally, we calculate segregation isotherms.
We therefore propose an evolution model of surface composition of iron-chromium
alloys as a function of bulk composition.",1303.2938v1
2013-04-23,Quantitative study of the spin Hall magnetoresistance in ferromagnetic insulator/normal metal hybrids,"We experimentally investigate and quantitatively analyze the spin Hall
magnetoresistance effect in ferromagnetic insulator/platinum and ferromagnetic
insulator/nonferromagnetic metal/platinum hybrid structures. For the
ferromagnetic insulator we use either yttrium iron garnet, nickel ferrite or
magnetite and for the nonferromagnet copper or gold. The spin Hall
magnetoresistance effect is theoretically ascribed to the combined action of
spin Hall and inverse spin Hall effect in the platinum metal top layer. It
therefore should characteristically depend upon the orientation of the
magnetization in the adjacent ferromagnet, and prevail even if an additional,
nonferromagnetic metal layer is inserted between Pt and the ferromagnet. Our
experimental data corroborate these theoretical conjectures. Using the spin
Hall magnetoresistance theory to analyze our data, we extract the spin Hall
angle and the spin diffusion length in platinum. For a spin mixing conductance
of $4\times10^{14}\;\mathrm{\Omega^{-1}m^{-2}}$ we obtain a spin Hall angle of
$0.11\pm0.08$ and a spin diffusion length of $(1.5\pm0.5)\;\mathrm{nm}$ for Pt
in our thin film samples.",1304.6151v1
2013-06-11,Crossover from injection to tunneling conduction mode and associated magneto-resistance in a single $Fe_{3}O_{4}$(111)/$Alq_{3}$/Co spin-valve device,"We demonstrate interface energy level engineering, exploiting the
modification in energy band structure across Verwey phase transition of
$Fe_{3}O_{4}$ electrode, in a $Fe_{3}O_{4}$(111)/$Alq_{3}$/Co vertical
spin-valve (SV) device. Experimental results on device characteristics I-V)
study exhibit a transition in conduction mode from carrier injection to
tunneling across Verwey transition temperature ($T_{V}$) of $Fe_{3}O_{4}$
electrode. Both giant magneto-resistance (GMR) and tunneling MR (TMR) have been
observed in a single SV device as a function of temperature, below and above
$T_{V}$, respectively. Appearance of GMR, accompanied by injection limited
natural Schottky-like I-V characteristics, provide evidences of spin injection
at electrode/$Alq_{3}$ interface and transport through molecular orbitals in
this SV device. Features of TMR exhibit significant differences from that of
GMR. This is due to the dominant hyperfine-field interaction in the multi-step
tunneling regime. We have achieved room-temperature SV operation in our device.
A phenomenological model for device operation has been proposed to explain the
transition in the conduction mode and associated MR features across $T_{V}$. We
propose that the tuning of charge gap at Fermi level across Verwey transition
due to charge ordering on the octahedral iron sites of $Fe_{3}O_{4}$ results in
a corresponding tuning of conduction mode causing this unique cross over from
GMR to TMR in this ferrite-based organic SV.",1306.2490v1
2013-06-25,Nonmonotonic Relaxation as a Result of Spatial Heterogeneity in the Model of In-series Blocks Chain,"Recently the materials possessing structure of molecular and supramolecular
matrix are more and more actively studied. They are relative to many polymeric
materials of a technological origin, such as rubber, and living biological
tissues. Processes of mechanical deformation of these continuous media have
peculiarities connected, first, with accounting for internal friction and
dissipation of energy, and secondly, with nonlinearity of their elastic and
viscous properties, that is with violation of Hook and Newtons laws.
Traditional approaches to mechanics of viscoelastic bodies sometimes are
excessively difficult, and more evident and available representations are
necessary. The invaluable role in studying of the operating processes
mechanisms of elastic deformation and motility of biological materials is
played by the mathematical modeling. New effect obtained by means of computer
experiment of nonmonotonic relaxation of deformation in heterogeneous media is
considered in the present work. Rheological properties of described media are
governed by the differential equations of the first order on time (the
evolution equations), as well as a huge variety of other physical processes.
The physical phenomena in nonlinear systems with dissipation have a big
community, including such it would seem far areas, as dynamics of magnetization
in ferrite. Therefore the problem of studying new effects of viscous friction
in the conditions of nonlinearity and heterogeneity, is very actual as in
respect of fundamental research nonlinear and non-uniform environments, and in
many areas of materials science, design of new materials, engineering of
biological substitutes of living tissues and development of the micromagnetic
devices using essentially new opportunities.",1306.5845v2
2013-11-23,Universal Scaling Law to Predict the Efficiency of Magnetic Nanoparticles as MRI T2-Contrast Agents,"Magnetic particles are very efficient Magnetic Resonance Imaging (MRI)
contrast agents. In the recent years, chemists have unleashed their imagination
to design multi-functional nanoprobes for biomedical applications including MRI
contrast enhancement. This study is focused on the direct relationship between
the size and magnetization of the particles and their nuclear magnetic
resonance relaxation properties, which condition their efficiency. Experimental
relaxation results with maghemite particles exhibiting a wide range of sizes
and magnetizations are compared to previously published data and to
well-established relaxation theories with a good agreement. This allows
deriving the experimental master curve of the transverse relaxivity versus
particle size and to predict the MRI contrast efficiency of any type of
magnetic nanoparticles. This prediction only requires the knowledge of the size
of the particles impermeable to water protons and the saturation magnetization
of the corresponding volume. To predict the T2 relaxation efficiency of
magnetic single crystals, the crystal size and magnetization obtained through a
single Langevin fit of a magnetization curve is the only information needed.
For contrast agents made of several magnetic cores assembled into various
geometries (dilute fractal aggregates, dense spherical clusters, core-shell
micelles, hollow vesicles), one needs to know a third parameter, namely the
intra-aggregate volume fraction occupied by the magnetic materials relatively
to the whole (hydrodynamic) sphere. Finally a calculation of the maximum
achievable relaxation effect and the size needed to reach this maximum is
performed for different cases: maghemite single crystals and dense clusters,
core-shell particles (oxide layer around a metallic core) and zinc manganese
ferrite crystals.",1311.6022v1
2014-01-16,Effect of Structural Transition on Magnetic Properties of Ca and Mn co-substituted BiFeO3 Ceramics,"Composition-driven structural transitions in Bi1-xCaxFe1-xMnxO3 ceramics
prepared by the tartaric acid modified sol-gel technique have been studied to
analyze its effect on the magnetic properties of bismuth ferrite (BiFeO3). It
was observed that the co-substitution of Ca & Mn at Bi & Fe sites in BiFeO3
(BFO) significantly suppress the impurity phases. The quantitative
crystallographic phase analysis has been carried out by double phase Rietveld
analysis of all the XRD patterns which indicates the existence of compositional
driven crystal structure transformation from rhombohederal (R3c space group,
lower crystal symmetry) to the orthorhombic (Pbnm space group, higher crystal
symmetry) with the increase in substitution concentration due to excess
chemical pressure (lattice strain). Magnetic measurements reveal that
co-substituted BFO nanoparticles for x = 0.15 have enhanced remnant
magnetization about 14 times that of pure one due to the suppression of cycloid
spin structure which could be explained in terms of field induced spin
reorientation and weak ferromagnetism. However, at the morphological phase
boundary (x = 0.15), the remnant and maximum magnetization at 8 T reaches a
maximum which indicates almost broken spin cycloid structure and further
increase in substitution results in the reduction of both magnetizations due to
the appearance of complete antiferromagnetic ordering in the orthorhombic
structure because of the significant contribution from the crystallographic
phase of Pbnm space group (as obtained from double phase Rietveld analysis).",1401.4059v1
2014-04-11,Effect of Structural Transition on Magnetic and Dielectric Properties of La and Mn co-substituted BiFeO3 Ceramics,"Bi1-xLaxFe1-xMnxO3 (x = 0.000 - 0.300) ceramics prepared by the tartaric acid
modified sol-gel technique have been studied to analyze the effect of
composition driven structural transition on the magnetic properties of bismuth
ferrite (BiFeO3). It was found that the co-substitution of La & Mn at Bi & Fe
sites leads to suppression of impurity phases (Bi2Fe4O9 and Bi25FeO40) which
generally appear in BiFeO3. The quantitative crystallographic phase analysis
has been carried out by double phase Rietveld analysis of all the XRD patterns
which indicates the existence of compositional driven crystal structure
transformation from rhombohederal (space group R3c) to the orthorhombic (space
group Pbnm) with the increase in substitution concentration. The 5%
co-substituted sample exhibit high remnant magnetization i.e. about 15 times
that of BiFeO3 which is due to the suppression of cycloid spin structure and
enhanced canting angle of antiferromagnetically ordered spins caused by the
crystal lattice distortion. However, further increase in substitution results
in the reduction of remnant magnetization and coercivity due to the appearance
of complete antiferromagnetic ordering in the orthorhombic structure because of
the significant contribution from the crystallographic phase of Pbnm space
group (as obtained from double phase Rietveld analysis). The frequency
independent higher dielectric constant and lower dielectric loss were observed
for 5% co-substitution. Hence, this particular composition may be interesting
for device applications.",1404.3025v2
2014-04-14,Magneto-photonic phenomena at terahertz frequencies,"Magneto-terahertz phenomena are the main focus of the thesis. This work
started as supporting research for the science of an X-ray laser (SwissFEL).
X-ray lasers have recently drawn great attention as an unprecedented tool for
scientific research on the ultrafast scale..... To answer this fundamental
question, we performed original numerical simulations using a coupled Landau-
Lifshitz-Gilbert Maxwell model. ... Those requirements were the motivations for
the experiments performed in the second part of the thesis. To shape the
terahertz pulses, .... Regarding the field intensities, we followed two
approaches. The first deals with field enhancement in nanoslits arrays. We
designed a subwavelength structure characterized by simultaneous high field
enhancement and high transmission at terahertz frequencies to suit nonlinear
sources. The second approach depended on up-scaling the generation from
laser-induced plasma by increasing the pump wavelengths. Numerical calculations
have also brought to our attention the importance of linear magnetoterahertz
effects. In particular, the simulations showed that the ultrafast dynamics
could lead to significant rotation of the polarization plane of the triggering
terahertz pulse. Motivated by this finding, we focused in the last part of the
thesis on the linear effects. We performed three original studies coming out
with first demonstrations of broadband non-reciprocal terahertz phase
retarders, terahertz magnetic modulators, and the non-reciprocal terahertz
isolators. In the first two experiments, we extended the unique properties of
the magnetic liquids (Ferrofluids) to the terahertz regime. In the latter
experiment, we used a permanent magnet (Ferrite) to experimentally show
complete isolation (unidirectional transmission) of the terahertz waves.",1404.3764v1
2014-07-11,Effects of dilute substitutional solutes on carbon in $α$-Fe: interactions and associated carbon diffusion from first-principles calculations,"By means of first-principles calculations coupled with the kinetic Monte
Carlo simulations, we have systematically investigated the effects of dilute
substitutional solutes on the behaviors of carbon in $\alpha$-Fe. Our results
uncover that: ($i$) Without the Fe vacancy the interactions between most
solutes and carbon are repulsive due to the strain relief, whereas Mn has a
weak attractive interaction with its nearest-neighbor carbon due to the local
ferromagnetic coupling effect. ($ii$) The presence of the Fe vacancy results in
attractive interactions of all the solutes with carbon. In particular, the
Mn-vacancy pair shows an exceptionally large binding energy of -0.81 eV with
carbon. ($iii$) The alloying addition significantly impacts the atomic-scale
concentration distributions and chemical potential of carbon in the Fe matrix.
Among them, Mn and Cr increase the carbon chemical potential whereas Al and Si
reduce it. ($iv$) Within the dilute scale of the alloying solution, the solute
concentration and temperature dependent carbon diffusivities demonstrate that
Mn has a little impact on the carbon diffusion whereas Cr (Al or Si) remarkably
retards the carbon diffusion. Our results provide certain implication for
better understanding the experimental observations related with the carbon
solubility limit, carbon micro-segregation and carbide precipitations in the
ferritic steels.",1407.2993v1
2014-07-27,Josephson parametric phase-locked oscillator and its application to dispersive readout of superconducting qubits,"The parametric phase-locked oscillator (PPLO), also known as a parametron, is
a resonant circuit in which one of the reactances is periodically modulated. It
can detect, amplify, and store binary digital signals in the form of two
distinct phases of self-oscillation. Indeed, digital computers using PPLOs
based on a magnetic ferrite ring or a varactor diode as its fundamental logic
element were successfully operated in 1950s and 1960s. More recently, basic bit
operations have been demonstrated in an electromechanical resonator, and an
Ising machine based on optical PPLOs has been proposed. Here, using a PPLO
realized with Josephson-junction circuitry, we demonstrate the demodulation of
a microwave signal digitally modulated by binary phase-shift keying. Moreover,
we apply this demodulation capability to the dispersive readout of a
superconducting qubit. This readout scheme enables a fast and latching-type
readout, yet requires only a small number of readout photons in the resonator
to which the qubit is coupled, thus featuring the combined advantages of
several disparate schemes. We have achieved high-fidelity, single-shot, and
non-destructive qubit readout with Rabi-oscillation contrast exceeding 90%,
limited primarily by the qubit's energy relaxation.",1407.7195v1
2014-09-24,Radiation-induced softening of Fe and Fe-based alloys during in-situ electron irradiation under mechanical testing,"Defects formed under irradiation in the bulk act as additional pinning
centers resulting in the well-known effect of radiation-induced hardening. On
the other hand, there is a poorly understood but well-established effect of
instant and reversible softening of metals subjected to various types of
irradiation. This radiation-induced softening (RIS) effect should be taken into
account both in the theory of radiation effects and in the engineering approach
for technological applications. In the present paper, the RIS is investigated
experimentally in polycrystalline technically pure iron (0.048%C) and in
commercial ferritic steel. The effect of the electron beam on plastic
deformation of bcc Fe is compared with that in fcc Al (99.5%). Electron energy
ranged from 0.5 to 0.8 MeV. Reversible drop of the yield stress and
radiation-induced reduction of the elongation to fracture are measured as
functions of the electron current and specimen thickness. Rate theory of RIS is
proposed, which takes into account the radiation-induced excitation of moving
discrete breathers (DBs), recently proven to exist in bcc Fe, and their
interaction with dislocations enhancing unpinning from structural defects. The
behavior of the DBs is studied using classical MD simulations providing input
for the modified rate theory, which eventually demonstrates a reasonable
agreement with experimental data. The relevance of results to the in-reactor
behavior of pressure vessel steels is discussed.",1409.6799v1
2015-07-27,X-ray microtomography of heavy microstructures: the case of Plasma-Sprayed Tungsten and Tungsten-Steel MMC,"In this paper synchrotron microtomography on Plasma Sprayed Tungsten (PS-W)
is presented and discussed. PS-W is a challenging material for microtomography
since it exhibits a random porous network at different length-scales (from
nanometers to micrometers) and is hardly penetrable by X-rays. Furthermore,
inner porosity causes strong internal scattering. The key challenges were,
firstly, to optimize the beam parameters considering the inherent trade-off
between photon energy (penetration depth) and spatial resolution and, secondly,
to develop effective signal filtering algorithms. Despite the limited
signal-to-noise ratio detected, large volumes of PS-W could be reconstructed
with good image quality and micrometric resolution (voxel size = 1.4 {\mu}m).
As an important result, we report excellent image quality and higher
penetration depth by applying the same setup on a ferrous microstructure,
namely a 10%W/Steel MMC used as interlayer between PS-W and a
ferritic/martensitic steel substrate. The paper reports a detailed 3D
morphological analysis of all inclusion types in PS-W and W/Steel, which led to
disclosure of a complex connected porous network in both media. The analysis is
presented in terms of multiphase volume fraction, ratio of percolation and 3D
shape descriptors. 3D percolation patterns are analyzed in detail and
sensitivity towards segmentation threshold for the noise-affected PS-W region
is discussed. Remarkably, percolation of the porous phase was found throughout
the entire coating thickness of PS-W. In W-Steel MMC percolation was found in
the perpendicular plane and interpreted as onset of delamination caused by
thermomechanical stress.",1507.07547v3
2016-10-01,Effects of biaxial strain on the improper multiferroicity in h-LuFeO3 films,"Elastic strain is potentially an important approach in tuning the properties
of the improperly multiferroic hexagonal ferrites, the details of which have
however been elusive due to the experimental difficulties. Employing the method
of restrained thermal expansion, we have studied the effect of isothermal
biaxial strain in the basal plane of h-LuFeO3 (001) films. The results indicate
that a compressive biaxial strain significantly enhances the ferrodistortion,
and the effect is larger at higher temperatures. The compressive biaxial strain
and the enhanced ferrodistortion together, cause an increase in the electric
polarization and a reduction in the canting of the weak ferromagnetic moments
in h-LuFeO3, according to our first principle calculations. These findings are
important for understanding the strain effect as well as the coupling between
the lattice and the improper multiferroicity in h-LuFeO3. The experimental
elucidation of the strain effect in h-LuFeO3 films also suggests that the
restrained thermal expansion can be a viable method to unravel the strain
effect in many other epitaxial thin film materials.",1610.00073v1
2017-03-24,Electronic structure and direct observation of ferrimagnetism in multiferroic hexagonal YbFeO3,"The magnetic interaction between rare-earth and Fe ions in hexagonal
rare-earth ferrites (h-REFeO3), may amplify the weak ferromagnetic moment on
Fe, making these materials more appealing as multiferroics. To elucidate the
interaction strength between the rare-earth and Fe ions as well as the magnetic
moment of the rare-earth ions, element specific magnetic characterization is
needed. Using X-ray magnetic circular dichroism, we have studied the
ferrimagnetism in h-YbFeO3 by measuring the magnetization of Fe and Yb
separately. The results directly show anti-alignment of magnetization of Yb and
Fe ions in h-YbFeO3 at low temperature, with an exchange field on Yb of about
17 kOe. The magnetic moment of Yb is about 1.6 \muB at low-temperature,
significantly reduced compared with the 4.5 \muB moment of a free Yb3+. In
addition, the saturation magnetization of Fe in h-YbFeO3 has a sizable
enhancement compared with that in h-LuFeO3. These findings directly demonstrate
that ferrimagnetic order exists in h-YbFeO3; they also account for the
enhancement of magnetization and the reduction of coercivity in h-YbFeO3
compared with those in h-LuFeO3 at low temperature, suggesting an important
role for the rare-earth ions in tuning the multiferroic properties of h-REFeO3.",1703.08482v2
2017-08-17,"Multiferroic Core-Shell Nanofibers, Assembly in a Magnetic field and Studies on MagnetoElectric Interactions","Ferromagnetic-ferroelectric nanocomposites are of interest for realizing
strong strain mediated coupling between electric and magnetic subsystems due to
high surface area-to-volume ratio. This report is on the synthesis of nickel
ferrite (NFO) -barium titanate (BTO) core-shell nano-fibers, magnetic field
assisted assembly into superstructures, and studies on magneto-electric (ME)
interactions. Electrospinning techniques were used to prepare coaxial fibers of
0.5-1.5 micron in diameter. The core-shell structure of annealed fibers was
confirmed by electron microscopy and scanning probe microscopy. The fibers were
assembled into discs and films in a uniform magnetic field or a field gradient.
Studies on ME coupling in the assembled films and discs were done by magnetic
field H induced polarization, magneto-dielectric effects at low frequencies and
at 16-24 GHz, and low frequency ME voltage coefficients (MEVC). We measured 2~
2-7% change in remnant polarization and in the permittivity for H = 7 kOe, and
a MEVC of 0.4 mV/cm Oe at 30 Hz. A model has been developed for low-frequency
ME effects in an assembly of fibers and takes into account dipole-dipole
interactions between the fibers and fiber discontinuity. Theoretical estimates
for the low-frequency MEVC have been compared with the data. These results
indicate strong ME coupling in superstructures of the core-shell fibers.",1708.05231v1
2020-07-08,"Probing low temperature non-equilibrium magnetic state in Co$_{2.75}$Fe$_{0.25}$O$_{4+δ}$ spinel oxide using dc magnetization, ac susceptibility and neutron diffraction experiments","The low temperature lattice structure and magnetic properties of
Co$_{2.75}$Fe$_{0.25}$O$_4$ ferrite have been investigated using experimental
results from synchrotron x-ray diffraction (SXRD), dc magnetization, ac
susceptibility, neutron diffraction and neutron depolarization techniques. The
samples have been prepared by chemical co-precipitation of the Fe and Co
nitrates solution in high alkaline medium and subsequent thermal annealing of
the precipitates in the temperature range of 200- 900 $^\circ$C. Rietveld
refinement of the SXRD patterns at room temperature indicated two-phased cubic
spinel structure for the samples annealed at temperatures 200-600 $^\circ$C.
The samples annealed at temperatures 700 $^\circ$C and 900 $^\circ$C (CF90)
have been best fitted with single phased lattice structure. Refinement of the
neutron diffraction patterns in the temperature range of 5-300 K confirmed
antiferromagnetic (AFM) Co$_3$O$_4$ and ferrimagnetic (FIM)
Co$_{2.75}$Fe$_{0.25}$O$_4$ phases for the sample annealed at 600 $^\circ$C and
single FIM phase of Co$_{2.75}$Fe$_{0.25}$O$_4$ for the CF90 sample. Magnetic
measurements have shown a non-equilibrium magnetic structure, consisting of the
high temperature FIM phase and low temperature AFM phase. The magnetic phases
are sensitive to magnetic fields, where high temperature phase is suppressed at
higher magnetic fields by enhancing the low temperature AFM phase, irrespective
of annealing temperature of the samples.",2007.03906v1
2016-11-23,Magnetometer Based On Spin Wave Interferometer,"We describe magnetic field sensor based on spin wave interferometer. Its
sensing element consists of a magnetic cross junction with four micro-antennas
fabricated at the edges. Two of these antennas are used for spin wave
excitation and two others antennas are used for the detection of the inductive
voltage produced by the interfering spin waves. Two waves propagating in the
orthogonal arms of the cross may accumulate significantly different phase
shifts depending on the magnitude and the direction of the external magnetic
field. This phenomenon is utilized for magnetic field sensing. The sensitivity
has maximum at the destructive interference condition, where a small change of
the external magnetic field results in a drastic increase of the inductive
voltage as well as the change of the output phase. We report experimental data
obtained on a micrometer scale Y3Fe2(FeO4)3 cross structure. The change of the
inductive voltage near the destructive interference point exceeds 40 dB per 1
Oe. At the same time, the phase of the output exhibit a {\pi}-phase shift
within 1 Oe. The data are collected for three different orientations of the
sensor in magnetic field at room temperature. Taking into account low thermal
noise in ferrite structures, the maximum sensitivity of spin wave magnetometer
may exceed atta Tesla. Other appealing advantages include compactness, fast
data acquisition and wide temperature operating range. The physical limits of
spin wave interferometers are also discussed.",1611.08015v1
2017-04-08,Effect of Frustrated Exchange Interactions and Spin-half Impurity on the Electronic Structure of Strongly Correlated NiFe$_{2}$O$_{4}$,"Spin-polarized density functional calculations, magnetization, and neutron
diffraction measurements are carried out to investigate the magnetic exchange
interactions and strong correlation effects in Yb substituted inverse spinel
nickel ferrite. In the pristine form, the compound is found to be a mixed
insulator under the Zaanen-Sawtazsky-Allen classification scheme as it features
both charge transfer and Mott insulator mechanism. Estimation of magnetic
exchange couplings reveals that both octahedral-octahedral and
octahedral-tetrahedral spin-spin interactions are antiferromagnetic which is
typical of a spin-frustrated triangular lattice. However, the latter is
dominant compared to the former leading to a forced parallel alignment of the
spins at the octahedral site which is in agreement with the results of neutron
diffraction measurements. The substituent Yb is found to be settled in +3
charge state, as confirmed from the XPS measurements, to behave like a
spin-half impurity carried by the localized $f_{z(x^2-y^2)}$ orbital. The
impurity $f$ spin significantly weakens the antiferromagnetic coupling with the
spins at the tetrahedral site, which explains the experimental observation of
fall in Curie temperature with Yb substitution.",1704.02454v2
2017-04-21,Strain-gradient-induced magnetic anisotropy in straight-stripe mixed-phase bismuth ferrites: An insight into flexomagnetic phenomenon,"Implementation of antiferromagnetic compounds as active elements in
spintronics has been hindered by their insensitive nature against external
perturbations which causes difficulties in switching among different
antiferromagnetic spin configurations. Electrically-controllable strain
gradient can become a key parameter to tune the antiferromagnetic states of
multiferroic materials. We have discovered a correlation between an
electrically-written straight-stripe mixed-phase boundary and an in-plane
antiferromagnetic spin axis in highly-elongated La-5%-doped BiFeO$_{3}$ thin
films by performing polarization-dependent photoemission electron microscopy in
conjunction with cluster model calculations. Model Hamiltonian calculation for
the single-ion anisotropy including the spin-orbit interaction has been
performed to figure out the physical origin of the link between the strain
gradient present in the mixed phase area and its antiferromagnetic spin axis.
Our findings enable estimation of the strain-gradient-induced magnetic
anisotropy energy per Fe ion at around 5$\times$10$^{-12}$ eV m, and provide a
new pathway towards an electric-field-induced 90$^{\circ}$ rotation of
antiferromagnetic spin axis at room temperature by flexomagnetism.",1704.06627v1
2012-04-24,Formation mechanisms and relaxation of NMR spin-echo signals excited by two arbitrary duration radio-frequency pulses in magnets,"The work is devoted to the problem of multiple signals of nuclear spin echoes
in magnets, excited by a series of radio-frequency (RF) arbitrary duration
pulses exceeding the free induction decay time. The quantum-statistical
approach based on the Liouville equation solution for the statistical operator
of system is developed for the investigation of echo-processes. The obtained
theoretical results for the number of echo signals, time moments of their
formation and their intensities are in good agreement with experiments carried
out on magnets (ferrites, ferrometals, half metals, manganites). The pointed
approach is general and could be applied to EPR and NQR, which is interesting
also for its application for remote detection of explosives and narcotics. The
application of wide RF pulses and their sequences makes it possible to
accumulate weak signals, enriches the echo-response spectrum with clearly
separated intensive lines, i.e. essentially increases the sensitivity of
apparatus and, correspondingly, the possibilities to explore the fine details
of dynamical and relaxation processes taking place in nuclear spin-systems with
sufficiently long relaxation times. The work contains also results of new
experiments on study of relaxation processes in these systems.",1204.5344v2
2014-05-27,Effect of Rhombohedral to Orthorhombic Transition on Magnetic and Dielectric Properties of La and Ti co-substituted BiFeO3,"Polycrystalline La and Ti co-substituted ceramics were synthesized by the
tartaric acid modified sol-gel technique. It was observed that the
co-substitution of La & Ti at Bi & Fe sites in BiFeO3 suppress the impurity
phase formation which is a common problem in bismuth ferrite. The quantitative
crystallographic phase analysis was performed with the help of FULLPROF program
which suggests the existence of compositional driven crystal structure
transition from rhombohederal (space group R3c) to the orthorhombic (space
group Pbnm). The changes in the phonon frequencies as well as line widths of A1
mode in Raman spectra reveal the lattice distortion which tends to modify the
crystal structure. The structural transition breaks the spin cycloid structure
in co-substituted BiFeO3 nanoparticles which leads to canting of the
antiferromagnetic spin structure. Hence, the remnant magnetization increases up
to 10 % of co-substitution and becomes 22 times that of BiFeO3. However, it
decreases for higher co-substitution percentage due to significant contribution
from the collinear antiferromagnetic ordering in the orthorhombic crystal
symmetry. The co-substitution significantly enhanced the dielectric constant
(maximum in x = 0.100) as well as frequency independent region for dielectric
constant and dielectric loss.",1405.6878v1
2015-12-18,A multiferroic on the brink: uncovering the nuances of strain-induced transitions in BiFeO$_3$,"Bismuth ferrite (BiFeO$_3$) is one of the very few known single-phase
multiferroic materials. While the bulk compound is rhombohedral (R), the
discovery of an epitaxial strain-induced structural transition into a so-called
'super tetragonal-phase' (T-phase) in this material incited a flurry of
research activity focused on gaining an understanding of this phase transition
and its possible functionalities. This metastable phase of BiFeO$_3$ is also
multiferroic, with giant ferroelectric polarization and coexisting
antiferromagnetic order, but above all it is the strain relaxation-induced
phase mixtures and their outstanding piezoelectric and magnetoelectric
responses which continue to intrigue and motivate the physicist and materials
scientist communities. Here, we review the research into the T-phase and
mixed-phase BiFeO$_3$ system. We begin with a brief summary of the history of
the T-phase and an analysis of the structure of the various phases reported in
the literature. We then address important questions regarding the symmetry and
octahedral rotation patterns and the (as yet underexplored) important role of
chemistry in the formation of the metastable T-phase. We follow by describing
the phase transitions in this material, and how these may hold promise for
large magnetoelectric responses. Finally we point out some experimental
challenges inherent to the study of such a system, and potential pathways for
how they may be overcome. It is our intention with this work to highlight
important issues that, in our opinion, should be carefully considered by the
community in order to use this fascinating materials system for a new paradigm
of functionality.",1512.05835v1
2016-05-05,"Structural, optical and complex impedance spectroscopy study of multiferroic Bi2Fe4O9 ceramic","Multiferroic bismuth ferrite Bi_2Fe_4O_9 (BFO) ceramic was synthesized by
conventional solid state reaction route. X-ray diffraction and Rietveld
refinement show formation of single phase ceramic with orthorhombic crystal
structure (space group Pbam). The morphological study depicted a well-defined
grain of size $\simeq$2{\mu}m. The optical studies were carried out by using
UV-Vis spectrophotometer which shows a band gap of 1.53 eV and a green emission
spectrum at 537 is observed in the Photoluminescence study. The frequency
dependent dielectric study at various temperature revealed that the dielectric
constant decreases with increase in frequency. A noticeable peak shift towards
higher frequency with increasing temperature is observed in the frequency
dependent dielectric loss plot. The impedance spectroscopy shows a substantial
shift in imaginary impedance (Z"") peaks toward the high frequency side
described that the conduction in material favoring the long range motion of
mobile charge carriers. The presence of non-Debye type multiple relaxations has
been confirmed by complex modulus analysis. The frequency dependent ac
conductivity at different temperatures indicates that the conduction process is
thermally activated. The variation of dc conductivity exhibited a negative
temperature coefficient of resistance behavior. The activation energy
calculated from impedance, modulus and conductivity data confirmed that the
oxygen vacancies play a vital role in the conduction mechanism.",1605.01574v1
2017-06-14,Effects of the Hubbard U on density functional-based predictions of BiFeO$_3$ properties,"First principles studies of multiferroic materials, such as bismuth ferrite
(BFO), require methods that extend beyond standard density functional theory
(DFT). The DFT+U method is one such extension that is widely used in the study
of BFO. We present a systematic study of the effects of the U parameter on the
structural, ferroelectric and electronic properties of BFO. We find that the
structural and ferroelectric properties change negligibly in the range of U
typically considered for BFO (3-5 eV). In contrast, the electronic structure
varies significantly with U. In particular, we see large changes to the
character and curvature of the valence band maximum and conduction band
minimum, in addition to the expected increase in band gap, as U increases. Most
significantly, we find that the $t_{2g}$/$e_{g}$ ordering, expected from
crystal field theory, is inverted for U values larger than 4 eV. We therefore
recommend a U value of at most 4 eV to be applied to the Fe $d$ orbitals in
BFO. More generally, this study emphasises the need for systematic
investigations of the effects of the U parameter not merely on band gaps but on
the electronic structure as a whole, especially for strongly correlated
materials.",1706.04369v2
2017-06-23,Fabrication of highly dense isotropic Nd-Fe-B bonded magnets via extrusion-based additive manufacturing,"Isotropic bonded magnets with a high loading fraction of 70 vol.% Nd-Fe-B are
fabricated via an extrusion-based additive manufacturing, or 3D printing system
that enables rapid production of large parts for the first time. The density of
the printed magnet is 5.15 g/cm3. The room temperature magnetic properties are:
intrinsic coercivity Hci = 8.9 kOe (708.2 kA/m), remanence Br = 5.8 kG (0.58
Tesla), and energy product (BH)max = 7.3 MGOe (58.1 kJ/m3). The as-printed
magnets are then coated with two types of polymers, both of which improve the
thermal stability at 127 {\deg}C as revealed by flux aging loss measurements.
Tensile tests performed at 25 {\deg}C and 100 {\deg}C show that the ultimate
tensile stress (UTS) increases with increasing loading fraction of the magnet
powder, and decreases with increasing temperature. AC magnetic susceptibility
and resistivity measurements show that the 3D printed Nd-Fe-B bonded magnets
exhibit extremely low eddy current loss and high resistivity. Finally, we show
that through back electromotive force measurements that motors installed with
3D printed Nd-Fe-B magnets exhibit similar performance as compared to those
installed with sintered ferrites.",1706.07792v1
2017-12-12,"Refutation of [Chyba and Hand, Phys. Rev. Applied 6, 014017 (2016)]: No Electric Power can be Generated from Earth's Rotation through its Own Magnetic Field","In a recent article [Phys. Rev. Applied 6, 014017 (2016)], Chyba and Hand
propose a new scheme to generate electric power continuously at the expense of
Earth's kinetic energy of rotation, by using an appropriately shaped
cylindrical shell of a well chosen conducting ferrite, rigidly attached to the
Earth. No experimental confirmation is reported for the new prediction. In the
present Refutation, I first use today's standard electromagnetism and
essentially the same model as Chyba and Hand to show in a very simple way that
no device of the proposed type can produce continuous electric power, whatever
its configuration or size, in agreement with widespread expectation. Next, I
show that the prediction of non-zero continuous power by Chyba and Hand results
from a confusion of frames of reference at a critical step of their derivation.
When the confusion is clarified, the prediction becomes exactly zero and the
article under discussion appears as pointless. At the end, I comment about the
persistent invocation by Chyba and Hand of the misleading legacy notion that
quasi-static magnetic fields have an intrinsic velocity, and other questionable
concepts.",1712.04283v4
2018-01-04,Effect of in-situ electric field assisted growth on anti-phase boundaries in epitaxial Fe3O4 thin films on MgO,"Anti-phase boundaries (APBs) normally form as a consequence of the initial
growth conditions in all spinel ferrite thin films. The presence of APBs in
epitaxial films of the inverse spinel Fe3O4 alters their electronic and
magnetic properties due to strong antiferromagnetic (AF) interactions across
these boundaries. The effect of using in-situ electric field assisted growth on
the migration of APBs in hetero epitaxial Fe3O4(100)/MgO(100) thin films have
been explored in the present work. The electric field assisted growth is found
to reduce the AF interactions across APBs and as a consequence APBs free thin
film like properties are obtained, which have been probed by electronic,
magnetic and structural characterization. An increase in energy associated with
the nucleation and/or early stage of the growth and, therefore, a corresponding
increase in surface mobility of the ad-atoms play a critical role in
controlling the density of APBs. This innovative technique can be employed to
grow epitaxial spinel thin films with controlled AF interactions across APBs.",1801.01520v1
2019-09-27,Microwave measurement beyond the quantum limit with a nonreciprocal amplifier,"The measurement of a quantum system is often performed by encoding its state
in a single observable of a light field. The measurement efficiency of this
observable can be reduced by loss or excess noise on the way to the detector.
Even a \textit{quantum-limited} detector that simultaneously measures a second
non-commuting observable would double the output noise, therefore limiting the
efficiency to $50\%$. At microwave frequencies, an ideal measurement efficiency
can be achieved by noiselessly amplifying the information-carrying quadrature
of the light field, but this has remained an experimental challenge. Indeed,
while state-of-the-art Josephson-junction based parametric amplifiers can
perform an ideal single-quadrature measurement, they require lossy ferrite
circulators in the signal path, drastically decreasing the overall efficiency.
In this paper, we present a nonreciprocal parametric amplifier that combines
single-quadrature measurement and directionality without the use of strong
external magnetic fields. We extract a measurement efficiency of $62_{-9}^{+17}
\%$ that exceeds the quantum limit and that is not limited by fundamental
factors. The amplifier can be readily integrated with superconducting devices,
creating a path for ideal measurements of quantum bits and mechanical
oscillators.",1909.12964v2
2019-10-04,"Partial time-reversal invariance violation in a flat, superconducting microwave cavity with the shape of a chaotic Africa billiard","We report on the experimental realization of a flat, superconducting
microwave resonator, a microwave billiard, with partially violated
time-reversal (T ) invariance, induced by inserting a ferrite into the cavity
and magnetizing it with an external magnetic field perpendicular to the
resonator plane. In order to prevent its expulsion caused by the
Meissner-Ochsenfeld effect we used a cavity of which the top and bottom plate
were made from niobium, a superconductor of type II, and cooled it down to
liquid-helium temperature T LHe ' 4 K. The Cavity had the shape of a chaotic
Afrivca billiard. Superconductivity rendered possible the accurate
determination of complete sequences of the resonance frequencies and of the
widths and strengths of the resonances, an indispensable prerequisite for the
unambiguous detection of T invariance violation, especially when it is only
partially violated. This allows for the first time the precise specification of
the size of T invariance violation from the fluctuation properties of the
resonance frequencies and from the strength distribution, which actually
depends sensitively on it and thus provides a most suitable measure. For this
purpose we derived an analytical expression for the latter which is valid for
isolated resonances in the range from no T invariance violation to complete
violation.",1910.04248v1
2020-03-31,Comparative study of hydrogen embrittlement resistance between additively and conventionally manufactured austenitic stainless steels,"Hydrogen embrittlement in 304L (18wt.% Cr, 8-10wt.% Ni) austenitic stainless
steel (ASS) fabricated by laser powder-bed-fusion (LPBF) was investigated by
tensile testing after electrochemical hydrogen pre-charging and compared to
conventionally available 304L ASSs with two different processing histories, (i)
casting plus annealing (CA) and (ii) CA plus thermomechanical treatment (TMT).
It was revealed that hydrogen-charging led to a significant reduction in
ductility for the CA sample, but only a small effect of hydrogen was observed
for the LPBF and CA-TMT samples. Hydrogen-assisted cracking behavior was found
to be strongly linked to strain-induced martensitic transformation. In
addition, the amount of alpha' martensite was much higher in the CA sample than
in other samples, suggesting that severe hydrogen embrittlement can be
correlated with the low mechanical stability of austenite. Detailed
microstructural characterization showed that low austenite stability of the CA
sample was mainly attributed to the retained content of delta ferrite and the
chemical inhomogeneity inside the gamma matrix (gamma close to delta has ~2
wt.% higher Cr but ~2 wt.% lower Ni), but TMT enhanced the chemical homogeneity
and thus austenite stability. By contrast, the LPBF process led directly, i.e.
without any thermomechanical treatment, to a fully austenitic structure with
homogeneous elemental distribution in the ASS. These results confirmed that the
presence of delta and the chemical inhomogeneity inside gamma matrix, which
promoted the deformation-induced martensitic transformation and the associated
H enrichment at the gamma-alpha' interface, was the primary reason for the
severe H-assisted failure.",2004.00085v1
2020-12-26,Structure and soft magnetic properties of single-domain Mg$_{1-x}$Ni$_x$Fe$_2$O$_4$ ($0 \le x \le 1.0$) nanocrystals,"The effects of Ni$^{2+}$ substitution on the structure (lattice parameters,
cations distribution, average cations radii, cation-cation/anion bond lengths
and angles) and the soft magnetic properties of Mg$_{1-x}$Ni$_x$Fe$_2$O$_4$ ($0
\le x \le 1.0$) nanocrystals have been studied by x-ray diffraction with
Rietveld refinement, transmittance electron microscopy, Mossbauer spectroscopy
and magnetization measurements. The mostly inverse spinel structure was found
in MgFe$_2$O$_4$ nanoparticles and the inversion factor is further increased by
Ni-substitution up to a complete inversion in NiFe$_2$O$_4$. The synthesized
ferrites with a small particle size (20 - 30 nm) exhibit soft magnetic
properties of a single-domain behavior with critical domain size about 30 - 40
nm. An observed monotonic increase in magnetization and drastic decrease in
coercivity at 5 K by Ni-substitution result in a lowest anisotropy constant Ku
(2.8 kJ/m3) for x = 0.5. We discuss the evolution of magnetic properties by
Ni-substitution in a correlation with a subsequent cations-redistribution
between sites of the two sublattices and corresponding structural changes in
the inter-ionic distances.",2012.13819v1
2017-11-09,Switchable Ferroelectric Photovoltaic Effects in Epitaxial Thin Films of h-RFeO3 having Narrow Optical Band Gaps,"Ferroelectric photovoltaics (FPVs) have drawn much attention owing to their
high stability, environmental safety, anomalously high photovoltages, coupled
with reversibly switchable photovoltaic responses. However, FPVs suffer from
extremely low photocurrents, which is primarily due to their wide band gaps.
Here, we present a new class of FPVs by demonstrating switchable ferroelectric
photovoltaic effects using hexagonal ferrite (h-RFeO3) thin films having narrow
band gaps of ~1.2 eV, where R denotes rare-earth ions. FPVs with narrow band
gaps suggests their potential applicability as photovoltaic and optoelectronic
devices. The h-RFeO3 films further exhibit reasonably large ferroelectric
polarizations, which possibly reduces a rapid recombination rate of the
photo-generated electron-hole pairs. The power conversion efficiency (PCE) of
h-RFeO3 thin-film devices is sensitive on the magnitude of polarization. In the
case of h-TmFeO3 (h-TFO) thin film, the measured PCE is twice as large as that
of the BiFeO3 thin film, a prototypic FPV. We have further shown that the
switchable photovoltaic effect dominates over the unswitchable internal field
effect arising from the net built-in potential. This work thus demonstrates a
new class of FPVs towards high-efficiency solar cell and optoelectronic
applications.",1711.03250v1
2018-03-12,Understanding the mechanical properties of reduced activation steels,"Reduced activation ferritic/martensitic (RAFM) steels are structural
materials with potential application in Generation-IV fission and fusion
reactors. We use density-functional theory to scrutinize the micro-mechanical
properties of the main alloy phases of three RAFM steels based on the
body-centered cubic FeCrWVMn solid solution. We assess the lattice parameters
and elastic properties of ferromagnetic $\alpha$-Fe and Fe$_{91}$Cr$_{9}$,
which are the main building blocks of the RAFM steels, and present a detailed
analysis of the calculated alloying effects of V, Cr, Mn, and W on the
mechanical properties of Fe$_{91}$Cr$_{9}$. The composition dependence of the
elastic parameters is decomposed into electronic and volumetric contributions
and studied for alloying levels that cover the typical intervals in RAFM
steels. A linear superposition of the individual solute effects on the
properties of Fe$_{91}$Cr$_{9}$ is shown to provide an excellent approximation
for the \emph{ab initio} values obtained for the RAFM steels. The intrinsic
ductility is evaluated through Rice's phenomenological theory using the surface
and unstable stacking fault energies, and the predictions are contrasted with
those obtained by empirical criteria. Alloying with V or W is found to enhance
the ductility, whereas additional Cr or Mn turns the RAFM base alloys more
brittle.",1803.04178v1
2018-03-24,Microstructural constitutive model for polycrystal viscoplasticity in cold and warm regimes based on continuum dislocation dynamics,"Viscoplastic flow of polycrystalline metallic materials is the result of
motion and interaction of dislocations, line defects of the crystalline
structure. In the microstructural (physics-based) constitutive model presented
in this paper, the main underlying microstructural processes influencing
viscoplastic deformation and mechanical properties of metals in cold and warm
regimes are statistically described by the introduced sets of postulates/axioms
for continuum dislocation dynamics (CDD). Three microstructural (internal)
state variables (MSVs) are used for statistical quantifications of different
types/species of dislocations by the notion of dislocation density. Considering
the mobility property of dislocations, they are categorized to mobile and
(relatively) immobile dislocations. Mobile dislocations carry the plastic
strain (rate), while immobile dislocations contribute to plastic hardening.
Moreover, with respect to their arrangement, dislocations are classified to
cell and wall dislocations. Cell dislocations are those that exist inside
cells/subgrains, and wall dislocations are packed in (and consequently formed)
the subgrain walls/boundaries. Therefore, the MSVs incorporated in this model
are cell mobile, cell immobile and wall immobile dislocation densities. The
evolution of these internal variables is calculated by means of adequate
equations that characterize the dislocation processes dominating material
behavior during cold and warm monotonic viscoplastic deformation. The
constitutive equations are then numerically integrated; and the constitutive
parameters are determined/fitted for a widely used ferritic-pearlitic steel
(20MnCr5).",1803.09174v3
2019-01-22,Ferromagnetic-like behavior of Bi0.9La0.1FeO3-KBr nanocomposites,"We studied magnetostatic response of the Bi0.9La0.1FeO3-KBr composites
(BLFO-KBr) consisting of nanosized (about 100 nm) ferrite Bi0.9La0.1FeO3 (BLFO)
conjugated with fine grinded ionic conducting KBr. When the fraction of KBr is
rather small (less than 15 wt percent) the magnetic response of the composite
is very weak and similar to that observed for the BLFO (pure KBr matrix without
Bi1-xLaxFeO3 has no magnetic response as anticipated). However, when the
fraction of KBr increases above 15percent, the magnetic response of the
composite changes substantially and the field dependence of magnetization
reveals ferromagnetic-like hysteresis loop with a remanent magnetization about
0.14 emu/g and coercive field about 1.8 Tesla (at room temperature). Nothing
similar to the ferromagnetic-like hysteresis loop can be observed in BLFO
ceramics, which magnetization quasi linearly increases with magnetic field.
Different physical mechanisms were considered to explain the unusual
experimental results for BLFO-KBr nanocomposites, but only those among them,
which are highly sensitive to the interaction of antiferromagnetic
Bi0.9La0.1FeO3 with ionic conductor KBr, can be relevant. An appropriate
mechanism turned out to be ferro-magneto-ionic coupling.",1901.08913v1
2019-04-05,"Stoichiometry, Phase, and Texture Evolution in PLD-Grown Hexagonal Barium Ferrite Films as a Function of Laser Process Parameters","Barium hexaferrite (BaFe12O19 or BaM) films were grown on c-plane sapphire
(0001) substrates by pulsed laser deposition (PLD) to evaluate the effects of
the laser fluence on their composition, structure, and magnetic properties.
Continuum's Surelite pulsed 266nm Nd:YAG laser was employed, and the laser
fluence varied systemically between 1 and 5.7 [J/cm2]. Deviations from the
stoichiometric transfer between the BaM targets and deposited thin films
occurred as the laser fluence changed. The Fe to Ba ratio in the films
increased with the laser fluence. The films deposited at the laser fluences
below 4 J/cm2 showed undesirable 3-dimensional islands on the surface.
Moreover, insufficient laser energy resulted in the deposition of some
secondary phases, for example, barium monoferrite (BaFe2O4) and Magnetite
(Fe3O4). On the other hand, laser fluences above 5 J/cm2 promoted resputtering
and degraded the film quality, structure, and magnetic properties. BaM films
deposited at 4.8 J/cm2 - the optimal laser fluence - showed excellent c-axis
orientation perpendicular to the film plane with the anisotropy field of 16 kOe
and saturation magnetization of 4.39 kOe. These results clearly demonstrate a
strong influence of the laser parameters on the PLD-grown hexaferrite films and
pave the path for the high-yield production using PLD systems.",1904.03157v2
2019-08-12,Rollable Magnetoelectric Energy Harvester as Wireless IoT Sensor,"Perhaps the most abundant form of waste energy in our surrounding is the
parasitic magnetic noise arising from electrical power transmission system. In
this work, a flexible and rollable magneto-mechano-electric nanogenerator
(MMENG) based wireless IoT sensor has been demonstrated in order to capture and
utilize the magnetic noise. Free standing magnetoelectric (ME) composites are
fabricated by combining magnetostrictive nickel ferrite nanoparticles and
piezoelectric polyvinylidene-co-trifluoroethylene polymer. The magnetoelectric
0-3 type nanocomposites possess maximum ME co-efficient of 11.43 mV/cm-Oe.
Even, without magnetic bias field 99 % of the maximum ME co-efficient value is
observed due to self-bias effect. As a result, the MMENG generates sufficient
peak-to-peak open circuit voltage, output power density and successfully
operates commercial capacitor under the weak and low frequency stray magnetic
field arising from the power cable of home appliances such as, electric kettle.
Finally, the harvested electrical signal has been wirelessly transmitted to a
smart phone in order to demonstrate the possibility of position monitoring
system construction. This cost effective and easy to integrate approach with
tailored size and shape of device configuration is expected to be explored in
next-generation self-powered IoT sensors including implantable biomedical
devices and human health monitoring sensory systems.",1908.04282v1
2019-11-03,Ferromagnetic dynamics detected via one- and two-magnon NV relaxometry,"The NV center in diamond has proven to be a powerful tool for locally
characterizing the magnetic response of microwave excited ferromagnets. To
date, this has been limited by the requirement that the FMR excitation
frequency be less than the NV spin resonance frequency. Here we report NV
relaxometry based on a two-magnon Raman-like process, enabling detection of FMR
at frequencies higher than the NV frequency. For high microwave drive powers,
we observe an unexpected field-shift of the NV response relative to a
simultaneous microwave absorption signal from a low damping ferrite film. We
show that the field-shifted NV response is due to a second order Suhl
instability. The instability creates a large population of non-equilibrium
magnons which relax the NV spin, even when the uniform mode FMR frequency
exceeds that of the NV spin resonance frequency, hence ruling out the
possibility that the NV is relaxed by a single NV-resonant magnon. We argue
that at high frequencies the NV response is due to a two-magnon relaxation
process in which the difference frequency of two magnons matches the NV
frequency, and at low frequencies we evaluate the lineshape of the one-magnon
NV relaxometry response using spinwave instability theory.",1911.00829v1
2019-12-09,Field Dependence of Magnetic Disorder in Nanoparticles,"The performance characteristics of magnetic nanoparticles towards
application, e.g. in medicine, imaging, or as sensors, is directly determined
by their magnetization relaxation and total magnetic moment. In the commonly
assumed picture, nanoparticles have a constant overall magnetic moment
originating from the magnetization of the single-domain particle core
surrounded by a surface region hosting spin disorder. In contrast, this work
demonstrates the significant increase of the magnetic moment of ferrite
nanoparticles with applied magnetic field. At low magnetic field, the
homogeneously magnetized particle core initially coincides in size with the
structurally coherent grain of 12.8(2) nm diameter, indicating a strong
coupling between magnetic and structural disorder. Applied magnetic fields
gradually polarize the uncorrelated, disordered surface spins, resulting in a
magnetic volume more than 20\% larger than the structurally coherent core. The
intraparticle magnetic disorder energy increases sharply towards the
defect-rich surface as established by the field-dependence of the magnetization
distribution. In consequence, these findings illustrate how the nanoparticle
magnetization overcomes structural surface disorder. This new concept of
intraparticle magnetization is deployable to other magnetic nanoparticle
systems, where the in-depth knowledge of spin disorder and associated magnetic
anisotropies will be decisive for a rational nanomaterials design.",1912.04081v2
2019-12-16,Universal spin-resolved thermal radiation laws for nonreciprocal bianisotropic media,"A chiral absorber of light can emit spin-polarized (circularly polarized)
thermal radiation based on Kirchhoff's law which equates spin-resolved
emissivity with spin-resolved absorptivity for reciprocal media at thermal
equilibrium. No such law is known for nonreciprocal media. In this work, we
discover three spin-resolved Kirchhoff's laws of thermal radiation applicable
for both reciprocal and nonreciprocal planar media. In particular, these laws
are applicable to multi-layered or composite slabs of generic bianisotropic
material classes which include (uniaxial or biaxial) birefringent crystals,
(gyrotropic) Weyl semimetals, magnetized semiconductors, plasmas, ferromagnets
and ferrites, (magnetoelectric) topological insulators, metamaterials and
multiferroic media. We also propose an experiment to verify these laws using a
single system of doped Indium Antimonide (InSb) thin film in an external
magnetic field. Furthermore, we reveal a surprising result that the planar
slabs of all these material classes can emit partially circularly polarized
thermal light without requiring any surface patterning, and identify planar
configurations which can experience nontrivial thermal optomechanical forces
and torques upon thermal emission into the external environment at lower
temperature (nonequilibrium). Our work also provides a new fundamental insight
of detailed balance of angular momentum (in addition to energy) of equilibrium
thermal radiation, and paves the way for practical functionalities based on
thermal radiation using nonreciprocal bianisotropic materials.",1912.07177v2
2020-05-04,The Newspaper Navigator Dataset: Extracting And Analyzing Visual Content from 16 Million Historic Newspaper Pages in Chronicling America,"Chronicling America is a product of the National Digital Newspaper Program, a
partnership between the Library of Congress and the National Endowment for the
Humanities to digitize historic newspapers. Over 16 million pages of historic
American newspapers have been digitized for Chronicling America to date,
complete with high-resolution images and machine-readable METS/ALTO OCR. Of
considerable interest to Chronicling America users is a semantified corpus,
complete with extracted visual content and headlines. To accomplish this, we
introduce a visual content recognition model trained on bounding box
annotations of photographs, illustrations, maps, comics, and editorial cartoons
collected as part of the Library of Congress's Beyond Words crowdsourcing
initiative and augmented with additional annotations including those of
headlines and advertisements. We describe our pipeline that utilizes this deep
learning model to extract 7 classes of visual content: headlines, photographs,
illustrations, maps, comics, editorial cartoons, and advertisements, complete
with textual content such as captions derived from the METS/ALTO OCR, as well
as image embeddings for fast image similarity querying. We report the results
of running the pipeline on 16.3 million pages from the Chronicling America
corpus and describe the resulting Newspaper Navigator dataset, the largest
dataset of extracted visual content from historic newspapers ever produced. The
Newspaper Navigator dataset, finetuned visual content recognition model, and
all source code are placed in the public domain for unrestricted re-use.",2005.01583v1
2020-06-01,Enhancement in Thermally Generated Spin Voltage at Pd/NiFe$_2$O$_4$ Interfaces by the Growth on Lattice-Matched Substrates,"Efficient spin injection from epitaxial ferrimagnetic NiFe$_2$O$_4$ thin
films into a Pd layer is demonstrated via spin Seebeck effect measurements in
the longitudinal geometry. The NiFe$_2$O$_4$ films (60 nm to 1 $\mu$m) are
grown by pulsed laser deposition on isostructural spinel MgAl$_2$O$_4$,
MgGa$_2$O$_4$, and CoGa$_2$O$_4$ substrates with lattice mismatch varying
between 3.2% and 0.2%. For the thinner films ($\leq$ 330 nm), an increase in
the spin Seebeck voltage is observed with decreasing lattice mismatch, which
correlates well with a decrease in the Gilbert damping parameter as determined
from ferromagnetic resonance measurements. High resolution transmission
electron microscopy studies indicate substantial decrease of antiphase boundary
and interface defects that cause strain-relaxation, i.e., misfit dislocations,
in the films with decreasing lattice mismatch. This highlights the importance
of reducing structural defects in spinel ferrites for efficient spin injection.
It is further shown that angle-dependent spin Seebeck effect measurements
provide a qualitative method to probe for in-plane magnetic anisotropies
present in the films.",2006.00777v1
2020-08-09,Efficient and Low-Backaction Quantum Measurement Using a Chip-Scale Detector,"Superconducting qubits are a leading platform for scalable quantum computing
and quantum error correction. One feature of this platform is the ability to
perform projective measurements orders of magnitude more quickly than qubit
decoherence times. Such measurements are enabled by the use of quantum-limited
parametric amplifiers in conjunction with ferrite circulators - magnetic
devices which provide isolation from noise and decoherence due to amplifier
backaction. Because these non-reciprocal elements have limited performance and
are not easily integrated on-chip, it has been a longstanding goal to replace
them with a scalable alternative. Here, we demonstrate a solution to this
problem by using a superconducting switch to control the coupling between a
qubit and amplifier. Doing so, we measure a transmon qubit using a single,
chip-scale device to provide both parametric amplification and isolation from
the bulk of amplifier backaction. This measurement is also fast, high fidelity,
and has 70% efficiency, comparable to the best that has been reported in any
superconducting qubit measurement. As such, this work constitutes a
high-quality platform for the scalable measurement of superconducting qubits.",2008.03805v2
2020-08-22,High-Performance Thermoelectric Oxides Based on Spinel Structure,"High-performance thermoelectric oxides could offer a great energy solution
for integrated and embedded applications in sensing and electronics industries.
Oxides, however, often suffer from low Seebeck coefficient when compared with
other classes of thermoelectric materials. In search of high-performance
thermoelectric oxides, we present a comprehensive density functional
investigation, based on GGA$+U$ formalism, surveying the 3d and 4d
transition-metal-containing ferrites of the spinel structure. Consequently, we
predict MnFe$_2$O$_4$ and RhFe$_2$O$_4$ have Seebeck coefficients of $\sim \pm
600$ $\mu$V K$^{-1}$ at near room temperature, achieved by light hole and
electron doping. Furthermore, CrFe$_2$O$_4$ and MoFe$_2$O$_4$ have even higher
ambient Seebeck coefficients at $\sim \pm 700$ $\mu$V K$^{-1}$. In the latter
compounds, the Seebeck coefficient is approximately a flat function of
temperature up to $\sim 700$ K, offering a tremendous operational convenience.
Additionally, MoFe$_2$O$_4$ doped with $10^{19}$ holes/cm$^3$ has a calculated
thermoelectric power factor of $689.81$ $\mu$W K$^{-2}$ m$^{-1}$ at $300$ K,
and $455.67$ $\mu$W K$^{-2}$ m$^{-1}$ at $600$ K. The thermoelectric properties
predicted here can bring these thermoelectric oxides to applications at lower
temperatures traditionally fulfilled by more toxic and otherwise burdensome
materials.",2008.09759v1
2020-09-28,How T-invariance violation leads to an enhanced backscattering with increasing openness of a wave-chaotic system,"We report on the experimental investigation of the dependence of the elastic
enhancement, i.e., enhancement of scattering in backward direction over
scattering in other directions of a wave-chaotic system with partially violated
time-reversal (T ) invariance on its openness. The elastic enhancement factor
is a characteristic of quantum chaotic scattering which is of particular
importance in experiments, like compound-nuclear reactions, where only cross
sections, i.e., the moduli of the associated scattering matrix elements are
accessible. In the experiment a quantum billiard with the shape of a quarter
bow-tie, which generates a chaotic dynamics, is emulated by a flat microwave
cavity. Partial T-invariance violation of varying strength 0 < xi < 1 is
induced by two magnetized ferrites. The openness is controlled by increasing
the number M of open channels, 2 < M < 9, while keeping the internal absorption
unchanged. We investigate the elastic enhancement as function of xi and find
that for a fixed M it decreases with increasing time-reversal invariance
violation, whereas it increases with increasing openness beyond a certain value
of xi > 0.2. The latter result is surprising because it is opposite to that
observed in systems with preserved T invariance (xi = 0). We come to the
conclusion that the effect of T -invariance violation on the elastic
enhancement then dominates over the openness, which is crucial for experiments
which rely on enhanced backscattering, since, generally, a decrease of the
openness is unfeasible. Motivated by these experimental results we,
furthermore, performed theoretical investigations based on random matrix theory
which confirm our findings.",2009.13519v1
2020-11-13,Magnetoelectric coupling and decoupling in multiferroic hexagonal YbFeO3 thin films,"The coupling between ferroelectric and magnetic orders in multiferroic
materials and the nature of magnetoelectric (ME) effects are enduring
experimental challenges. In this work, we have studied the response of
magnetization to ferroelectric switching in thin-film hexagonal YbFeO3, a
prototypical improper multiferroic. The bulk ME decoupling and potential
domain-wall ME coupling were revealed using x-ray magnetic circular dichroism
(XMCD) measurements with in-situ ferroelectric polarization switching. Our
Landau theory analysis suggests that the bulk ME-coupled ferroelectric
switching path has a higher energy barrier than that of the ME-decoupled path;
this extra barrier energy is also too high to be reduced by the magneto-static
energy in the process of breaking single magnetic domains into multi-domains.
In addition, the reduction of magnetization around the ferroelectric domain
walls predicted by the Landau theory may induce the domain-wall ME coupling in
which the magnetization is correlated with the density of ferroelectric domain
walls. These results provide important experimental evidence and theoretical
insights into the rich possibilities of ME couplings in hexagonal ferrites,
such as manipulating the magnetic states by an electric field.",2011.07154v1
2021-03-20,Towards Superior High Temperature Properties in Low Density AlCrFeNiTi Compositionally Complex Alloys,"Three novel precipitation strengthened bcc alloys which exhibit a smooth
microstructural gradient with composition have been fabricated in bulk form by
induction casting. All three alloys are comprised of a mixture of disordered
A2-(Fe, Cr) and L2$_1$-ordered (Ni, Fe)$_{2}$AlTi type phases both as-cast and
after long-term annealing at 900 $^{\circ}$C. The ratio of disordered to
ordered phase, primary dendrite fraction, and overall microstructural
coarseness all decrease as Cr is replaced by Al and Ti. Differences in phase
composition are quantified through domain averaged principal component analysis
of energy dispersive spectroscopy data obtained during scanning transmission
electron microscopy. Bulk tensile testing reveals retained strengths of nearly
250 MPa up to 900 $^{\circ}$C for the alloys which contain a nanoscale
maze-like arrangement of ordered and disordered phases. One alloy, containing a
duplex microstructure with ductile dendritic regions and highly creep resistant
interdendritic regions, shows a promising balance between high temperature
ductility and strength. For this alloy, tension creep testing was carried out
at 700, 750, and 800 $^{\circ}$C for a broad range of loading conditions and
revealed upper bound creep rates which surpass similar ferritic superalloys and
rival those of several conventionally employed high temperature structural
alloys, including Inconel 617 and 718, at much lower density and raw material
cost.",2103.11173v1
2021-04-15,Morphotropic Phase Boundary in Sm-Substituted BiFeO3 Ceramics: Local vs Microscopic Approaches,"Samarium substituted bismuth ferrite (BiFeO3) ceramics prepared by sol-gel
synthesis method were studied using both local scale and microscopic
measurement techniques in order to clarify an evolution of the crystal
structure of the compounds across the morphotropic phase boundary region. X-ray
diffraction analysis, transmission and scanning electron microscopies, XPS,
EDS/EDX experiments and piezoresponse force microscopy were used to study the
structural transitions from the polar active rhombohedral phase to the
anti-polar orthorhombic phase and then to the non-polar orthorhombic phase,
observed in the Bi1-xSmxFeO3 compounds within the concentration range of 0.08 <
x < 0.2. The results obtained by microscopic techniques testify that the
compounds in the range of 0.12 < x < 0.15 are characterized by two phase
structural state formed by a coexistence of the rhombohedral and the anti-polar
orthorhombic phases; two phase structural state observed in the compounds with
0.15 < x < 0.18 is associated with a coexistence of the anti-polar orthorhombic
and the non-polar orthorhombic phases. Local scale measurements have revealed a
notable difference in the concentration range ascribed to the morphotropic
phase boundary estimated by microscopic measurements, the obtained results
testify a wider concentration range ascribed to a coexistence of different
structural phases, the background of the mentioned difference is discussed.",2104.07401v1
2021-04-18,Impact of particle size on the magnetic properties of highly crystalline Yb3+ substituted Ni-Zn nanoferrites,"Yb-substituted Ni-Zn ferrites have been synthesized using sol-gel auto
combustion method. The structural characterization of the compositions has been
performed by X-ray diffraction analysis, field emission scanning electron
microscopy (FESEM), quantum design physical properties measurement system
(PPMS). That ensured the formation of single phase cubic spinel structure.
Crystallite and average grain size are calculated and found to decrease with
increasing Yb3+ contents. Saturation magnetization and Bohr magnetic moment
decrease while the coercivity increases with the increase in Yb3+ contents
successfully explained by the Neels collinear two sub-lattice model and
critical size effect, respectively. Critical particle size has been estimated
at 6.4 nm, the transition point between single domain regime (below the
critical size) and multi-domain regime (beyond the critical size). Curie
temperature reduces due to the weakening of A-O-B super exchange interaction
and redistribution of cations, confirmed by the M-T graph. The compositions
retain ferromagnetic ordered structured below Curie temperature and above Curie
temperature, it becomes paramagnetic, making them plausible candidates for high
temperature magnetic device applications. The relative quality factor peak is
obtained at a very high frequency, indicating the compositions could also be
applicable for high frequency magnetic device applications.",2104.08694v1
2021-05-20,Evolution of topological defects at two sequential phase transitions of Nd2SrFe2O7,"How topological defects, unavoidable at symmetry-breaking phase transitions
in a wide range of systems, evolve through consecutive phase transitions with
different broken symmetries remains unexplored. Nd2SrFe2O7, a bilayer ferrite,
exhibits two intriguing structural phase transitions and dense networks of the
so-called type-II Z8 structural vortices at room temperature, so it is an ideal
system to explore the topological defect evolution. From our extensive
experimental investigation, we demonstrate that the cooling rate at the
second-order transition (1290oC) plays a decisive role in determining the
vortex density at room temperature, following the universal Kibble-Zurek
mechanism. In addition, we discovered a transformation between
topologically-distinct vortices (Z8 to Z4 vortices) at the first-order
transition (550oC), which conserves the number of vortex cores. Remarkably, the
Z4 vortices consist of two phases with an identical symmetry but two distinct
magnitudes of an order parameter. Furthermore, when lattice distortion is
enhanced by chemical doping, a new type of topological defects emerges: loop
domain walls with orthorhombic distortions in the tetragonal background,
resulting in unique pseudo-orthorhombic twins. Our findings open a new avenue
to explore the evolution of topological defects through multiple phase
transitions.",2105.09669v1
2021-07-19,Deformation Behaviour of Ion-Irradiated FeCr: A Nanoindentation Study,"Understanding the mechanisms of plasticity in structural steels is essential
for the operation of next-generation fusion reactors. Elemental composition,
particularly the amount of Cr present, and irradiation can have separate and
synergistic effects on the mechanical properties of ferritic/martensitic
steels. The study of ion-irradiated FeCr alloys is useful for gaining a
mechanistic understanding of irradiation damage in steels. Previous studies of
ion-irradiated FeCr did not clearly distinguish between the nucleation of
dislocations to initiate plasticity, and their propagation through the material
as plasticity progresses.
  In this study, Fe3Cr, Fe5Cr, and Fe10Cr were irradiated with 20 MeV Fe$^{3+}$
ions at room temperature to nominal doses of 0.01 dpa and 0.1 dpa.
Nanoindentation was carried out with Berkovich and spherical indenter tips to
study the nucleation of dislocations and their subsequent propagation. The
presence of irradiation-induced defects reduced the theoretical shear stress
and barrier for dislocation nucleation. The presence of Cr further enhanced
this effect due to increased retention of irradiation defects. However, this
combined effect is still small compared to dislocation nucleation from
pre-existing sources such as Frank-Read sources and grain boundaries. The yield
strength, an indicator of dislocation mobility, of FeCr increased with
irradiation damage and Cr. The increased retention of irradiation defects due
to the presence of Cr also further increased the yield strength. Reduced work
hardening capacity was also observed following irradiation. The synergistic
effects of Cr and irradiation damage in FeCr appear to be more important for
the propagation of dislocations, rather than their nucleation.",2107.09040v1
2021-09-14,Design of a HOM-Damped 166.6 MHz Compact Quarter-Wave beta=1 Superconducting Cavity for High Energy Photon Source,"Superconducting cavities with low RF frequencies and heavy damping of higher
order modes (HOM) are desired for the main accelerator of High Energy Photon
Source (HEPS), a 6 GeV synchrotron light source promising ultralow emittance
currently under construction in Beijing. A compact 166.6 MHz superconducting
cavity was proposed adopting a quarter-wave beta=1 geometry. Based on the
successful development of a proof-of-principle cavity, a HOM-damped 166.6 MHz
compact superconducting cavity was subsequently designed. A ferrite damper was
installed on the beam pipe to reduce HOM impedance below the stringent
threshold of coupled-bunch instabilities. Being compact, RF field heating on
the cavity vacuum seal was carefully examined against quenching the NbTi
flange. The cavity was later dressed with a helium vessel and the tuning
mechanism was also realized. Excellent RF and mechanical properties were
eventually achieved. Finally, the two-cavity string was designed to ensure
smooth transitions among components and proper shielding of synchrotron light.
This paper presents a complete design of a fully dressed HOM-damped
low-frequency beta=1 superconducting cavity for HEPS.",2109.06560v1
2022-01-26,"Co-substituted BiFeO3: electronic, ferroelectric, and thermodynamic properties from first principles","Bismuth ferrite, BiFeO3, is a multiferroic solid that is attracting
increasing attention as a potential photocatalytic material, because the
ferroelectric polarisation enhances the separation of photogenerated carriers.
With the motivation of finding routes to engineer the band gap and the band
alignment, while conserving or enhancing the ferroelectric properties, we have
investigated the thermodynamic, electronic and ferroelectric properties of
BiCoxFe1 xO3 solid solutions, with 0 < x < 0.13, using density functional
theory. We show that the band gap can be reduced from 2.9 eV to 2.1 eV by
cobalt substitution, while simultaneously increasing the spontaneous
polarisation, which is associated with a notably larger Born effective charge
of Co compared to Fe cations. We discuss the interaction between Co impurities,
which is strongly attractive and would drive the aggregation of Co, as
evidenced by Monte Carlo simulations. Phase separation into a Co-rich phase is
therefore predicted to be thermodynamically preferred, and the homogeneous
solid solution can only exist in metastable form, protected by slow cation
diffusion kinetics. Finally, we discuss the band alignment of pure and
Co-substituted BiFeO3 with relevant redox potentials, in the context of its
applicability in photocatalysis.",2201.11161v2
2022-02-08,Kinetic Monte Carlo Modelling of Nano-oxide Precipitation and its Associated Stability under Neutron Irradiation for the Fe-Ti-Y-O system,"While developing nuclear materials, predicting their behavior under long-term
irradiation regimes spanning decades poses a significant challenge. We
developed a novel Kinetic Monte Carlo (KMC) model to explore the precipitation
behavior of Y-Ti-O oxides along grain boundaries within nanostructured ferritic
alloys (NFA). This model also assessed the response of the oxides to neutron
irradiation, even up simulated radiation damage levels in the desired long dpa
range for reactor components. Our simulations investigated how temperature and
grain boundary sinks influenced the oxide characteristics of a 12YWT-like alloy
during heat treatments at 1023 K, 1123 K, and 1223 K. The oxide characteristics
observed in our simulations were in good agreement with existing literature.
Furthermore, the impact of grain boundaries on precipitation was found to be
minimal. The resulting oxide configurations and positions were used in
subsequent simulations that exposed them to simulated neutron irradiation to a
total accumulated dose of 8 dpa at three temperatures: 673 K, 773 K, and 873 K,
and at dose rates of 10^(-3), 10^(-4), and 10^(-5) dpa/s. This demonstrated the
expected inverse relationship between oxide size and dose rate. In a long-term
irradiation simulation at 873 K and 10^(-3) dpa/s was taken out to 66 dpa and
found the oxides in the vicinity of the grain boundary were more susceptible to
dissolution. Additionally, we conducted irradiation simulations of a 14YWT-like
alloy to reproduce findings from neutron irradiation experiments. The larger
oxides in the 14YWT-like alloy did not dissolve and displayed stability similar
to the experimental results.",2202.03641v3
2022-02-18,Synergism between B and Nb improves fire resistance in microalloyed steels,"The development of new fire-resistant steels represents a challenge in
materials science and engineering of utmost importance. Alloying elements such
as Nb and Mo are generally used to improve the strength at both room- and
high-temperatures due to, for example, the formation of precipitates and harder
microconstituents. In this study we show alternatively that the addition of
small amounts of boron in Nb-microalloyed steels may play a crucial role in
maintaining the mechanical properties at high temperatures. The 66\,\%
yield-strength criteria for fire resistance is achieved at $\approx
574$\,{\deg}C for a boron steel, whereas without boron this value reaches
$\approx 460$\,{\deg}C, a remarkable boron-induced mechanical strengthening
enhancement. DFT calculations show that boron additions can lower the vacancy
formation energy when compared to pure ferrite and, for Nb-B steels, there is a
further 24\,\% reduction, suggesting that the boron-niobium combination acts as
an effective pinning-based strengthening agent.",2202.09197v1
2022-04-25,Multiscale modelling in nuclear ferritic steels: from nano-sized defects to embrittlement,"Radiation-induced embrittlement of nuclear steels is one of the main limiting
factors for safe long-term operation of nuclear power plants. In support of
accurate and safe reactor pressure vessel (RPV) lifetime assessments, we
developed a physics-based model that predicts RPV steel hardening and
subsequent embrittlement as a consequence of the formation of nano-sized
clusters of minor alloying elements. This model is shown to provide reliable
assessments of embrittlement for a very wide range of materials, with higher
accuracy than industrial correlations. The core of our model is a multiscale
modelling tool that predicts the kinetics of solute clustering, given the steel
chemical composition and its irradiation conditions. It is based on the
observation that the formation of solute clusters ensues from atomic transport
driven by radiation-induced mechanisms, differently from classical
nucleation-and-growth theories. We then show that the predicted information
about solute clustering can be translated into a reliable estimate for
radiation-induced embrittlement, via standard hardening laws based on the
dispersed barrier model. We demonstrate the validity of our approach by
applying it to hundreds of nuclear reactors vessels from all over the world.",2204.11441v1
2022-05-17,Predicting failure characteristics of structural materials via deep learning based on nondestructive void topology,"Accurate predictions of the failure progression of structural materials is
critical for preventing failure-induced accidents. Despite considerable
mechanics modeling-based efforts, accurate prediction remains a challenging
task in real-world environments due to unexpected damage factors and defect
evolutions. Here, we report a novel method for predicting material failure
characteristics that uniquely combines nondestructive X-ray computed tomography
(X-CT), persistent homology (PH), and deep multimodal learning (DML). The
combined method exploits the microstructural defect state at the time of
material examination as an input, and outputs the failure-related properties.
Our method is demonstrated to be effective using two types of fracture datasets
(tensile and fatigue datasets) with ferritic low alloy steel as a
representative structural material. The method achieves a mean absolute error
(MAE) of 0.09 in predicting the local strain with the tensile dataset and an
MAE of 0.14 in predicting the fracture progress with the fatigue dataset. These
high accuracies are mainly due to PH processing of the X-CT images, which
transforms complex and noisy three-dimensional X-CT images into compact
two-dimensional persistence diagrams that preserve key topological features
such as the internal void size, density, and distribution. The combined PH and
DML processing of 3D X-CT data is our unique approach enabling reliable failure
predictions at the time of material examination based on void topology
progressions, and the method can be extended to various nondestructive failure
tests for practical use.",2205.09075v1
2022-07-31,Interface Engineering Enabled Low Temperature Growth of Magnetic Insulator on Topological Insulator,"Combining topological insulators (TIs) and magnetic materials in
heterostructures is crucial for advancing spin-based electronics. Magnetic
insulators (MIs) can be deposited on TIs using the spin-spray process, which is
a unique non-vacuum, low-temperature growth process. TIs have highly reactive
surfaces that oxidize upon exposure to atmosphere, making it challenging to
grow spin-spray ferrites on TIs. In this work, it is demonstrated that a thin
titanium capping layer on TI, followed by oxidation in atmosphere to produce a
thin TiOx interfacial layer, protects the TI surface, without significantly
compromising spin transport from the magnetic material across the TiOx to the
TI surface states. First, it was demonstrated that in Bi2Te3/TiOx/Ni80Fe20
heterostructures that TiOx provided an excellent barrier against diffusion of
magnetic species, yet maintained a large spin-pumping effect. Second, the TiOx
was also used as a protective capping layer on Bi2Te3, followed by the
spin-spray growth of the MI, NixZnyFe2O4 (NZFO). For the thinnest TiOx
barriers, Bi2Te3/TiOx/NZFO samples had AFM disordered interfacial layer because
of diffusion. With increasing TiOx barrier thickness, the diffusion was
reduced, but still maintained strong interfacial spin-pumping interaction.
These experimental results demonstrate a novel method of low-temperature growth
of magnetic insulators on TIs enabled by interface engineering.",2208.00499v1
2022-08-09,Hybrid spin Hall nano-oscillators based on ferromagnetic metal/ferrimagnetic insulator heterostructures,"Spin-Hall nano-oscillators (SHNOs) are promising spintronic devices to
realize current controlled GHz frequency signals in nanoscale devices for
neuromorphic computing and creating Ising systems. However, traditional SHNOs
-- devices based on transition metals -- have high auto-oscillation threshold
currents as well as low quality factors and output powers. Here we demonstrate
a new type of hybrid SHNO based on a permalloy (Py) ferromagnetic-metal
nanowire and low-damping ferrimagnetic insulator, in the form of epitaxial
lithium aluminum ferrite (LAFO) thin films. The superior characteristics of
such SHNOs are associated with the excitation of larger spin-precession angles
and volumes. We further find that the presence of the ferrimagnetic insulator
enhances the auto-oscillation amplitude of spin-wave edge modes, consistent
with our micromagnetic modeling. This hybrid SHNO expands spintronic
applications, including providing new means of coupling multiple SHNOs for
neuromorphic computing and advancing magnonics.",2208.04539v2
2022-09-20,Modeling of 3D Printable Electrical Machineries Ferromagnetic Parts,"The electrical machinery core is formed with a ferromagnetic material that
offers high magnetic properties. As ferromagnetic materials have high relative
magnetic permeability, they are important in the formation of electromagnetic
device cores. Conventional subtractive and powder metallurgy methods for
fabrication electrical machineries offer significant core losses and reduce
magnetic flux density and magnetic permeability. With the advancement of
technology, the limitation of the traditional process can be overcome by using
the additive manufacturing process. Hence, this paper proposes a 3D printable
model of two types of single-phase transformers, referred to as E-I shape and
U-I shape transformers respectively. Possibilities of designing the electrical
machinery part which has a ferromagnetic core are investigated. The efficiency
of the transformers is evaluated in terms of magnetic flux density distribution
and volumetric loss density based on the results of a large number of Finite
element simulation methods under various operating situations on COMSOL. The
performance of various ferromagnetic materials such as Soft Iron (Fe) and
Ferrite (Fe2O3) on the transformer core is evaluated. This analysis reveals
that if U-I shaped transformer can be made from 3D printing, it will be the
best feasible structure for higher operating frequency.",2209.09894v1
2022-11-06,Cementron: Machine Learning the Constituent Phases in Cement Clinker from Optical Images,"Cement is the most used construction material. The performance of cement
hydrate depends on the constituent phases, viz. alite, belite, aluminate, and
ferrites present in the cement clinker, both qualitatively and quantitatively.
Traditionally, clinker phases are analyzed from optical images relying on a
domain expert and simple image processing techniques. However, the
non-uniformity of the images, variations in the geometry and size of the
phases, and variabilities in the experimental approaches and imaging methods
make it challenging to obtain the phases. Here, we present a machine learning
(ML) approach to detect clinker microstructure phases automatically. To this
extent, we create the first annotated dataset of cement clinker by segmenting
alite and belite particles. Further, we use supervised ML methods to train
models for identifying alite and belite regions. Specifically, we finetune the
image detection and segmentation model Detectron-2 on the cement microstructure
to develop a model for detecting the cement phases, namely, Cementron. We
demonstrate that Cementron, trained only on literature data, works remarkably
well on new images obtained from our experiments, demonstrating its
generalizability. We make Cementron available for public use.",2211.03223v1
2022-12-16,Wideband Josephson Parametric Isolator,"The cryogenic hardware required to build a superconducting qubit based
quantum computer demands a variety of microwave components. These elements
include microwave couplers, filters, amplifiers, and circulators/isolators.
Traditionally implemented as discrete components, integration of this
peripheral hardware, in an effort to reduce overall footprint, thermal load,
and added noise, is a key challenge to scaling modern quantum processors with
qubit counts climbing over the 100+ mark. Ferrite--based microwave isolators,
generally employed in the readout chain to decouple qubits and resonators from
readout electronics, persist as one of the volumetrically largest devices still
utilized as discrete components. Here we present an alternative two--port
isolating integrated circuit derived from the DC Superconducting Quantum
Interference Device (DC-SQUID). Non-reciprocal transmission is achieved using
the three-wave microwave mixing properties of a flux-modulated DC--SQUID. We
show that when multiple DC-SQUIDs are embedded in a multi--pole admittance
inverting filter structure, the three-wave mixing derived from the flux pumping
of the DC-SQUIDs can provide directional microwave power flow. For a
three--pole filter device, we experimentally demonstrate a directionality
greater than 15 dB over a 600 MHz bandwidth.",2212.08563v3
2023-02-05,Origin of magnetically dead layers in spinel ferrites $M\text{Fe}_2\text{O}_4$ grown on $\text{Al}_2\text{O}_3$: Effects of post-deposition annealing studied by XMCD,"We study the electronic and magnetic states of as-grown and annealed
$M\text{Fe}_2\text{O}_4$(111)/$\text{Al}_2\text{O}_3$(111) ($M=\text{Co, Ni}$)
thin films with various thicknesses grown on Si(111) substrates with the
$\gamma$-$\text{Al}_2\text{O}_3$(111) buffer layers by using x-ray absorption
spectroscopy (XAS) and x-ray magnetic circular dichroism (XMCD), to investigate
magnetically dead layers in these films. Although the magnetically dead layers
in the as-grown samples are formed near the interface with the
$\text{Al}_2\text{O}_3$ buffer layer, we reveal that ferrimagnetic order is
partially recovered by post-deposition annealing at 973 K for 48 hours in air.
By analyzing the line shapes of the XAS and XMCD spectra, we conclude that, in
the dead layers, there are a significant number of vacancies at the $T_d$ sites
of the spinel structure, which may be the microscopic origin of the degraded
ferrimagnetic order in the $M\text{Fe}_2\text{O}_4$(111) thin films.",2302.02322v1
2023-06-19,Transition between radial and toroidal orders in a trimer-based magnetic metasurface,"The change in the arrangement of magnetic dipole moments in a magnetic
metasurface, due to the influence of an external static magnetic field, is
discussed. Each meta-atom of the metasurface is composed of three identical
disk-shaped resonators (trimer) made of magnetically saturated ferrite. To
provide physical insight, full-wave numerical simulations of the near-fields
and transmission characteristics of the metasurface are complemented by the
theoretical description based on the multipole decomposition method. With these
methods, the study of eigenmodes and scattering conditions of a single magnetic
resonator, trimer, and their array forming the metasurface is performed. It is
found that the magnetic dipole-based collective hybrid mode of the trimer can
be gradually transformed from the radial (pseudomonopole) to azimuthal
(toroidal) order and vice versa by varying the bias magnetic field strength.
This is because the magnetic dipole moment of each individual disk constituting
the trimer undergoes rotation as the bias magnetic field strength changes. This
transition between two orders is accompanied by various patterns of
localization of the electric field inside the meta-atoms. Due to the unique
field configuration of these modes, the proposed metasurface can be considered
for designing magnetic field sensors and nonreciprocal devices.",2306.10776v2
2023-06-19,Ion Intercalation in Lanthanum Strontium Ferrite for Aqueous Electrochemical Energy Storage Devices,"Ion intercalation of perovskite oxides in liquid electrolytes is a very
promising method for controlling their functional properties while storing
charge, which opens the potential application in different energy and
information technologies. Although the role of defect chemistry in the oxygen
intercalation in a gaseous environment is well established, the mechanism of
ion intercalation in liquid electrolytes at room temperature is poorly
understood. In this study, the defect chemistry during ion intercalation of
La0.5Sr0.5FeO3-{\delta} thin films in alkaline electrolytes is studied. Oxygen
and proton intercalation into the LSF perovskite structure is observed at
moderate electrochemical potentials (0.5 V to -0.4 V), giving rise to a change
in the oxidation state of Fe (as a charge compensation mechanism). The
variation of the concentration of holes as a function of the intercalation
potential was characterized by in-situ ellipsometry and the concentration of
electron holes was indirectly quantified for different electrochemical
potentials. Finally, a dilute defect chemistry model that describes the
variation of defect species during ionic intercalation was developed.",2306.10887v1
2023-07-07,Dispersive Non-reciprocity between a Qubit and a Cavity,"The dispersive interaction between a qubit and a cavity is ubiquitous in
circuit and cavity quantum electrodynamics. It describes the frequency shift of
one quantum mode in response to excitations in the other, and in closed systems
is necessarily bidirectional, i.e.~reciprocal. Here, we present an experimental
study of a non-reciprocal dispersive-type interaction between a transmon qubit
and a superconducting cavity, arising from a common coupling to dissipative
intermediary modes with broken time reversal symmetry. We characterize the
qubit-cavity dynamics, including asymmetric frequency pulls and photon
shot-noise dephasing, under varying degrees of non-reciprocity by tuning the
magnetic field bias of a ferrite component in situ. Furthermore, we show that
the qubit-cavity dynamics is well-described in a wide parameter regime by a
simple non-reciprocal master-equation model, which provides a compact
description of the non-reciprocal interaction without requiring a full
understanding of the complex dynamics of the intermediary system. Our result
provides an example of quantum non-reciprocal phenomena beyond the typical
paradigms of non-Hermitian Hamiltonians and cascaded systems.",2307.05298v3
2023-08-01,Dose and compositional dependence of irradiation-induced property change in FeCr,"Ferritic/martensitic steels will be used as structural components in next
generation nuclear reactors. Their successful operation relies on an
understanding of irradiation-induced defect behaviour in the material. In this
study, Fe and FeCr alloys (3-12%Cr) were irradiated with 20 MeV Fe-ions at 313
K to doses ranging between 0.00008 dpa to 6.0 dpa. This dose range covers six
orders of magnitude, spanning low, transition and high dose regimes. Lattice
strain and hardness in the irradiated material were characterised with
micro-beam Laue X-ray diffraction and nanoindentation, respectively.
  Irradiation hardening was observed even at very low doses (0.00008 dpa) and
showed a monotonic increase with dose up to 6.0 dpa. Lattice strain
measurements of samples at 0.0008 dpa allow the calculation of equivalent
Frenkel pair densities and corrections to the Norgett-Robinson-Torrens (NRT)
model for Fe and FeCr alloys at low dose. NRT efficiency for FeCr is 0.2, which
agrees with literature values for high irradiation energy. Lattice strain
increases up to 0.8 dpa and then decreases when the damage dose is further
increased. The strains measured in this study are lower and peak at a larger
dose than predicted by atomistic simulations. This difference can be explained
by taking temperature and impurities into account.",2308.00771v2
2023-09-24,Approaching Ferrite-Based Exchange-Coupled Nanocomposites as Permanent Magnets,"During the past decade, CoFe2O4 (hard)/Co-Fe alloy (soft) magnetic
nanocomposites have been routinely prepared by partial reduction of CoFe2O4
nanoparticles. Monoxide (i.e., FeO or CoO) has often been detected as a
byproduct of the reduction, although it remains unclear whether the formation
of this phase occurs during the reduction itself or at a later stage. Here, a
novel reaction cell was designed to monitor the reduction in situ using
synchrotron powder X-ray diffraction (PXRD). Sequential Rietveld refinements of
the in situ data yielded time-resolved information on the sample composition
and confirmed that the monoxide is generated as an intermediate phase. The
macroscopic magnetic properties of samples at different reduction stages were
measured by means of vibrating sample magnetometry (VSM), revealing a magnetic
softening with increasing soft phase content, which was too pronounced to be
exclusively explained by the introduction of soft material in the system. The
elemental compositions of the constituent phases were obtained from joint
Rietveld refinements of ex situ high-resolution PXRD and neutron powder
diffraction (NPD) data. It was found that the alloy has a tendency to emerge in
a Co-rich form, inducing a Co deficiency on the remaining spinel phase, which
can explain the early softening of the magnetic material.",2309.13729v1
2023-09-26,Multiferroic Magnon Spin-Torque Based Reconfigurable Logic-In-Memory,"Magnons, bosonic quasiparticles carrying angular momentum, can flow through
insulators for information transmission with minimal power dissipation.
However, it remains challenging to develop a magnon-based logic due to the lack
of efficient electrical manipulation of magnon transport. Here we present a
magnon logic-in-memory device in a spin-source/multiferroic/ferromagnet
structure, where multiferroic magnon modes can be electrically excited and
controlled. In this device, magnon information is encoded to ferromagnetic bits
by the magnon-mediated spin torque. We show that the ferroelectric polarization
can electrically modulate the magnon spin-torque by controlling the
non-collinear antiferromagnetic structure in multiferroic bismuth ferrite thin
films with coupled antiferromagnetic and ferroelectric orders. By manipulating
the two coupled non-volatile state variables (ferroelectric polarization and
magnetization), we further demonstrate reconfigurable logic-in-memory
operations in a single device. Our findings highlight the potential of
multiferroics for controlling magnon information transport and offer a pathway
towards room-temperature voltage-controlled, low-power, scalable magnonics for
in-memory computing.",2309.14614v1
2023-09-24,Dense strontium hexaferrite-based permanent magnet composites assisted by cold sintering process,"The use of rare-earth-based permanent magnets is one of the critical points
for the development of the current technology. On the one hand, industry of the
rare-earths is highly polluting due to the negative environmental impact of
their extraction and, on the other hand, the sector is potentially dependent on
China. Therefore, investigation is required both in the development of
rare-earth-free permanent magnets and in sintering processes that enable their
greener fabrication with attractive magnetic properties at a more competitive
price. This work presents the use of a cold sintering process (CSP) followed by
a post-annealing at 1100 {\deg}C as a new way to sinter composite permanent
magnets based on strontium ferrite (SFO). Composites that incorporate a
percentage < 10% of an additional magnetic phase have been prepared and the
morphological, structural and magnetic properties have been evaluated after
each stage of the process. CSP induces a phase transformation of SFO in the
composites, which is partially recovered by the post-thermal treatment
improving the relative density to 92% and the magnetic response of the final
magnets with a coercivity of up to 3.0 kOe. Control of the magnetic properties
is possible through the composition and the grain size in the sintered magnets.
These attractive results show the potential of the sintering approach as an
alternative to develop modern rare-earth-free composite permanent magnets.",2309.16038v1
2023-10-13,Optimizing site-specific specimen preparation for Atom Probe Tomography by using hydrogen for visualizing radiation-induced damage,"Atom probe tomography (APT) is extensively used to measure the local
chemistry of materials. Site-specific preparation via a focused ion beam (FIB)
is routinely implemented to fabricate needle-shaped specimens with an end
radius in the range of 50 nm. This preparation route is sometimes supplemented
by transmission Kikuchi diffraction (TKD) to facilitate the positioning of a
region of interest sufficiently close to the apex. Irradiating the specimen
with energetic electrons and ions can lead to the generation of vacancies and
even amorphization of the specimen. These extrinsically created vacancies
become crucial for probing the hydrogen or deuterium distribution since they
act as a strong trap. Here, we investigated the feasibility of site-specific
preparation of a two-phase medium-Mn steel containing austenite (fcc) and
ferrite (bcc). Following gaseous charging of APT specimens in deuterium (D2),
clusters enriched by up to 35 at.% D, are imaged after Pt deposition,
conventional Ga-FIB preparation, and TKD conducted separately. These D-rich
clusters are assumed to arise from the agglomeration of vacancies acting as
strong traps. By systematically eliminating these preparation-induced damages,
we finally introduce a workflow allowing for studying intrinsic traps for H/D
inherent to the material.",2310.09120v1
2023-12-25,Superplasticity-like behavior of ultrafine-grained austenitic steel 321,"Hot rolled commercial metastable austenitic steel 321 with strongly elongated
thin delta-ferrite particles in its microstructure was the object of
investigations. Ultrafine-grained (UFG) microstructure in steel 321 was formed
by Equal Channel Angular Pressing (ECAP) at 150 oC and 450 oC. When heating the
UFG steel specimens, the nucleation of sigma-phase particles blocking the grain
boundary migration was observed. The maximum elongation to failure (~250%) was
achieved at the deformation temperature 750 oC. The process of superplastic
deformation of the UFG steel 321 is controlled by simultaneous grain boundary
sliding and power-law creep. The contribution of each process depends on the
grain growth rate in the superplasticity regime as well as on defect
accumulation on the grain boundaries. The fracture of the UFG steel 321
specimens has a cavitational character - an intensive formation of large
elongated pores at the non-metallic particles as well as of the submicron pores
at the sigma-phase particles in the course of superplastic deformation were
observed.",2312.15785v1
2024-01-02,"Automated Segmentation of Large Image Datasets using Artificial Intelligence for Microstructure Characterisation, Damage Analysis and High-Throughput Modelling Input","Many properties of commonly used materials are driven by their
microstructure, which can be influenced by the composition and manufacturing
processes. To optimise future materials, understanding the microstructure is
critically important. Here, we present two novel approaches based on artificial
intelligence that allow the segmentation of the phases of a microstructure for
which simple numerical approaches, such as thresholding, are not applicable:
One is based on the nnU-Net neural network, and the other on generative
adversarial networks (GAN). Using large panoramic scanning electron microscopy
images of dual-phase steels as a case study, we demonstrate how both methods
effectively segment intricate microstructural details, including martensite,
ferrite, and damage sites, for subsequent analysis. Either method shows
substantial generalizability across a range of image sizes and conditions,
including heat-treated microstructures with different phase configurations. The
nnU-Net excels in mapping large image areas. Conversely, the GAN-based method
performs reliably on smaller images, providing greater step-by-step control and
flexibility over the segmentation process. This study highlights the benefits
of segmented microstructural data for various purposes, such as calculating
phase fractions, modelling material behaviour through finite element
simulation, and conducting geometrical analyses of damage sites and the local
properties of their surrounding microstructure.",2401.01147v3
2024-01-26,Engineering strong magnetoelectricity using a hexagonal 2D material on electron-doped hexagonal LuFeO$_3$,"Cubic perovskite-structure ABO$_3$ and A$_{1-x}$A$^{\prime}$$_x$BO$_3$-type
oxides have been investigated extensively while their hexagonal-structure
versions have received minimal attention, even though they are multiferroic and
can form heterostructures with the manifold hexagonal two-dimensional
materials. Hexagonal ferrites of the form RFeO$_3$, where R is yttrium or a
rare-earth element such as Lu, Yb, etc., feature coupled ferroelectricity (FE)
and weak-ferromagnetism (wFM), exhibiting linear magnetoelectricity. Their only
drawback is weak ferromagnetism. In this paper, we employ
density-functional-theory (DFT) calculations on hexagonal LuFeO$_3$ ($h$-LFO),
targeting its magnetic ordering by electron doping,anticipating
spin-disproportionation of the Fe sublattices. Indeed, we show that
spin-disproportionation in heavily-electron-doped versions
Lu$_{1-x}$Hf$_x$FeO$_3$ ($h$-LHFO), especially for x=1/3 and 1/2, leads to
robust out-of-plane collinear ferrimagnetism that is stable at room
temperature. Furthermore, the robust ferroelectricity of $h$-LFO persists via a
Jahn-Teller metal-to-insulator transition. Finally, we construct a
$h$-LHFO/$h$-2D heterostructure, where $h$-2D stands for the FE/FM monolayer
MnSTe, and demonstrate strong magnetoelectric coupling, namely manipulation of
magnetic skyrmions in MnSTe by an external electric field through the $h$-LHFO
polarization, opening up a new realm for magnetoelectric applications.",2401.15053v1
2010-08-18,Contraction and expansion effects on the substitution-defect properties of thirteen alloying elements in bcc Fe,"Proposed as blanket structural materials for fusion power reactors, reduced
activation ferritic/martensitic (RAFM) steel undergoes volume expanding and
contracting in a cyclic mode under service environment. Particularly, being
subjected to significant fluxes of fusion neutrons RAFM steel suffers
considerable local volume variations in the radiation damage involved regions.
It is necessary to study the structure properties of the alloying elements in
contraction and expansion states. In this paper we studied local substitution
structures of thirteen alloying elements Al, Co, Cr, Cu, Mn, Mo, Nb, Ni, Si,
Ta, Ti, V, and W in bcc Fe and calculated their substitutional energies in the
volume variation range from -1.0% to 1.0%. From the structure relaxation
results of the first five neighbor shells around the substitutional atom we
find the relaxation in each neighbor shell keeps approximately uniform within
the volume variation from -1.0% to 1.0% except those of Mn and the relaxation
of the fifth neighbor shell is stronger than that of the third and forth,
indicating that the lattice distortion due to the substitution atom is easier
to spread in <111> direction than in other direction. The relaxation pattern
and intensity are related to the size and electron structure of the
substitutional atom. For some alloying elements, such as Mo, Nb, Ni, Ta, Ti and
W, the substitutional energy decreases noticeably when the volume increases.
Further analysis show that the substitutional energy comprises the energy
variation originated from local structure relaxation and the chemical potential
difference of the substitutional atom between its elemental crystalline state
and the solid solution phase in bcc Fe. We think the approximately uniform
relaxation of each neighbor shell around a substitutional atom give rise to a
linear decrease in the substitutional energy with the increasing volume.",1008.3001v1
2014-07-30,Transition metal solute interactions with point defects in austenitic iron from first principles,"We present a comprehensive set of first principles electronic structure
calculations to study transition metal solutes and their interactions with
point defects in austenite. Clear trends were observed across the series.
Solute-defect interactions were strongly correlated to the solute size factors,
consistent with local strain field effects. Strong correlations with results in
ferrite show insensitivity to the underlying crystal structure in Fe. Oversized
solutes act as strong traps for vacancy and self-interstitial defects and as
nucleation sites for the development of proto-voids and small self-interstitial
loops. The reduction in defect mobility and net defect concentrations explains
the observed radiation-damage resistance in austenitic steels doped with
oversized solutes. Oversized solutes remaining dissolved in oxide
dispersion-strengthened (ODS) steels could contribute to their radiation-damage
resistance. Ni and Co diffuse more slowly than Fe, along with any vacancy flux
produced under irradiation below a critical temperature, which is 400 K for Co
and their concentrations should be enhanced at defect sinks. Cr and Cu diffuse
more quickly than Fe, against a vacancy flux and will be depleted at defect
sinks. Oversized solutes early in the transition metal series form
highly-stable solute-centred divacancy (SCD) defects with a nearest-neighbour
vacancy. The vacancy-mediated diffusion of these solutes is dominated by the
dissociation and reassociation of the SCDs, with a lower activation energy than
for self-diffusion, which has important implications for the nucleation and
growth of complex oxide nanoparticles containing these solutes in ODS steels.
Interstitial-mediated solute diffusion is energetically disfavoured for all
except Cr, Mn, Co and Ni. The central role that solute size plays in the
results presented here means they should apply to other solvent metals and
alloys.",1407.7996v1
2015-09-30,Roadmap for Emerging Materials for Spintronic Device Applications,"The Technical Committee of the IEEE Magnetics Society has selected 7 research
topics to develop their roadmaps, where major developments should be listed
alongside expected timelines; (i) hard disk drives, (ii) magnetic random access
memories, (iii) domain-wall devices, (iv) permanent magnets, (v) sensors and
actuators, (vi) magnetic materials and (vii) organic devices. Among them,
magnetic materials for spintronic devices have been surveyed as the first
exercise. In this roadmap exercise, we have targeted magnetic tunnel and
spin-valve junctions as spintronic devices. These can be used for example as a
cell for a magnetic random access memory and spin-torque oscillator in their
vertical form as well as a spin transistor and a spin Hall device in their
lateral form. In these devices, the critical role of magnetic materials is to
inject spin-polarised electrons efficiently into a non-magnet. We have
accordingly identified 2 key properties to be achieved by developing new
magnetic materials for future spintronic devices: (1) Half-metallicity at room
temperature (RT); (2) Perpendicular anisotropy in nano-scale devices at RT. For
the first property, 5 major magnetic materials are selected for their
evaluation for future magnetic/spintronic device applications: Heusler alloys,
ferrites, rutiles, perovskites and dilute magnetic semiconductors. These alloys
have been reported or predicted to be half-metallic ferromagnets at RT. They
possess a bandgap at the Fermi level EF only for its minority spins, achieving
100% spin polarisation at EF. We have also evaluated L10-alloys and
D022-Mn-alloys for the development of a perpendicularly anisotropic ferromagnet
with large spin polarisation. We have listed several key milestones for each
material on their functionality improvements, property achievements, device
implementations and interdisciplinary applications within 35 years time scale.",1509.08997v1
2019-05-10,Experimental Implementations of Cavity-Magnon Systems: from Ultra Strong Coupling to Applications in Precision Measurement,"Several experimental implementations of cavity-magnon systems are presented.
First an Yttrium Iron Garnet (YIG) block is placed inside a re-entrant cavity
where the resulting hybrid mode is measured to be in the ultra strong coupling
regime. When fully hybridised the ratio between the coupling rate and uncoupled
mode frequencies is determined to be $g/\omega=0.46$. Next a thin YIG cylinder
is placed inside a loop gap cavity. The bright mode of this cavity couples to
the YIG sample and is similarly measured to be in the ultra strong coupling
regime with ratio of coupling rate to uncoupled mode frequencies as
$g/\omega=0.34$. A larger spin density medium such as lithium ferrite (LiFe) is
expected to improve couplings by a factor of 1.46 in both systems as coupling
strength is shown to be proportional to the square root of spin density and
magnetic moment. Such strongly coupled systems are potentially useful for
cavity QED, hybrid quantum systems and precision dark matter detection
experiments. The YIG disc in the loop gap cavity, is, in particular, shown to
be a strong candidate for dark matter detection. Finally, a LiFe sphere inside
a two post re-entrant cavity is considered. In past work it was shown that the
magnon mode in the sample has a turnover point in frequency. Additionally, it
was predicted that if the system was engineered such that it fully hybridised
at this turnover point the cavity-magnon polariton (CMP) transition frequency
would become insensitive to both first and second order magnetic bias field
fluctuations, a result useful for precision frequency applications. This work
implements such a system by engineering the cavity mode frequency to near this
turnover point, with suppression in sensitivity to second order bias magnetic
field fluctuations shown.",1905.04002v2
2020-07-21,Atom probe characterisation of segregation driven Cu and Mn-Ni-Si co-precipitation in neutron irradiated T91 tempered-martensitic steel,"The T91 grade and similar 9Cr tempered-martensitic steels (also known as
ferritic-martensitic) are leading candidate structural alloys for fast fission
nuclear and fusion power reactors. At low temperatures (300 to 400 $^\circ$C)
neutron irradiation hardens and embrittles these steels, therefore it is
important to investigate the origin of this mode of life limiting property
degradation. T91 steel specimens were separately neutron irradiated to 2.14 dpa
at 327 $^\circ$C and 8.82 dpa at 377 $^\circ$C in the Idaho National Laboratory
Advanced Test Reactor. Atom probe tomography was used to investigate the
segregation driven formation of Mn-Ni-Si-rich (MNSPs) and Cu-rich (CRP)
co-precipitates. The precipitates increase in size and, slightly, in volume
fraction at the higher irradiation temperature and dose, while their
corresponding compositions were very similar, falling near the Si(Mn,Ni) phase
field in the Mn-Ni-Si projection of the Fe-based quaternary phase diagram.
While the structure of the precipitates has not been characterized, this
composition range is distinctly different than that of the typically cited
G-phase. The precipitates are composed of CRP with MNSP appendages. Such
features are often observed in neutron irradiated reactor pressure vessel (RPV)
steels. However, the Si, Ni, Mn, P and Cu solutes concentrations are lower in
the T91 than in typical RPV steels. Thus, in T91 precipitation primarily takes
place in solute segregated regions of line and loop dislocations. These results
are consistent with the model for radiation induced segregation driven
precipitation of MNSPs proposed by Ke et al. Cr-rich alpha prime ($\alpha$')
phase formation was not observed.",2007.10710v1
2018-05-16,"Single Crystal Permanent Magnet: Extraordinary Magnetic Behavior in the ta, Cu and Fe Substituted CeCo5 System","To reduce material and processing costs of commercial permanent magnets and
to attempt to fill the empty niche of energy products, 10 - 20 MGOe, between
low-flux (ferrites, alnico) and high-flux (Nd2Fe14B- and SmCo5-type) magnets,
we report synthesis, structure, magnetic properties and modeling of Ta, Cu and
Fe substituted CeCo5. Using a self-flux technique, we grew single crystals of I
- Ce15.1Ta1.0Co74.4Cu9.5, II - Ce16.3Ta0.6Co68.9Cu14.2, III -
Ce15.7Ta0.6Co67.8Cu15.9, IV - Ce16.3Ta0.3Co61.7Cu21.7 and V -
Ce14.3Ta1.0Co62.0Fe12.3Cu10.4. X-ray diffraction analysis (XRD) showed that
these materials retain a CaCu5 substructure and incorporate small amounts of Ta
in the form of \dumb-bells"", filling the 2e crystallographic sites within the
1D hexagonal channel with the 1a Ce site, whereas Co, Cu and Fe are
statistically distributed among the 2c and 3g crystallographic sites. Scanning
electron microscopy, energy dispersive X-ray spectroscopy (SEM-EDS) and
scanning transmission electron microscopy (STEM) examinations provided strong
evidence of the single-phase nature of the as-grown crystals, even though they
readily exhibited significant magnetic coercivitie of ~1.6 - ~1.8 kOe caused by
Co-enriched, nano-sized, structural defects and faults that can serve as
pinning sites. Formation of the ""composite crystal"" during the heat treatment
creates a 3D array of extended defects within a primarily single grain single
crystal, which greatly improves its magnetic characteristics. Possible causes
of the formation of the ""composite crystal"" may be associated with Ta atoms
leaving matrix interstices at lower temperatures and/or matrix degradation
induced by decreased miscibility at lower temperatures. Fe strongly improves
both the Curie temperature and magnetization of the system resulting in
(BH)max:~13 MGOe at room temperature.",1805.06545v1
2016-12-28,57Fe Mössbauer study of unusual magnetic structure of multiferroic 3R-AgFeO2,"We report new results of a 57Fe M\""ossbauer study of multiferroic 3R-AgFeO2
powder samples performed in a wide temperature range, including two points, TN1
~ 14 K and TN2 ~ 9 K, of magnetic phase transitions. At the intermediate
temperature range, TN2 < T < TN1, the 57Fe M\""ossbauer spectra can be described
in terms of collinear spin-density-waves (SDW) with the inclusion of many
high-order harmonics, indicating that the real magnetic structure of this
ferrite appears to be more complicated than a pure sinusoidally modulated SDW.
The spectra at low temperatures, T < TN2, consist of a Zeeman pattern with line
broadenings and sizeable spectral asymmetry. It has been shown that the
observed spectral shape is consistent with a transition to the elliptical
cycloidal magnetic structure. An analysis of the experimental spectra was
carried out under the assumption that the electric hyperfine interactions are
modulated when the Fe3+ magnetic moment rotates with respect to the principal
axis of the EFG tensor and emergence of the strong anisotropy of the magnetic
hyperfine field Hhf at the 57Fe nuclei. The large and temperature-independent
anharmonicity parameter, m ~ 0.78, of the cycloidal spin structure obtained
from the experimental spectra results from easy-axis anisotropy in the plane of
rotation of the iron spin. Analysis of different mechanisms of spin and
hyperfine interactions in 3R-AgFeO2 and its structural analogue CuFeO2 points
to a specific role played by the topology of the exchange coupling and the
oxygen polarization in the delafossite structures.",1612.08926v4
2019-10-11,"Low-Damping Ferromagnetic Resonance in Electron-Beam Patterned, High-$Q$ Vanadium Tetracyanoethylene Magnon Cavities","Integrating patterned, low-loss magnetic materials into microwave devices and
circuits presents many challenges due to the specific conditions that are
required to grow ferrite materials, driving the need for flip-chip and other
indirect fabrication techniques. The low-loss ($\alpha = 3.98 \pm 0.22 \times
10^{-5}$), room-temperature ferrimagnetic coordination compound vanadium
tetracyanoethylene ($\mathrm{V[TCNE]}_x$) is a promising new material for these
applications that is potentially compatible with semiconductor processing. Here
we present the deposition, patterning, and characterization of
$\mathrm{V[TCNE]}_x$ thin films with lateral dimensions ranging from 1 micron
to several millimeters. We employ electron-beam lithography and liftoff using
an aluminum encapsulated poly(methyl methacrylate), poly(methyl
methacrylate-methacrylic acid) copolymer bilayer (PMMA/P(MMA-MAA)) on sapphire
and silicon. This process can be trivially extended to other common
semiconductor substrates. Films patterned via this method maintain low-loss
characteristics down to 25 microns with only a factor of 2 increase down to 5
microns. A rich structure of thickness and radially confined spin-wave modes
reveals the quality of the patterned films. Further fitting, simulation, and
analytic analysis provides an exchange stiffness, $A_{ex} = 2.2 \pm 0.5 \times
10^{-10}$ erg/cm, as well as insights into the mode character and surface spin
pinning. Below a micron, the deposition is non-conformal, which leads to
interesting and potentially useful changes in morphology. This work establishes
the versatility of $\mathrm{V[TCNE]}_x$ for applications requiring highly
coherent magnetic excitations ranging from microwave communication to quantum
information.",1910.05325v1
2019-03-21,Quantitative magneto-optical imaging with ferrite garnets,"Magneto-optical imaging is a powerful technique for studying qualitative
features of magnetic flux distributions in superconductors and other magnetic
samples. However, magneto-optical imaging does not automatically return
two-dimensional maps with the actual values of the magnetic field, due to the
non-linear response functions of magneto-optical indicator films and in
practice also non-uniform illumination. A quantitative treatment is needed in
order to achieve such a calibration. After calibration, one can proceed to
deduce the corresponding two-dimensional maps of the current density
distribution from inversion of the Biot-Savart law. While there has been
published a large amount of work on quantitative magneto-optical imaging, the
material is scattered and notation differs significantly between different
authors. These notes originate from parts of the Ph. D. thesis of the author
and collect the most important materials into a unified and updated treatment.
Basic aspects of magnetic flux penetration in superconductors including the
Bean model are reviewed briefly in chapter 1. In chapter 2, the method of
magneto-optical imaging using the Faraday effect is introduced, together with
practical aspects of magneto-optical experiments at low temperatures and the
semi-qualitative technique of RGB addition for checking the reproducibility of
flux patterns. The physics of magneto-optical indicator films and calibration
of magneto-optical images into maps of magnetic field values are discussed in
chapter 3. Next, in chapter 4 the Biot-Savart law and fast Fourier
transformations are discussed before proceeding to inversion of magnetic field
maps into current density maps. Finally, magnetometry with Faraday
magneto-optical imaging is treated. MATLAB codes for several of the discussed
concepts can be found at https://github.com/atlejq/Magneto-optics",1903.09130v1
2020-06-25,"Influence of Yb3+on the structural, electrical and optical properties of sol-gel synthesized Ni-Zn nanoferrites","Polycrystalline Yb substituted NiZn nanoferrites with the compositions of
Ni0.5Zn0.5YbxFe2-xO4 (x= 0.00, 0.04, 0.08, 0.12, 0.16 and 0.20) have been
synthesized using sol gel auto combustion technique. Single phase cubic spinel
structure has been confirmed by the X ray diffraction (XRD) patterns. Larger
lattice constants of the compositions are found with increasing Yb3+
concentration while the average grain size (52 to 18 nm) has noticeable
decrease as Yb3+ content is increased. The presence of all existing elements as
well as the purity of the samples has also been confirmed from energy
dispersive X ray spectroscopic (EDS) analysis. Frequency dependent dielectric
constant, dielectric loss, dielectric relaxation time, AC and DC resistivity of
the compositions have also been examined at room temperature. The DC
resistivity value is found in the order of 10 to power 10 (omega-cm) which is
at least four orders greater than the ferrites prepared by conventional method.
This larger value of resistivity attributes due to very small grain size and
successfully explained using the Verwey and deBoer hopping conduction model.
The contribution of grain and grain boundary resistance has been elucidated
using Cole Cole plot. The study of temperature dependent DC resistivity
confirms the semiconducting nature of all titled compositions wherein bandgap
(optical) increases from 2.73 eV to 3.25 eV with the increase of Yb content.
The high value of resistivity is of notable achievement for the compositions
that make them a potential candidate for implication in the high frequency
applications where reduction of eddy current loss is highly required.",2006.14180v1
2021-09-06,Critical State Theory For The Magnetic Coupling Between Soft Ferromagnetic Materials And Type-II Superconductors,"Improving our understanding of the physical coupling between type-II
superconductors (SC) and soft ferromagnetic materials (SFM), is root for
progressing onto the application of SC-SFM metastructures in scenarios such as
magnetic cloaking, magnetic shielding, and power transmission systems. However,
in the latter some intriguing and yet unexplained phenomena occurred, such as a
noticeable rise in the SC energy losses, and a local but not isotropic
deformation of its magnetic flux density. These phenomena, which are in
apparent contradiction with the most fundamental theory of electromagnetism for
superconductivity, i.e., the critical state theory (CST), have remained
unexplained for about 20 years, given place to the acceptance of the
controversial and yet paradigmatic existence of the so-called overcritical
current densities. Therefore, aimed to resolve these long-standing problems, we
extended the CST by incorporating a semi-analytical model for cylindrical
monocore SC-SFM heterostructures, setting the standards for its validation with
a variational approach of multipole functionals for the magnetic coupling
between Sc and SFM materials. It is accompanied by a comprehensive numerical
study for SFM sheaths of arbitrary dimensions and magnetic relative
permeabilities $\mu_{r}$, ranging from $\mu_{r}=5$ (NiZn ferrites) to
$\mu_{r}=350000$ (pure Iron), showing how the AC-losses of the SC-SFM
metastructure radically changes as a function of the SC and the SFM radius for
$\mu_{r} \geq 100$. Our numerical technique and simulations revealed also a
good qualitative agreement with the magneto optical imaging observations that
were questioning the CST validness, proving therefore that the reported
phenomena for self-field SC-SFM heterostructures can be understood without
including the ansatz of overcritical currents.",2109.02604v2
2021-11-12,"Implementing and evaluating far-field 3D X-ray diffraction at the I12 JEEP beamline, Diamond Light Source","Three-dimensional X-ray diffraction (3DXRD) is shown to be feasible at the
I12 Joint Engineering, Environmental and Processing (JEEP) beamline of Diamond
Light Source. As a demonstration, a microstructually simple low-carbon ferritic
steel was studied in a highly textured and annealed state. A processing
pipeline suited to this beamline was created, using software already
established in the 3DXRD user community, enabling grain centre-of-mass
positions, orientations and strain tensor elements to be determined.
Orientations, with texture measurements independently validated from electron
backscatter diffraction (EBSD) data, possessed a $\sim 0.1^\circ$ uncertainty,
comparable with other 3DXRD instruments. The spatial resolution was limited by
the far-field detector pixel size; the average of the grain centre of mass
position errors was determined as $\pm \sim 80 \mu$m. An average per-grain
error of $\sim 1 \times 10^{-3}$ for the elastic strains was also measured;
this could be reduced in future experiments by improving sample preparation,
data collection and analysis techniques. Application of 3DXRD onto I12 shows
great potential, where its implementation is highly desirable due the flexible,
open architecture of the beamline. User-owned or designed sample environments
can be used, thus 3DXRD could be applied to previously unexplored scientific
areas.",2111.06779v2
2022-11-17,On the critical role of martensite hardening behavior in the paradox of local and global ductility in dual-phase steels,"Experimental findings in the literature reveal that DP steels with identical
strength and composition, but different microstructures, exhibit inconsistent
trends under either necking-controlled or damage-controlled ductility tests. A
special case of this phenomenon is referred to in the forming community as the
cut-edge failure or edge cracking issue of DP steels. It is observed that
globally ductile microstructures are prone to premature damage at cut edges
while a comparatively less ductile DP steel performs better under the locally
applied deformation at such edges. In this paper, a systematical statistical
study is conducted to analyse this paradox from a micromechanical point of
view. The obtained results qualitatively confirm the experimental observations
and allowed us to explain/rationalize them, as follows. To reach a higher
necking-controlled ductility, i.e. global ductility, the mechanical contrast
between ferrite and martensite must be increased. Since martensite reveals a
very high initial hardening and fast saturation, activation of martensite
plasticity will lead to early necking in the microstructure and should
therefore be avoided; a high mechanical phase contrast has this effect.
However, at the same time a higher mechanical phase contrast is detrimental for
the local ductility. More heterogeneity in the microstructure causes the
generation of higher local plastic strains and triaxial stresses which leads to
early damages. Therefore, in DP steel, increasing the global ductility may come
at the expense of decreasing local ductility, and vice versa. The martensite
hardening behavior is the main factor governing this phenomenon, and therefore
also constitutes the key to processing improved steels that combine the best of
both.",2211.09720v1
2023-02-24,Nuclear quadrupole resonance spectroscopy with a femtotesla diamond magnetometer,"Sensitive Radio-Frequency (RF) magnetometers that can detect oscillating
magnetic fields at the femtotesla level are needed for demanding applications
such as Nuclear Quadrupole Resonance (NQR) spectroscopy. RF magnetometers based
on Nitrogen-Vacancy (NV) centers in diamond have been predicted to offer
femtotesla sensitivity, but published experiments have largely been limited to
the picotesla level. Here, we demonstrate a femtotesla RF magnetometer based on
an NV-doped diamond membrane inserted between two ferrite flux concentrators.
The device operates in bias magnetic fields of 2-10 microtesla and provides a
~300-fold amplitude enhancement within the diamond for RF magnetic fields in
the 0.07-3.6 MHz range. The magnetometer's sensitivity is ~70 fT s^{1/2} at
0.35 MHz, and the noise floor decreases to below 2 fT after 1 hour of
acquisition. We used this sensor to detect the 3.6 MHz NQR signal of 14N in
sodium nitrite powder at room temperature. NQR signals are amplified by a
resonant RF coil wrapped around the sample, allowing for higher signal-to-noise
ratio detection. The diamond RF magnetometer's recovery time after a strong RF
pulse is ~35 us, limited by the coil ring-down time. The sodium-nitrite NQR
frequency shifts linearly with temperature as -1.00 +/- 0.02 kHz/K, the
magnetization dephasing time is T2* = 887 +/- 51 us, and a spin-lock spin-echo
pulse sequence extends the signal lifetime to 332 +/- 23 ms, all consistent
with coil-based NQR studies. Our results expand the sensitivity frontier of
diamond magnetometers to the femtotesla range, with potential applications in
security, medical imaging, and materials science.",2302.12401v1
2023-04-05,A Checklist to Publish Collections as Data in GLAM Institutions,"Large-scale digitization in Galleries, Libraries, Archives and Museums (GLAM)
created the conditions for providing access to collections as data. It opened
new opportunities to explore, use and reuse digital collections. Strong
proponents of collections as data are the Innovation Labs which provided
numerous examples of publishing datasets under open licenses in order to reuse
digital content in novel and creative ways. Within the current transition to
the emerging data spaces, clouds for cultural heritage and open science, the
need to identify practices which support more GLAM institutions to offer
datasets becomes a priority, especially within the smaller and medium-sized
institutions.
  This paper answers the need to support GLAM institutions in facilitating the
transition into publishing their digital content and to introduce collections
as data services; this will also help their future efficient contribution to
data spaces and cultural heritage clouds. It offers a checklist that can be
used for both creating and evaluating digital collections suitable for
computational use. The main contributions of this paper are i) a methodology
for devising a checklist to create and assess digital collections for
computational use; ii) a checklist to create and assess digital collections
suitable for use with computational methods; iii) the assessment of the
checklist against the practice of institutions innovating in the Collections as
data field; and iv) the results obtained after the application and
recommendations for the use of the checklist in GLAM institutions.",2304.02603v2
2023-06-13,"Noise and Thermal Performance of a Sub-Attofarad Capacitance Sensor for Precision Measurements, with Applications in Gravitational Wave Detectors","We describe the design principles, fabrication, and characterization of a
precision AC resonant capacitance bridge (RCB) sensor, based on a resonant
differential planar printed circuit board transformer with a solid (ungapped)
MnZn ferrite core, demonstrating a short-term sensitivity at 293 K of 0.225 +/-
0.005 aF/rtHz, at around 120 kHz resonance frequency and 1 Hz Fourier
measurement frequency. At 120 K the RCB short term noise sensitivity is 0.118
+/- 0.005 aF/rtHz. We compare the ungapped configuration to five different
RCBs; three with a core gap of 65 um and two with a core gap of 130 um. Their
average room temperature short term noise sensitivities are 0.30 +/- 0.01
aF/rtHz and 0.45 +/- 0.01 aF/rtHz, while the cryogenic operation of these
transformers at 120 K resulted in averaged sensitivities of 0.23 +/- 0.01
aF/rtHz and of 0.36 +/- 0.01 aF/rtHz respectively. Multi-hour room temperature
runs, with one core of each of the three gap types, proved the stability of
their long-term sensitivities of 0.234 +/- 0.005 aF/rtHz, 0.338 +/- 0.009
aF/rtHz, and 0.435 +/- 0.010 aF/rtHz for the ungapped (40-hour duration) and
the 65 um and 130 um (28-hour duration) cores respectively. At 0.1 mHz, a
critical frequency for space gravitational wave detectors, the respective
sensitivities are 0.25 +/- 0.02 aF/rtHz, 0.35 +/- 0.02 aF/rtHz, and 0.53 +/-
0.07 aF/rtHz. Measurements with the ungapped transformer configuration for
temperatures from 325 K to 349 K further validate the dependence of the noise
model on the temperature and permeability. The performance of our RCB with an
ungapped core matches the calculated performance value and shows an improvement
in signal-to-noise of two or more compared with capacitance bridges developed
for similar applications. A further factor of about two noise reduction is
achieved by cooling to 120 K.",2306.08124v3
2023-08-25,High-susceptibility nanoparticles for micro-inductor core materials,"According to the laws of magnetism, the shape of magnetically soft objects
limits the effective susceptibility. For example, spherical soft magnets cannot
display an effective susceptibility larger than 3. Although true for
macroscopic multi-domain magnetic materials, we show that magnetic
nanoparticles in a single-domain state do not suffer from this limitation. This
is a consequence of the particle moment being forced to saturation by the
predominance of exchange forces, and only allowed to rotate coherently in
response to thermal and/or applied fields. We apply statistical mechanics to
determine the static and dynamic susceptibility of single-domain particles as a
function of size, temperature and material parameters. Our calculations reveal
that spherical single-domain particles with large saturation magnetisation and
small magneto-crystalline anisotropy, e.g. FeNi particles, can have very a
large susceptibility of 200 or more. We further show that susceptibility and
losses can be tuned by particle easy axis alignment with the applied field in
case of uniaxial anisotropy, but not for particles with cubic anisotropy. Our
model is validated experimentally by comparison with measurements on
nanocomposites containing spherical 11$\pm$3 nm $\gamma$-Fe$_2$O$_3$ particles
up to 45 vol% finely dispersed in a polymer matrix. In agreement with the
calculations for this specific material, the measured susceptibility of the
composites is up to 17 ($\gg$3) and depends linearly on the volume fraction of
particles. Based on these results, we predict that nanocomposites of 30 vol% of
superparamagnetic FeNi particles in an insulating non-magnetic matrix can have
a sufficiently large susceptibility to be used as micro-inductor core materials
in the MHz frequency range, while maintaining losses below state-of-the-art
ferrites.",2308.13407v2
2023-09-16,Temperature-Induced Hexagonal-Orthorhombic Phase Transition in Lutetium Ferrite Nanoparticles,"The X-ray diffraction, Raman and infrared spectroscopies and magnetic
measurements were used to explore the correlated changes of the structure,
lattice dynamics and magnetic properties of the LuFeO3 nanoparticles, which
appear in dependence on their sintering temperature. We revealed a gradual
substitution of the hexagonal phase by the orthorhombic phase in the
nanoparticles, which sintering temperature increases from 700 C to 1100 C. The
origin and stability of the hexagonal phase in the LuFeO3 nanoparticles is of
the special interest, because the nanoparticle in the phase can be a
room-temperature multiferroic with a weak ferromagnetic and pronounced
structural and ferroelectric long-range ordering, while the antiferromagnetic
and nonpolar orthorhombic phase is more stable in the bulk LuFeO3. To define
the ranges of the hexagonal phase stability, we determine the bulk and
interface energy densities of different phases from the comparison of the Gibbs
model with experimental results. Using the Gibbs model parameters, we predict
the influence of size effects and temperature on the structural and polar
properties of the LuFeO3 nanoparticles. Analysis of the obtained results shows
that the combination of the X-ray diffraction, Raman and infrared spectroscopy,
magnetic measurements and theoretical modelling of structural and polar
properties allows to establish the interplay between the phase composition,
lattice dynamics and multiferroic properties of the LuFeO3 nanoparticles
prepared in different conditions.",2309.09109v5
2023-09-24,In-depth investigations of size and occupancies in cobalt ferrite nanoparticles by joint Rietveld refinements of X-ray and neutron powder diffraction data,"Powder X-ray diffraction (PXRD) and neutron powder diffraction (NPD) have
been used to investigate the crystal structure of CoFe2O4 nanoparticles
prepared via different hydrothermal synthesis routes, with particular attention
given to accurately determining the spinel inversion degrees. The study is
divided into four parts. In the first part, the investigations focus on the
influence of using different diffraction pattern combinations (NPD, Cu-source
PXRD and Co-source PXRD) for the structural modelling. It is found that
combining PXRD data from a Co source with NPD data offers a robust structural
model. The second part of the study evaluates the reproducibility of the
employed multipattern Rietveld refinement procedure using different data sets
collected on the same sample, as well as on equivalently prepared samples. The
refinement procedure gives reproducible results and reveals that the synthesis
method is likewise reproducible since only minor differences are noted between
the samples. The third part focuses on the structural consequences of (i) the
employed heating rate (achieved using three different hydrothermal reactor
types) and (ii) changing the cobalt salt in the precursors [aqueous salt
solutions of Co(CH3COOH)2, Co(NO3)2 and CoCl2] in the synthesis. It is found
that increasing the heating rate causes a change in the crystal structure (unit
cell and crystallite sizes) while the Co/Fe occupancy and magnetic parameters
remain similar in all cases. Also, changing the type of cobalt salt does not
alter the final crystal/magnetic structure of the CoFe2O4 nanoparticles. The
last part of this study is a consideration of the chemicals and parameters used
in the synthesis of the different samples.",2309.16037v1
2023-11-06,Grain-level effects on in-situ deformation-induced phase transformations in a complex-phase steel using 3DXRD and EBSD,"A novel complex-phase steel alloy is conceived with a deliberately unstable
austenite, $\gamma$, phase that enables the deformation-induced martensitic
transformations (DIMT) to be explored at low levels of plastic strain. The DIMT
was thus explored, in-situ and non-destructively, using both far-field
Three-Dimensional X-Ray Diffraction (3DXRD) and Electron Back-Scatter
Diffraction (EBSD). Substantial $\alpha'$ martensite formation was observed
under 10% applied strain with EBSD, and many $\varepsilon$ grain formation
events were captured with 3DXRD, indicative of the indirect transformation of
martensite via the reaction $\gamma \rightarrow \varepsilon \rightarrow
\alpha'$. Using $\varepsilon$ grain formation as a direct measurement of
$\gamma$ grain stability, the influence of several microstructural properties,
such as grain size, orientation and neighbourhood configuration, on $\gamma$
stability have been identified. Larger $\gamma$ grains were found to be less
stable than smaller grains. Any $\gamma$ grains oriented with {100} parallel to
the loading direction preferentially transformed with lower stresses. Parent
$\varepsilon$-forming $\gamma$ grains possessed a neighbourhood with increased
ferritic/martensitic volume fraction. This finding shows, unambiguously, that
$\alpha$/$\alpha'$ promotes $\varepsilon$ formation in neighbouring grains. The
minimum strain work criterion model for $\varepsilon$ variant prediction was
also evaluated, which worked well for most grains. However,
$\varepsilon$-forming grains with a lower stress were less well predicted by
the model, indicating crystal-level behaviour must be considered for accurate
$\varepsilon$ formation. The findings from this work are considered key for the
future design of alloys where the deformation response can be controlled by
tailoring microstructure and local or macroscopic crystal orientations.",2311.03088v2