publicationDate,title,abstract,id
2019-05-30,Sub-nanosecond switching in a cryogenic spin-torque spin-valve memory element with a dilute permalloy free layer,"We present a study of the pulsed current switching characteristics of
spin-valve nanopillars with in-plane magnetized dilute permalloy and undiluted
permalloy free layers in the ballistic regime at low temperature. The dilute
permalloy free layer device switches much faster: the characteristic switching
time for a permalloy free (Ni0.83Fe0.17) layer device is 1.18 ns, while that
for a dilute permalloy ([Ni0.83Fe0.17]0.6Cu0.4) free layer device is 0.475 ns.
A ballistic macrospin model can capture the data trends with a reduced spin
torque asymmetry parameter, reduced spin polarization and increased Gilbert
damping for the dilute permalloy free layer relative to the permalloy devices.
Our study demonstrates that reducing the magnetization of the free layer
increases the switching speed while greatly reducing the switching energy and
shows a promising route toward even lower power magnetic memory devices
compatible with superconducting electronics.",1905.13262v1
2011-12-11,Memory effects in permalloy-niobium hybrid structures,"The kineticts of magnetization reversal of stripe-shaped permalloy-niobium
hybrid nanofilms is studied in 6-300 K temperature range by means of
magneto-optics visualization technique. The niobium influence on magnetic
domain walls type and on magnetic domain structure of permalloy via the
interface quality and via the distortion of stray fields is found. The memory
effect, which is the superconducting niobium memory about an initial magnetic
domain structure of permalloy at cooling below T_c, is found. The memory is
razed only by hybrid heating over T_c.",1112.2359v1
2021-01-25,A solution to the permalloy problem,"We propose a solution to the longstanding permalloy problem$-$why the
particular composition of permalloy, Fe$_{21.5}$Ni$_{78.5}$, achieves a
dramatic drop in hysteresis, while its material constants show no obvious
signal of this behavior. We use our recently developed coercivity tool to show
that a delicate balance between local instabilities and magnetic material
constants are necessary to explain the dramatic drop of hysteresis at 78.5% Ni.
Our findings are in agreement with the permalloy experiments and, more broadly,
provide theoretical guidance for the discovery of novel low hysteresis magnetic
alloys.",2101.09857v1
2013-10-29,Influence of sample geometry on inductive damping measurement methods,"We study the precession frequency and effective damping of patterned
permalloy thin films of different geometry using integrated inductive test
structures. The test structures consist of coplanar wave guides fabricated onto
patterned permalloy stripes of different geometry. The width, length and
position of the permalloy stripe with respect to the center conductor of the
wave guide are varied. The precession frequency and effective damping of the
different devices is derived by inductive measurements in time and frequency
domain in in-plane magnetic fields. While the precession frequencies do not
reveal a significant dependence on the sample geometry we find a decrease of
the measured damping with increasing width of the permalloy centered underneath
the center conductor of the coplanar wave guide. We attribute this effect to an
additional damping contribution due to inhomogeneous line broadening at the
edges of the permalloy stripes which does not contribute to the inductive
signal provided the permalloy stripe is wider than the center conductor.
Consequences for inductive determination of the effective damping using such
integrated reference samples are discussed.",1310.7817v1
2018-05-30,Magnonic band gap and mode hybridization in continuous Permalloy film induced by vertical coupling with an array of Permalloy ellipses,"We investigate magnonic band structure in thin homogeneous permalloy film
decorated with periodic array of elliptically shaped permalloy dots and
separated by non-magnetic Pt spacer. We demonstrated experimentally formation
of the magnonic band structure for Damon-Eshbach wave propagating in permalloy
film with the band gap opened at the Brillouin zone border and band splitting
at smaller wavenumbers, due to the Bragg interference and interaction of
propagating wave of the continuous film with a standing resonant mode of the
nano-ellipses, respectively. The shape anisotropy of the permalloy nanodots
allows to control the spin wave dynamics through the switch between two states
of the magnetization with respect to the underneath film magnetization, thus
enabling magnonic band structure reprogrammability. With numerical analysis we
show, that predominant role in formation of the magnonic band structure is
played by a vertical dynamic coupling between propagating wave in the film and
magnetization oscillations in the nanodots.",1805.12178v2
2017-02-17,Magnetic anisotropy in Permalloy: hidden quantum mechanical features,"By means of relativistic, first principles calculations, we investigate the
microscopic origin of the vanishingly low magnetic anisotropy of Permalloy,
here proposed to be intrinsically related to the local symmetries of the alloy.
It is shown that the local magnetic anisotropy of individual atoms in Permalloy
can be several orders of magnitude larger than that of the bulk sample, and
5-10 times larger than that of elemental Fe or Ni. We, furthermore, show that
locally there are several easy axis directions that are favored, depending on
local composition. The results are discussed in the context of perturbation
theory, applying the relation between magnetic anisotropy and orbital moment.
Permalloy keeps its strong ferromagnetic nature due to the exchange energy to
be larger than the magnetocrystalline anisotropy. Our results shine light on
the magnetic anisotropy of permalloy and of magnetic materials in general, and
in addition enhance the understanding of pump-probe measurements and ultrafast
magnetization dynamics.",1702.05414v1
2023-11-10,Exchange stiffness proportional to power of magnetization in permalloy co-doped with Mo and Cu,"The exchange stiffness of magnetic materials is one of the essential
parameters governing magnetic texture and its dynamics in magnetic devices. The
effect of single-element doping on exchange stiffness has been investigated for
several doping elements for permalloy (NiFe alloy), a soft magnetic material
whose soft magnetic properties can be controlled by doping. However, the impact
of more practical multi-element doping on the exchange stiffness of permalloy
is unknown. This study investigates the typical magnetic properties, including
exchange stiffness, of permalloy systematically co-doped with Mo and Cu using
broadband ferromagnetic resonance spectroscopy. We find that the exchange
stiffness, which decreases with increasing doping levels, is proportional to a
power of magnetization, which also decreases with increasing doping levels. The
magnetization, $M_{\rm s}$, dependence of the exchange stiffness constant, $A$,
of all the investigated samples, irrespective of the doping levels of each
element, lies on a single curve expressed as $A\propto M_{\rm s}^n$ with
exponent $n$ close to 2. This empirical power-law relationship provides a
guideline for predicting unknown exchange stiffness in non-magnetic
element-doped permalloy systems.",2311.05852v2
2004-08-28,"Current-Induced Magnetization Switching in Permalloy-based Nanopillars with Cu, Ag, and Au","We compare magnetoresistances (MR) and switching currents (I_s) at room
temperature (295K) and 4.2K for Permalloy/N/Permalloy nanopillars undergoing
current-induced magnetization switching (CIMS), with non-magnetic metals N =
Cu, Ag, and Au. The N-metal thickness is held fixed at 10 nm. Any systematic
differences in MR and I_s for the different N-metals are modest, suggesting
that Ag and Au represent potentially viable alternatives for CIMS studies and
devices to the more widely used Cu.",0408632v1
2008-09-01,Quantum transport in ferromagnetic Permalloy nanostructures,"We studied phase coherent phenomena in mesoscopic Permalloy samples by
exploring low temperature transport. Both, differential conductance as a
function of bias voltage and magnetoconductance of individual wires display
conductance fluctuations. Analysis of these fluctuations yields a phase
coherence length of $\sim250$ nm at 25 mK as well as a $1/\sqrt{T}$ temperature
dependence. To suppress conductance fluctuations by ensemble averaging we
investigated low temperature transport in wire arrays and extended Permalloy
films. In these samples we have measured conductance corrections which stem
from electron-electron interaction (EEI) but attempts to detect signatures of
weak localization were without success.",0809.0192v1
2013-10-15,Transverse spin Seebeck vs. Anomalous and Planar Nernst Effects in Permalloy Thin Films,"Transverse magneto-thermoelectric effects are studied in permalloy thin films
grown on MgO and GaAs substrates and compared to those grown on suspended SiN
membranes. The transverse voltage along platinum strips patterned on top of the
permalloy films is measured vs. the external magnetic field as a function of
angle and temperature gradient. After the identification of the contribution of
the planar and anomalous Nernst effects, we find an upper limit for the
transverse spin Seebeck effect, which is several orders of magnitude smaller
than previously reported.",1310.4045v1
2016-12-21,Flexible Bacterial Cellulose Permalloy nanocomposite xerogel sheets size scalable magnetic actuator cum electrical conductor,"Permalloy nanoparticles containing bacterial cellulose hydrogel obtained
after reduction was compressed into a xerogel flexible sheet by hot pressing at
60 C at different pressures. The permalloy nanoparticles with an ordered
structure have a bimodal size distribution centered around 25 nm and 190 nm.
The smaller nanoparticles are superparamagnetic while the larger particles are
ferromagnetic at room temperature. The sheets have a room temperature
magnetisation of 20 emu/g and a coercivity of 32 Oe. The electrical
conductivity of the flexible sheets increases with hot pressing pressure from 7
S/cm to 40 S/cm at room temperature.",1701.02792v1
2019-04-03,Spin diffusion length of Permalloy using spin absorption in lateral spin valves,"We employ the spin absorption technique in lateral spin valves to extract the
spin diffusion length of Permalloy (Py) as a function of temperature and
resistivity. A linear dependence of the spin diffusion length with conductivity
of Py is observed, evidencing that Elliott-Yafet is the dominant spin
relaxation mechanism in Permalloy. Completing the data set with additional data
found in literature, we obtain $\lambda_{Py}= (0.91\pm 0.04) (f\Omega
m^2)/\rho_{Py}$.",1904.01921v1
2003-07-12,Nanoscale Zeeman localization of charge carriers in diluted magnetic semiconductor-permalloy hybrids,"We investigate the possibility of charge carrier localization in magnetic
semiconductors due to the presence of a highly inhomogeneous external magnetic
field. As an example, we study in detail the properties of a magnetic
semiconductor-permalloy disk hybrid system. We find that the giant Zeeman
respose of the magnetic semiconductor in conjuction with the highly non-uniform
magnetic field created by the vortex state of a permalloy disk can lead to
Zeeman localized states at the interface of the two materials. These trapped
state are chiral, with chirality controlled by the orientation of the core
magnetization of the permalloy disk. We calculate the energy spectrum and the
eigenstates of these Zeeman localized states, and discuss their experimental
signatures in spectroscopic probes.",0307305v1
2018-04-17,Reprogrammable magnonic band structure of layered Permalloy/Cu/Permalloy nanowires,"Reprogrammability of magnonic band structure in layered
Permalloy/Cu/Permalloy nanowires is demonstrated to depend on the relative
orientation of the two layers magnetization. By using Brillouin light
spectroscopy, we show that when the layers are aligned parallel two dispersive
modes, with positive and negative group velocity, are observed while when the
magnetic layers are aligned anti-parallel, only one dispersive mode, with
positive group velocity, is detected. Our findings are successfully compared
and interpreted in terms of a microscopic (Hamiltonian-based) method. An
explanation for the observed behavior can be attributed to mode-mixing (or
hybridization) effect when the two magnetic layers are aligned anti-parallel.
This work opens the path to magnetic field-controlled reconfigurable magnonic
crystals with multi-modal frequency transmission characteristics.",1804.06217v1
2019-09-10,Spin Pumping from Permalloy into Uncompensated Antiferromagnetic Co doped Zinc Oxide,"Heterostructures of Co-doped ZnO and Permalloy were investigated for their
static and dynamic magnetic interaction. The highly Co-doped ZnO is
paramagentic at room temperature and becomes an uncompensated antiferromagnet
at low temperatures, showing a narrowly opened hysteresis and a vertical
exchange bias shift even in the absence of any ferromagnetic layer. At low
temperatures in combination with Permalloy an exchange bias is found causing a
horizontal as well as vertical shift of the hysteresis of the heterostructure
together with an increase in coercive field. Furthermore, an increase in the
Gilbert damping parameter at room temperature was found by multifrequency FMR
evidencing spin pumping. Temperature dependent FMR shows a maximum in magnetic
damping close to the magnetic phase transition. These measurements also
evidence the exchange bias interaction of Permalloy and long-range ordered
Co-O-Co structures in ZnO, that are barely detectable by SQUID due to the
shorter probing times in FMR.",1909.04362v3
2021-06-21,Resonant Measurement of Non-Reorientable Spin-Orbit Torque from a Ferromagnetic Source Layer Accounting for Dynamic Spin Pumping,"Using a multilayer structure containing (cobalt detector layer)/(copper
spacer)/(Permalloy source layer), we show experimentally how the
non-reorientable spin-orbit torque generated by the Permalloy source layer (the
component of spin-orbit torque that does not change when the Permalloy
magnetization is rotated) can be measured using spin-torque ferromagnetic
resonance (ST-FMR) with lineshape analysis. We find that dynamic spin pumping
between the magnetic layers exerts torques on the magnetic layers as large or
larger than the spin-orbit torques, so that if dynamic spin pumping is
neglected the result would be a large overestimate of the spin-orbit torque.
Nevertheless, the two effects can be separated by performing ST-FMR as a
function of frequency. We measure a non-reorientable spin torque ratio
$\xi_{\text{Py}} = 0.04 \pm 0.01$ for spin current flow from Permalloy through
an 8 nm Cu spacer to the Co, and a strength of dynamic spin pumping that is
consistent with previous measurements by conventional ferromagnetic resonance.",2106.11127v1
2014-06-01,Diffusivities and kinetics of short-range and long-range orderings in Ni-Fe permalloys,"The microscopic model of atomic diffusion is considered to describe the
short-range order relaxation kinetics within the f.c.c.-Ni-Fe Permalloys. The
model takes into account both the discrete and anisotropic characters of atomic
jumps within the long-range field of concentration heterogeneities of the
interacting atoms. The diffusion coefficients and activation energies for the
disordered Ni-Fe permalloy are estimated with the evaluated probabilities of
atomic jumps. As shown, the increasing of a temperature with a fixed
composition influences on the 'potential' field of interatomic interaction
ambiguously: the field 'potential' increases for defined coordination shells
and decreases for some of other ones. Although the temperature increasing
promotes the increasing of any atomic-probabilities jumps generally, but
decreasing of the action of 'potential' field generated by the atoms of defined
element and caused by its concentration heterogeneities onto the distant sites
results in increasing of the atomic-jumps' probabilities of just this element,
first of all, into the sites, which are more distant from the 'source' of
heterogeneity. Within the framework of the static concentration waves' method
along with the self-consistent field approximation, the Onsager-type kinetics
equation is obtained to describe the long-range order relaxation by the
L12-type superstructure. To calculate diffusivities for the ordered Ni3Fe
permalloy, the independent, diffraction experimental data of the long-range
order parameter relaxation are used. Theoretical curves of the long-range order
time evolution for the non-stoichiometric f.c.c.-Ni-Fe permalloys are plotted.
Decreasing of the concentration of alloying element results in decelerating of
the long-range order parameter change and in increasing of its relaxation time.",1406.0147v1
2023-03-07,The Role of Self-Torques in Transition Metal Dichalcogenide/Ferromagnet Bilayers,"Recently, transition metal dichalcogenides (TMDs) have been extensively
studied for their efficient spin-orbit torque generation in TMD/ferromagnetic
bilayers, owing to their large spin-orbit coupling, variety in crystal
symmetries, and pristine interfaces. Although the TMD layer was considered
essential for the generation of the observed SOTs, recent reports show the
presence of a self-torque in single-layer ferromagnetic devices with magnitudes
comparable to TMD/ferromagnetic devices. Here, we perform second-harmonic Hall
SOT measurements on metal-organic chemical vapor deposition (MOCVD) grown
MoS$_{2}$/permalloy/Al$_{2}$O$_{3}$ devices and compare them to a single-layer
permalloy/Al$_{2}$O$_{3}$ device to accurately disentangle the role of
self-torques from contributions from the TMD layer. We report a damping-like
self-torque conductivity of opposite sign in our single-layer
permalloy/Al$_{2}$O$_{3}$ device compared to one
MoS$_{2}$/permalloy/Al$_{2}$O$_{3}$ device, and find no significant one for all
other MoS$_{2}$/permalloy/Al$_{2}$O$_{3}$ devices. This indicates a competition
between the self-torque and the torque arising from the TMD layer, which would
reduce the observed torque in these bilayers. In addition, we find a field-like
spin-torque conductivity of comparable magnitude to control
MoS$_{2}$/permalloy/Al$_{2}$O$_{3}$ devices, indicating only a minor role of
the MoS$_{2}$ layer. Finally, we find a linear dependence of the SOT
conductivity on the Hall bar leg/channel width ratio of our devices, indicating
that the Hall bar dimensions are of significant importance for the reported SOT
strength. Our results accentuate the importance of delicate details, like
device asymmetry, Hall bar dimensions, and self-torque generation, for the
correct disentanglement of the microscopic origins underlying the SOTs,
essential for future energy-efficient spintronic applications.",2303.03892v2
2003-07-21,Dynamics of ferromagnetic nanomagnets with vortex or single-domain configuration,"We study the dynamics of flat circular permalloy nanomagnets for 1.) magnetic
vortex and 2.) single-domain configurations, using micromagnetic simulation.
Dynamical studies for isolated vortex structures show that both the vorticity
and the central polarity of the out-of-plane component can be switched fast
(50-100 ps) and independently. Micromagnetic simulations of the switching
process in thin cylindrical Permalloy (Py) nanoparticles with an initial stable
single-domain state show nearly homogeneous single-domain behaviour followed by
excitation of spin waves.",0307503v1
2003-11-18,Domain-specific magnetization reversals on a permalloy square ring array,"We present domain-specific magnetization reversals extracted from soft x-ray
resonant magnetic scattering measurement on a permalloy square ring array. The
extracted domain-specific hysteresis loops reveal that the magnetization of the
domain parallel to the field is strongly pinned, while those of other domains
rotate continuously. In comparison with the micromagnetic simulation, the
hysteresis loop on the pinned domain indicates a possibility of the coexistence
of the square rings with the vortex and onion states.",0311417v1
2006-04-05,Anisotropy of Magnetization Reversal and Magnetoresistance in Square Arrays of Permalloy Nano-Rings,"Magnetization reversal mechanisms and impact of magnetization direction are
studied in square arrays of interconnected circular permalloy nanorings using
MOKE, local imaging, numerical simulations and transport techniques.",0604132v1
2007-02-02,Current-induced magnetic vortex core switching in a Permalloy nanodisk,"We report on the switching of a magnetic vortex core in a sub-micron
Permalloy disk, induced by a short current pulse applied in the film plane.
Micromagnetic simulations including the adiabatic and non-adiabatic spin-torque
terms are used to investigate the current-driven magnetization dynamics. We
predict that a core reversal can be triggered by current bursts a tenth of a
nanosecond long. The vortex core reversal process is found to be the same as
when an external field pulse is applied. The control of a vortex core's
orientation using current pulses introduces the technologically relevant
possibility to address individual nanomagnets within dense arrays.",0702048v1
2008-02-06,Self-organized plane arrays of metallic magnetic elements,"We studied the dynamic magnetic properties of plane periodical arrays of
circular permalloy nano-dots fabricated using a self-organized mask formed by
polysterene nanospheres on the surface of a Permalloy film. Conventional
(microwave cavity) and broadband coplanar-line ferromagnetic resonance setups
were used for the measurements. We found several well resolved resonance peaks.
This result shows that the self-organized mask fabrication technique is able to
produce high-quality samples with small dispersion of geometrical and magnetic
parameters.",0802.0731v1
2008-07-11,Probing the spin polarization of current by soft X-ray imaging of current-induced magnetic vortex dynamics,"Time-resolved soft X-ray transmission microscopy is applied to image the
current-induced resonant dynamics of the magnetic vortex core realized in a
micronsized Permalloy disk. The high spatial resolution better than 25 nm
enables us to observe the resonant motion of the vortex core. The result also
provides the spin polarization of the current to be 0.67 +/-0.16 for Permalloy
by fitting the experimental results with an analytical model in the framework
of the spin-transfer torque.",0807.1782v1
2008-11-03,Domain wall propagation in Permalloy nanowires with a thickness gradient,"The domain wall nucleation and motion processes in Permalloy nanowires with a
thickness gradient along the nanowire axis have been studied. Nanowires with
widths, w = 250 nm to 3 um and a base thickness of t = 10 nm were fabricated by
electron-beam lithography. The magnetization hysteresis loops measured on
individual nanowires are compared to corresponding nanowires without a
thickness gradient. The Hc vs. t/w curves of wires with and without a thickness
gradient are discussed and compared to micromagnetic simulations. We find a
metastability regime at values of w, where a transformation from transverse to
vortex domain wall type is expected.",0811.0245v2
2009-05-13,Observation of spin-wave propagation in permalloy microstripes,"We report on the propagation of spin waves in permalloy microstripes. By
means of scanning Kerr microscopy combined with continuous microwave
excitation, we detect the time evolution of spin-wave interference patterns in
an external magnetic field. Assuming transverse spin-wave quantization we can
directly measure the amplitude, phase velocity and damping for the
corresponding transversal wave mode numbers m. We find that the spin-wave
interference pattern is dominated by m=0 and m=2 with phase velocities v_0=71
km/s and v_2=47 km/s, respectively.",0905.2172v1
2009-06-12,Six-fold configurational anisotropy and magnetic reversal in nanoscale Permalloy triangles,"Six-fold configurational anisotropy was studied in Permalloy triangles, in
which the shape symmetry order yields two energetically non-degenerate
micromagnetic configurations of the spins, the so-called ""Y"" and ""buckle""
states. A twelve pointed switching astroid was measured using magneto-optical
experiments and successfully reproduced numerically, with different polar
quadrants identified as specific magnetic transitions, thereby giving a
comprehensive view of the magnetic reversal in these structures. A detailed
analysis highlighted the necessity to include the physical rounding of the
structures in the simulations to account for the instability of the Y state.",0906.2322v1
2009-07-14,Localized ferromagnetic resonance force microscopy in permalloy-cobalt films,"We report Ferromagnetic Resonance Force Microscopy (FMRFM) experiments on a
justaposed continuous films of permalloy and cobalt. Our studies demonstrate
the capability of FMRFM to perform local spectroscopy of different
ferromagnetic materials. Theoretical analysis of the uniform resonance mode
near the edge of the film agrees quantitatively with experimental data. Our
experiments demonstrate the micron scale lateral resolution in determining
local magnetic properties in continuous ferromagnetic samples.",0907.2415v1
2009-09-09,Rapid Domain Wall Motion in Permalloy Nanowires Excited by Spin-Polarized Current Applied Perpendicular to the Nanowire,"We study domain wall (DW) dynamics in permalloy nanowires excited by
alternating spin-polarized current applied perpendicular to the nanowire. Spin
torque ferromagnetic resonance measurements reveal that DW oscillations at a
pinning site in the nanowire can be excited with velocities as high as 800 m/s
at current densities below 10$^7$ A/cm$^2$.",0909.1822v4
2009-11-26,Macrospin limit and configurational anisotropy in nanoscale Permalloy triangles,"In Permalloy submicron triangles, configurational anisotropy - a higher-order
form of shape anisotropy - yields three equivalent easy axes, imposed by the
structures' symmetry order. Supported by micromagnetic simulations, an
experimental method was devised to evaluate the nanostructure dimensions for
which a Stoner-Wohlfarth type of reversal could be used to describe this
particular magnetic anisotropy. In this regime, a straightforward procedure
using an in-plane rotating field allowed us to quantify experimentally the
six-fold anisotropy fields for triangles of different thicknesses and sizes.",0911.5121v1
2011-03-16,Anomalous-Nernst and anisotropic magnetoresistive heating in a lateral spin valve,"We measured the anomalous-Nernst effect and anisotropic magnetoresistive
heating in a lateral multiterminal Permalloy/Copper spin valve using
all-electrical lock-in measurements. To interpret the results, a
three-dimensional thermoelectric finite-element-model is developed. Using this
model, we extract the heat profile which we use to determine the anomalous
Nernst coefficient of Permalloy Rn=0.13 and also determine the maximum angle of
theta=8 degrees of the magnetization prior to the switching process when an
opposing non-collinear 10$^{\circ}$ magnetic field is applied.",1103.3305v1
2011-12-03,Microwave-induced DC Signal in a Permalloy Thin Strip at Low Applied Magnetic Field,"We investigated the ferromagnetic resonance signals in a polycrystalline
permalloy thin strip under in-plane low static magnetic field. A series of DC
voltages, which contain ferromagnetic resonance or spin wave resonance signals,
were measured by inducing microwave frequencies greater than 10 gigahertz. The
resonant signals measured in low magnetic field show different properties from
those detected in high field condition. Based on the theory of DC effects in
ferromagnetic resonance and the experimental data of anisotropic
magnetoresistance, a quantitative model was proposed. We found that the shape
anisotropy significantly affects magnetization, and distorts the resonant
signals in low field condition.",1112.0610v1
2012-10-30,Microwave assisted resonant domain wall nucleation in permalloy nanowires,"We have designed a system to study microwave assisted domain wall nucleation
in permalloy nanowires. We find a substantial decrease in the nucleation field
when microwave fields are applied, in comparison to pulse fields. A clear
resonance peak is observed in the frequency dependence of the nucleation field,
which coincides with the uniform mode ferromagnetic resonance frequency. Owing
to the well-defined nucleation process, the switching field distribution is
small in contrast to previous reports. Our results show that localized
microwave field provides an efficient tool for injecting domain walls into
magnetic nanowires.",1210.7875v1
2013-03-07,Thickness dependence of the degree of spin polarization of the electrical current in permalloy thin films,"Spin-polarized electrical transport is investigated in $
Al_{2}O_{3}/Ni_{80}Fe_{20}/Al_{2}O_{3}$ thin films for permalloy thickness
between 6 and 20nm. The degree of spin-polarization of the current flowing in
the plane of the film is measured through the current induced spin wave Doppler
shift. We find that it decreases as the film thickness decreases, from 0.72 at
20nm to 0.46 at 6nm. This decrease is attributed to a spin depolarization
induced by the film surfaces. A model is proposed which takes into account the
contributions of the different sources of electron scattering (alloy disorder,
phonons, thermal magnons, grain boundaries, film surfaces) to the measured
spin-dependent resistivities.",1303.1692v1
2013-08-14,Electrical Detection of Spin Wave Resonance in a Permalloy Thin Strip,"We investigated the microwave-induced DC response of spin wave resonance
(SWR) in a permalloy thin strip via electrical detection. Our experimental
results obtained by sweeping the external field reveal that: 1. the amplitude
of SWR signals depend on the direction of external field and, 2. unlike the DC
response of ferromagnetic resonance, SWR spectra are always anti-symmetrical.
The spin dynamics are discussed based on these unusual signals in resonant
condition.",1308.3069v1
2014-04-04,Control of domain wall motion at vertically etched nanotrench in ferromagnetic nanowires,"We study field-induced domain wall motion in permalloy nanowires with
vertically etched nanotrench pinning site. Micromagnetic simulations and
electrical measurements are employed to characterize the pinning potential at
the nanotrench. It is found that the potential profile for a transverse wall
significantly differs from that of a vortex wall, and there is a correlation
between the pinning strength and the potential profile. Reliable domain wall
pinning and depinning is experimentally observed from a nanotrench in permalloy
nanowires. This demonstrates the suitability of the proposed nanotrench pinning
sites for domain wall device applications.",1404.1138v1
2015-03-16,Detection of spin waves in permalloy using planar Hall effect,"Rectification of microwave oscillations of magnetization in a permalloy film
is realized using planar Hall effect. Two different rectified signals are
obtained: a signal from the linearly excited uniform magnetization precession
at the frequency of the external pumping and a signal from the pairs of
contra-propagating short-wavelength spin waves parametrically generated at a
half of the pumping frequency. The second, most unusual, rectified signal is
caused by the uniform component of the dynamic magnetization created due to the
interference of the phase correlated pairs of parametric spin waves.",1503.04638v1
2017-11-30,Spin glass transition in a thin-film NiO/Permalloy bilayer,"We experimentally study magnetization aging in a thin-film NiO/Permalloy
bilayer. Aging characteristics are nearly independent of temperature below the
exchange bias blocking temperature, but rapidly vary above it. The dependence
on the magnetic history qualitatively changes across this temperature. The
observed behaviors are consistent with the spin glass transition at the
exchange bias blocking temperature, with significant implications for magnetism
and magnetoelectronic phenomena in antiferromagnet/ferromagnet bilayers.",1711.11544v1
2018-07-27,Thick Permalloy films for the imaging of spin texture dynamics in perpendicularly magnetized systems,"We demonstrated that thick Permalloy films exhibiting a weak growth-induced
perpendicular magnetic anisotropy can be employed as an ideal test system for
the investigation of gyration dynamics in topologically trivial and non-trivial
magnetic states ranging from an isolated magnetic skyrmion to more complex
n$\pi$ spin configurations.",1807.10654v1
2016-03-02,Ferromagnetic resonance in submicron permalloy stripes,"We present the results of systematic experimental investigations and
micromagnetic simulations for the ferromagnetic resonance in rectangular
permalloy microstripes. It is shown that the resonant magnetization
oscillations have a complex spatial structure including a quasi-homogeneous
precession, lateral spin-wave resonances and localized edge modes, which
strongly depend on sample orientation in an external magnetic field.",1603.00694v1
2019-09-05,Magnetically dependent plasmon drag in permalloy structures,"Significant photovoltages are observed in permalloy grating-like structures
in response to pulsed laser light illumination. Electric signals are enhanced
at plasmon resonance conditions and show a clear dependence on the magnetic
field with a characteristic hysteresis. Estimations show that the effect could
not be explained solely by the laser-induced heating. Alternative mechanisms
are discussed.",1909.02675v3
2021-03-15,Ferromagnetic Resonance in Permalloy Metasurfaces,"Permalloy films with one-dimensional (1D) profile modulation of submicron
periodicity are fabricated based on commercially available DVD-R discs and
studied using ferromagnetic resonance (FMR) method and micromagnetic numerical
simulations. The main resonance position shows in-plane angular dependence
which is strongly reminiscent of that in ferromagnetic films with uniaxial
magnetic anisotropy. The main signal and additional low field lines are
attributed to multiple standing spin wave resonances defined by the grating
period. The results may present interest in magnetic metamaterials and
magnonics applications.",2103.08704v1
2022-09-22,Barkhausen noise from formation of 360$^{\circ}$ domain walls in disordered permalloy thin films,"Barkhausen noise in disordered ferromagnets is typically understood to
originate primarily from jerky field-driven motion of domain walls. We study
the magnetization reversal process in disordered permalloy thin films using
micromagnetic simulations, and find that the magnetization reversal process
consists of gradual formation of immobile 360$^{\circ}$ domain walls via a
sequence of localized magnetization rotation events. The density of
360$^{\circ}$ domain walls formed within the sample as well as the statistical
properties of the Barkhausen jumps are controlled by the disorder strength.",2209.10847v2
2023-03-28,Role of intersublattice exchange interaction on ultrafast longitudinal and transverse magnetization dynamics in Permalloy,"We report about element specific measurements of ultrafast demagnetization
and magnetization precession damping in Permalloy (Py) thin films.
Magnetization dynamics induced by optical pump at $1.5$eV is probed
simultaneously at the $M_{2,3}$ edges of Ni and Fe with High order Harmonics
for moderate demagnetization rates (less than $50$%). The role of the
intersublattice exchange interaction on both longitudinal and transverse
dynamics is analyzed with a Landau Lifshitz Bloch description of
ferromagnetically coupled Fe and Ni sublattices. It is shown that the
intersublattice exchange interaction governs the dissipation during
demagnetization as well as precession damping of the magnetization vector.",2303.15837v1
2005-04-16,Spin-Transfer Excitations of Permalloy Nanopillars for Large Applied Currents,"Using measurements of the spectra of microwave-frequency resistance
oscillations, we determine the phase diagram of magnetic excitations caused by
torques from DC spin-polarized currents in (thin permalloy)/copper/(thick
permalloy) multilayer samples. We extend the measurements to larger values of
current than have been reported previously. We find several additional modes
that we are able to identify with motion of the thick magnetic layer as well as
the thin one. Peaks in the microwave spectra at multiple frequencies suggest
that spatially non-uniform dynamical states can be important in some
circumstances. We compare the experimental phase diagram with simple
theoretical models and achieve a good qualitative agreement.",0504402v1
2010-06-29,Magnetic properties of exchange biased and of unbiased oxide/permalloy thin layers: a ferromagnetic resonance and Brillouin scattering study,"Microstrip ferromagnetic resonance and Brillouin scattering are used to
provide a comparative determination of the magnetic parameters of thin
permalloy layers interfaced with a non-magnetic (Al2O3) or with an
antiferromagnetic oxide (NiO). It is shown that the perpendicular anisotropy is
monitored by an interfacial surface energy term which is practically
independent of the nature of the interface. In the investigated interval of
thicknesses (5-25 nm) the saturation magnetisation does not significantly
differ from the reported one in bulk permalloy. In-plane uniaxial anisotropy
and exchange-bias anisotropy are also derived from this study of the dynamic
magnetic excitations and compared to our independent evaluations using
conventional magnetometry",1006.5598v1
2013-04-08,Temperature dependence of spin polarization in ferromagnetic metals using lateral spin valves,"A high reproducibility in the performance of cobalt/copper and
permalloy/copper lateral spin valves with transparent contacts is obtained by
optimizing the interface quality and the purity of copper. This allows us to
study comprehensively the spin injection properties of both ferromagnetic
materials, as well as the spin transport properties of copper, which are not
affected by the used ferromagnetic material, leading to long spin diffusion
lengths. Spin polarizations of permalloy and cobalt are obtained as a function
of temperature. Analysis of the temperature dependence of both the spin
polarization and conductivity of permalloy using the standard two-channel model
for ferromagnetic metals suggests that a correction factor of ~2 is needed for
the spin polarization values obtained by lateral spin valve experiments.",1304.2123v3
2015-02-28,Large amplitude vortex gyration in Permalloy/Bi$_2$Se$_3$-like heterostructures,"We consider the excitation of large amplitude gyrotropic vortex core
precession in a Permalloy nanodisk by the torques originating from the in-plane
microwave current flowing along the interface of the Permalloy/Bi$_2$Se$_3$
heterostructures, in which the huge charge-to-spin conversion ratio is observed
\cite{Mellnik-2014}. We consider analytically and by micromagnetic modelling
the dependence of this excitation on the frequency and magnitude of the
microwave current. The analogies of the vortex dynamics and the Landau phase
transitions theory is demonstrated. These findings open the possibility to
excite gyrotropic vortex motion with the current densities far lower than by
any other means.",1503.00089v3
2015-08-21,Radiative damping in wave guide based FMR measured via analysis of perpendicular standing spin waves in sputtered Permalloy films,"The damping $\alpha$ of the spinwave resonances in 75 nm, 120 nm, and 200nm
-thick Permalloy films is measured via vector-network-analyzer
ferromagnetic-resonance (VNA-FMR) in the out-of-plane geometry. Inductive
coupling between the sample and the waveguide leads to an additional radiative
damping term. The radiative contribution to the over-all damping is determined
by measuring perpendicular standing spin waves (PSSWs) in the Permalloy films,
and the results are compared to a simple analytical model. The damping of the
PSSWs can be fully explained by three contributions to the damping: The
intrinsic damping, the eddy-current damping, and the radiative damping. No
other contributions were observed. Furthermore, a method to determine the
radiative damping in FMR measurements with a single resonance is suggested.",1508.05265v1
2018-01-22,Spin-orbit torques in NbSe$_2$/Permalloy bilayers,"We present measurements of current-induced spin-orbit torques generated by
NbSe$_2$, a fully-metallic transition-metal dichalcogenide material, made using
the spin-torque ferromagnetic resonance (ST-FMR) technique with
NbSe$_{2}$/Permalloy bilayers. In addition to the out-of-plane Oersted torque
expected from current flow in the metallic NbSe$_{2}$ layer, we also observe an
in-plane antidamping torque with torque conductivity $\sigma_{S} \approx 10^{3}
(\hbar / 2e)$($\Omega$m)$^{-1}$ and indications of a weak field-like
contribution to the out-of-plane torque oriented opposite to the Oersted
torque. Furthermore, in some samples we also measure an in-plane field-like
torque with the form $\hat{m} \times \hat{z}$, where $\hat{m}$ is the Permalloy
magnetization direction and $\hat{z}$ is perpendicular to the sample plane. The
size of this component varies strongly between samples and is not correlated
with the NbSe$_{2}$ thickness. A torque of this form is not allowed by the bulk
symmetries of NbSe$_{2}$, but is consistent with symmetry breaking by a
uniaxial strain that might result during device fabrication.",1801.07281v1
2019-02-10,Spin dynamics of anisotropic azimuthal modes in heterogeneous magnetic nanodisks,"It is well known that azimuthal spin wave modes of magnetic vortex state in
permalloy nanodisks have circular symmetry. Intuitively, magnetic materials
having magnetocrystalline anisotropy is not compatible with the circular
symmetry of the azimuthal modes. In this article, however, we report cubic
azimuthal modes in heterogeneous nanodisks consisting of a permalloy core and a
Fe shell. The fourfold symmetry of azimuthal modes is due to the exchange, and
magneto-static, interactions between the permalloy core and the Fe shell. In
comparison to results of circular azimuthal mode, the vortex switching occurs
considerably faster under the excitation of cubic azimuthal mode. The gyration
path of vortex core turns into square under the influence of induced cubic
anisotropy in the Py region. We find out periodic oscillation of the vortex
core size and the gyration speed as well. Our findings may offer a new route
for spintronic applications using heterogeneous magnetic nanostructures.",1902.03536v1
2019-02-26,Strong magnon-photon coupling in ferromagnet-superconducting resonator thin-film devices,"We demonstrate strong magnon-photon coupling of a thin-film permalloy device
fabricated on a coplanar superconducting resonator. A coupling strength of
0.152 GHz and a cooperativity of 68 are found for a 30-nm-thick permalloy
stripe. The coupling strength is tunable by rotating the biasing magnetic field
or changing the volume of permalloy. We also observe an enhancement of
magnon-photon coupling in the nonlinear regime of the superconducting
resonator, which is mediated by the nucleation of dynamic flux vortices. Our
results demonstrate a critical step towards future integrated hybrid systems
for quantum magnonics and on-chip coherent information transfer.",1902.09715v1
2019-03-07,Interplay between intra- and inter-nanowires dynamic dipolar interactions in the spin wave band structure of Py/Cu/Py nanowires,"We have studied both experimentally and theoretically the reprogrammable spin
wave band structure in Permalloy(10nm)/Cu(5nm)/Permalloy(30nm) nanowire arrays
of width w=280 nm and inter-wire separation in the range from 80 to 280 nm. We
found that, depending on the inter-wire separation, the anti-parallel
configuration, where the magnetizations of the two Permalloy layers point in
opposite directions, is stabilized over specific magnetic field ranges thus
enabling us to directly compare the band structure with that of the parallel
alignment. We show that collective spin waves of the Bloch type propagate
through the arrays with different magnonic bandwidths as a consequence of the
interplay between the intra- and inter-nanowire dynamic dipolar interactions. A
detailed understanding, e.g. whether they have a stationary or propagating
character, is achieved by considering the phase relation (in-phase or
out-of-phase) between the dynamic magnetizations in the two ferromagnetic
layers and their average value. This work opens the path to magnetic
field-controlled reconfigurable layered magnonic crystals that can be used for
future nanoscale magnon spintronic devices.",1903.02935v1
2019-09-03,Self-induced inverse spin Hall effect in ferromagnets: demonstration through non-monotonous temperature-dependence in permalloy,"We investigated the self-induced inverse spin Hall effect in ferromagnets.
Temperature (T), thickness (t) and angular-dependent measurements of transverse
voltage in spin pumping experiments were performed with permalloy films.
Results revealed non-monotonous T-dependence of the self-induced transverse
voltage. Qualitative agreement was found with first-principle calculations
unravelling the skew scattering, side-jump, and intrinsic contributions to the
T-dependent spin Hall conductivity. Experimental data were similar whatever the
material in contact with permalloy (oxides or metals), and revealed an increase
of produced current with t, demonstrating a bulk origin of the effect.",1909.00976v1
2022-01-26,Memristive effects in nanopatterned permalloy Kagomé array,"We study memristive effects in Kagom\'{e} nanopatterned permalloy. We observe
that at low frequencies a thermistor effect is present, a phenomenon arising
due to the lithography and absent in similar experiments for thin films.
However, we also show via an independent anisotropic magnetoresistive study
that a small hysteresis accounting for 1% of the effect is not attributable to
a thermistive effect. Such effect is also confirmed by a careful subtraction
scheme between nearby thermal hysteresis. In the millihertz regime, an
effective model is provided to describe the experimental results for the
thermistor, showing that there should be a crossover from the millihertz to the
gigahertz, from a thermistor to an memresistive effect for nanopatterned
permalloy.",2201.11200v1
2023-02-04,Tailoring magnetic hysteresis of Fe-Ni permalloy by additive manufacturing: Multiphysics-multiscale simulations of process-property relationships,"Designing the microstructure of Fe-Ni permalloy by additive manufacturing
(AM) opens new avenues to tailor the materials' magnetic properties. Yet,
AM-produced parts suffer from spatially inhomogeneous thermal-mechanical and
magnetic responses, which are less investigated in terms of process simulation
and modeling schemes. Here we present a powder-resolved multiphysics-multiscale
simulation scheme for describing magnetic hysteresis in materials produced via
AM. The underlying physical processes are explicitly considered, including the
coupled thermal-structural evolution, chemical order-disorder transitions, and
associated thermo-elasto-plastic behaviors. The residual stress is identified
as the key thread in connecting the physical processes and in-process phenomena
across scales. By employing this scheme, we investigate the dependence of the
fusion zone size, the residual stress and plastic strain, and the magnetic
hysteresis of AM-produced Fe21.5Ni78.5 permalloy on beam power and scan speed.
Simulation results also suggest a phenomenological relation between magnetic
coercivity and average residual stress, which can guide the magnetic hysteresis
design of soft magnetic materials by choosing appropriate AM-process
parameters.",2302.02217v1
2015-09-15,Third type of domain wall in soft magnetic nanostrips,"Magnetic domain walls (DWs) in nanostructures are low-dimensional objects
that separate regions with uniform magnetisation. Since they can have different
shapes and widths, DWs are an exciting playground for fundamental research, and
became in the past years the subject of intense works, mainly focused on
controlling, manipulating, and moving their internal magnetic configuration. In
nanostrips with in-plane magnetisation, two DWs have been identified: in thin
and narrow strips, transverse walls are energetically favored, while in thicker
and wider strips vortex walls have lower energy. The associated phase diagram
is now well established and often used to predict the low-energy magnetic
configuration in a given magnetic nanostructure. However, besides the
transverse and vortex walls, we find numerically that another type of wall
exists in permalloy nanostrips. This third type of DW is characterised by a
three-dimensional, flux closure micromagnetic structure with an unusual length
and three internal degrees of freedom. Magnetic imaging on
lithographically-patterned permalloy nanostrips confirms these predictions and
shows that these DWs can be moved with an external magnetic field of about 1mT.
An extended phase diagram describing the regions of stability of all known
types of DWs in permalloy nanostrips is provided.",1509.04762v1
2016-01-29,Magnetic domain-wall dynamics in wide permalloy strips,"Domain walls in soft permalloy strips may exhibit various equilibrium
micromagnetic structures depending on the width and thickness of the strip,
ranging from the well-known transverse and vortex walls in narrow and thin
strips to double and triple vortex walls recently reported in wider strips [V.
Est\'evez and L. Laurson, Phys. Rev. B {\bf 91}, 054407 (2015)]. Here we
analyze the field driven dynamics of such domain walls in permalloy strips of
widths from 240 nm up to 6 $\mu$m, using the known equilibrium domain wall
structures as initial configurations. Our micromagnetic simulations show that
the domain wall dynamics in wide strips is very complex, and depends strongly
on the geometry of the system, as well as on the magnitude of the driving
field. We discuss in detail the rich variety of the dynamical behaviors found,
including dynamic transitions between different domain wall structures,
periodic dynamics of a vortex core close to the strip edge, transitions towards
simpler domain wall structures of the multi-vortex domain walls controlled by
vortex polarity, and the fact that for some combinations of the strip geometry
and the driving field the system cannot support a compact domain wall.",1601.08060v1
2018-04-11,Thermographic measurements of spin-current-induced temperature modulation in metallic bilayers,"Spin-to-heat current conversion effects have been investigated in bilayer
films consisting of a paramagnetic metal (PM; Pt, W, or Ta) and a ferromagnetic
metal (FM; CoFeB or permalloy). When a charge current is applied to the PM/FM
bilayer film, a spin current is generated across the PM/FM interface owing to
the spin Hall effect in PM. The spin current was found to exhibit cooling and
heating features depending on the sign of the spin Hall angle of PM, where the
spin-current-induced contribution is estimated by subtracting the contribution
of the anomalous Ettingshausen effect in FM monolayer films. We also found that
the magnitude of the spin-current-induced temperature modulation in the
Pt/CoFeB film is greater than but comparable to that in the Pt/permalloy film,
although the spin dependence of the Peltier coefficient for CoFeB is expected
to be greater than that for permalloy. We discuss the origin of the observed
behaviors with the aid of model calculations; the signals in the PM/FM films
may contain the contributions not only from the electron-driven spin-dependent
Peltier effect but also from the magnon-driven spin Peltier effect.",1804.04068v1
2017-03-11,Spin-wave dynamics in Permalloy/Cobalt magnonic crystals in the presence of a non-magnetic spacer,"In this paper, we theoretically study the influence of a non-magnetic spacer
between ferromagnetic dots and ferromagnetic matrix on the frequency dispersion
of the spin wave excitations in two-dimensional bi-component magnonic crystals.
By means of the dynamical matrix method we investigate structures inhomogeneous
across the thickness represented by square arrays of Cobalt or Permalloy dots
in a Permalloy matrix. We show that the introduction of a non-magnetic spacer
significantly modifies the total internal magnetic field especially at the
edges of the grooves and dots. This permits the manipulation of the magnonic
band structure of spin waves localized either at the edges of the dots or in
matrix material at the edges of grooves. According to the micromagnetic
simulations two types of end modes were found. The corresponding frequencies
are significantly influenced by the end modes localization region. We also show
that, with the use of a single ferromagnetic material, it is possible to design
a magnonic crystal preserving properties of bi-component magnonic crystals and
magnonic antidot lattices. Finally, the influence of the non-magnetic spacers
on the technologically relevant parameters like group velocity and magnonic
band width are discussed.",1703.03978v1
2021-05-05,Ni$_{80}$Fe$_{20}$ Nanotubes with Optimized Spintronic Functionalities Prepared by Atomic Layer Deposition,"Permalloy Ni$_{80}$Fe$_{20}$ is one of the key magnetic materials in the
field of magnonics. Its potential would be further unveiled if it could be
deposited in three dimensional (3D) architectures of sizes down to the
nanometer. Atomic Layer Deposition, ALD, is the technique of choice for
covering arbitrary shapes with homogeneous thin films. Early successes with
ferromagnetic materials include nickel and cobalt. Still, challenges in
depositing ferromagnetic alloys reside in the synthesis via decomposing the
consituent elements at the same temperature and homogeneously. We report
plasma-enhanced ALD to prepare permalloy Ni$_{80}$Fe$_{20}$ thin films and
nanotubes using nickelocene and iron(III) tert-butoxide as metal precursors,
water as the oxidant agent and an in-cycle plasma enhanced reduction step with
hydrogen. We have optimized the ALD cycle in terms of Ni:Fe atomic ratio and
functional properties. We obtained a Gilbert damping of 0.013, a resistivity of
28 $\mu\Omega$cm and an anisotropic magnetoresistance effect of 5.6 $\%$ in the
planar thin film geometry. We demonstrate that the process also works for
covering GaAs nanowires, resulting in permalloy nanotubes with high aspect
ratios and diameters of about 150 nm. Individual nanotubes were investigated in
terms of crystal phase, composition and spin-dynamic response by microfocused
Brillouin Light Scattering. Our results enable NiFe-based 3D spintronics and
magnonic devices in curved and complex topology operated in the GHz frequency
regime.",2105.01969v1
2021-06-04,Readout of a antiferromagnetic spintronics systems by strong exchange coupling of Mn2Au and Permalloy,"In antiferromagnetic spintronics, the read-out of the staggered magnetization
or Neel vector is the key obstacle to harnessing the ultra-fast dynamics and
stability of antiferromagnets for novel devices. Here, we demonstrate strong
exchange coupling of Mn2Au, a unique metallic antiferromagnet that exhibits
Neel spin-orbit torques, with thin ferromagnetic Permalloy layers. This allows
us to benefit from the well-estabished read-out methods of ferromagnets, while
the essential advantages of antiferromagnetic spintronics are retained. We show
one-to-one imprinting of the antiferromagnetic on the ferromagnetic domain
pattern. Conversely, alignment of the Permalloy magnetization reorients the
Mn2Au Neel vector, an effect, which can be restricted to large magnetic fields
by tuning the ferromagnetic layer thickness. To understand the origin of the
strong coupling, we carry out high resolution electron microscopy imaging and
we find that our growth yields an interface with a well-defined morphology that
leads to the strong exchange coupling.",2106.02333v1
2023-06-26,Control of the asymmetric band structure in Mn2Au by a ferromagnetic driver layer,"Hard X-ray angle-resolved photoemission spectroscopy reveals the
momentum-resolved band structure in an epitaxial Mn2Au(001) film capped by a 2
nm thick ferromagnetic Permalloy layer. By magnetizing the Permalloy capping
layer, the exceptionally strong exchange bias aligns the Neel vector in the
Mn2Au(001) film accordingly. Uncompensated interface Mn magnetic moments in
Mn2Au were identified as the origin of the exchange bias using X-ray magnetic
circular dichroism in combination with photoelectron emission microscopy. Using
time-of-flight momentum microscopy, we measure the asymmetry of the band
structure in Mn2Au resulting from the homogeneous orientation of the Neel
vector. Comparison with theory shows that the Neel vector, determined by the
magnetic moment of the top Mn layer, is antiparallel to the Permalloy
magnetization. The experimental results demonstrate that hard X-ray
photoemission spectroscopy can measure the band structure of epitaxial layers
beneath a metallic capping layer and corroborate the asymmetric band structure
in Mn2Au that was previously inferred only indirectly.",2306.14713v1
2023-11-07,Revealing the ultra-fast domain wall motion in Manganese Gold through permalloy capping,"Antiferromagnets offer much faster dynamics compared to their ferromagnetic
counterparts but their order parameter is extremely difficult to detect and
control. So far, controlling the N\'eel order parameter electrically is limited
to only very few materials where N\'eel spin-orbit torques are allowed by
symmetry. In this work, we show that coupling a thin ferromagnet (permalloy)
layer on top of an antiferromagnet (Mn$_2$Au) solves a major roadblock -- the
controlled reading, writing, and manipulation of antiferromagnetic domains. We
confirm by atomistic spin dynamics simulations that the domain wall patterns in
the Mn$_2$Au are imprinted on the permalloy, therefore allowing for indirect
imaging of the N\'eel order parameter. Our simulations show that the coupled
domain wall structures in Mn$_2$Au-Py bilayers can be manipulated by either
acting on the N\'eel order parameter via N\'eel spin-orbit torques or by acting
on the magnetisation (the ferromagnetic order parameter) via magnetic fields.
In both cases, we predict ultra-high domain wall speeds on the order of 8.5
km/s. Thus, employing a thin ferromagnetic layer has the potential to easily
control the N\'eel order parameter in antiferromagnets even where N\'eel
spin-orbit torques are forbidden by symmetry. The controlled manipulation of
the antiferromagnetic order parameter provides a promising basis for the
development of high-density storage and efficient computing technologies
working in the THz regime.",2311.04305v1
2003-05-12,A Novel Broadband Measurement Method for the Magnetoimpedance of Ribbons and Thin Films,"A novel broad-band measurement method of the MI in thin films and ribbons is
presented. It is based on the automated measurement of the reflection
coefficient of a cell loaded with the sample. Illustrative results obtained
with a permalloy multilayer thin film are presented and discussed.",0305259v1
2004-04-07,Influence of point defects on magnetic vortex structures,"We employed micro-Hall magnetometry and micromagnetic simulations to
investigate magnetic vortex pinning at single point defects in individual
submicron-sized permalloy disks. Small ferromagnetic particles containing
artificial point defects can be fabricated by using an image reversal electron
beam lithography process. Corresponding micromagnetic calculations, modeling
the defects within the disks as holes, give reasonable agreement between
experimental and simulated pinning and depinning field values.",0404159v1
2007-05-15,Controlled vortex core switching in a magnetic nanodisk by a rotating field,"The switching process of the vortex core in a Permalloy nanodisk affected by
a rotating magnetic field is studied theoretically. A detailed description of
magnetization dynamics is obtained by micromagnetic simulations.",0705.2046v2
2016-07-06,Introduction of spin-orbit interaction into graphene with hydrogenation,"Introduction of spin-orbit interaction (SOI) into graphene with weak
hydrogenation ($\sim$0.1\%) by dissociation of hydrogen silsesquioxane resist
has been confirmed through the appearance of inverse spin Hall effect. The spin
current was produced by spin injection from permalloy electrodes excluding
non-spin relating experimental artifact.",1607.01558v1
2023-02-28,Optimization of Permalloy properties for magnetic field sensors using He$^+$ irradiation,"Permalloy, despite being a widely utilized soft magnetic material, still
calls for optimization in terms of magnetic softness and magnetostriction for
its use in magnetoresistive sensor applications. Conventional annealing methods
are often insufficient to locally achieve the desired properties for a narrow
parameter range. In this study, we report a significant improvement of the
magnetic softness and magnetostriction in a 30 nm Permalloy film after He$^+$
irradiation. Compared to the as-deposited state, the irradiation treatment
reduces the induced anisotropy by a factor ten and the hard axis coercivity by
a factor five. In addition, the effective magnetostriction of the film is
significantly reduced by a factor ten - below $1\times10^{-7}$ - after
irradiation. All the above mentioned effects can be attributed to the isotropic
crystallite growth of the Ni-Fe alloy and to the intermixing at the magnetic
layer interfaces under light ion irradiation. We support our findings with
X-ray diffraction analysis of the textured Ni$_{81}$Fe$_{19}$ alloy.
Importantly, the sizable magnetoresistance is preserved after the irradiation.
Our results show that compared to traditional annealing methods, the use of
He$^+$ irradiation leads to significant improvements in the magnetic softness
and reduces strain cross sensitivity in Permalloy films required for 3D
positioning and compass applications. These improvements, in combination with
the local nature of the irradiation process make our finding valuable for the
optimization of monolithic integrated sensors, where classic annealing methods
cannot be applied due to complex interplay within the components in the device.",2302.14455v2
2000-07-31,Electrical transport properties of bulk Ni$_{c}$Fe$_{1-c}$ alloys and related spin-valve systems,"Within the Kubo-Greenwood formalism we use the fully relativistic,
spin-polarized, screened Korringa-Kohn-Rostoker method together with the
coherent-potential approximation for layered systems to calculate the
resistivity for the permalloy series Ni$_{c}$Fe$_{1-c}$. We are able to
reproduce the variation of the resistivity across the entire series; notably
the discontinuous behavior in the vicinity of the structural phase transition
from bcc to fcc. The absolute values for the resistivity are within a factor of
two of the experimental data. Also the giant magnetoresistance of a series of
permalloy-based spin-valve structures is estimated; we are able to reproduce
the trends and values observed on prototypical spin-valve structures.",0007507v1
2001-11-06,Spin injection and spin accumulation in permalloy-copper mesoscopic spin valves,"We study the electrical injection and detection of spin currents in a lateral
spin valve device, using permalloy (Py) as ferromagnetic injecting and
detecting electrodes and copper (Cu) as non-magnetic metal. Our multi-terminal
geometry allows us to experimentally distinguish different magneto resistance
signals, being 1) the spin valve effect, 2) the anomalous magneto resistance
(AMR) effect and 3) Hall effects. We find that the AMR contribution of the Py
contacts can be much bigger than the amplitude of the spin valve effect, making
it impossible to observe the spin valve effect in a 'conventional' measurement
geometry. However, these 'contact' magneto resistance signals can be used to
monitor the magnetization reversal process, making it possible to determine the
magnetic switching fields of the Py contacts of the spin valve device. In a
'non local' spin valve measurement we are able to completely isolate the spin
valve signal and observe clear spin accumulation signals at T=4.2 K as well as
at room temperature. We obtain spin diffusion lengths in copper of 1 micrometer
and 350 nm at T=4.2 K and room temperature respectively.",0111092v1
2004-07-21,Detecting domain wall trapping and motion at a constriction in narrow ferromagnetic wires using perpendicular-current giant magnetoresistance,"We present a versatile method for detecting the presence and motion of a
trapped domain wall in a narrow ferromagnetic layer using
current-perpendicular-to-plane (CPP) giant magnetoresistance (MR). The CPP-MR
response to small motions of the trapped domain wall is enhanced because the
CPP current is restricted to the region of wall trapping. We use a
Permalloy/Cu/Permalloy spin valve in the shape of a long, ~500-nm-wide wire
with a constriction (notch) near its middle that acts as a trapping site for a
head-to-head domain wall. Two different notch shapes were studied, mostly at
4.2 K but also at 295K.",0407576v1
2004-12-23,Nanocrystallization and Amorphization Induced by Reactive Nitrogen Sputtering in Iron and Permalloy,"Thin films of iron and permalloy Ni80Fe20 were prepared using an Ar+N2
mixture with magnetron sputtering technique at ambient temperature. The
nitrogen partial pressure, during sputtering process was varied in the range of
0 to 100%, keeping the total gas flow at constant. At lower nitrogen pressures
RN2<33% both Fe and NiFe, first form a nanocrystalline structure and an
increase in nitrogen partail pressure results in formation of an amorphous
structure. At intermediate nitrogen partial pressures, nitrides of Fe and NiFe
were obtained while at even higher nitrogen partial pressures, nitrides
themselves became nanocrystalline or amorphous. The surface, structural and
magnetic properties of the deposited films were studied using x-ray reflection
and diffraction, transmission electron microscopy, polarized neutron
reflectivity and using a DC extraction magnetometer. The growth behavior for
amorphous film was found different as compared with poly or nanocrystalline
films. The soft-magnetic properties of FeN were improved on nanocrystallization
while those of NiFeN were degraded. A mechanism inducing nanocrystallization
and amorphization in Fe and NiFe due to reactive nitrogen sputtering is
discussed in the present article.",0412657v1
2005-09-13,Linear magnetic flux amplifier,"By measuring the critical current versus the applied magnetic field
$I_c(\Phi)$ of an Al superconducting loop enclosing a soft Permalloy magnetic
dot, we demonstrate that it is feasible to design a linear magnetic flux
amplifier for applications in superconducting quantum interference devices. The
selected dimensions of a single-domain Permalloy dot provide that the
preferential orientation of the magnetization is rotated from the perpendicular
direction. By increasing an applied magnetic field, the magnetization of the
dot coherently rotates towards the out-of-plane direction, thus providing a
flux gain and an enhancement of the sensitivity. As a result of a pronounced
shape anisotropy, the flux gain generated by the dot can be tuned by adjusting
the dimensions of the dot.",0509332v1
2006-06-09,Spin wave dynamics and the determination of intrinsic Gilbert damping in locally-excited Permalloy thin films,"Time-resolved scanning Kerr effect microscopy has been used to study
magnetization dynamics in Permalloy thin films excited by transient magnetic
pulses generated by a micrometer-scale transmission line structure. The results
are consistent with magnetostatic spin wave theory and are supported by
micromagnetic simulations. Magnetostatic volume and surface spin waves are
measured for the same specimen using different bias field orientations and can
be accurately calculated by k-space integrations over all excited plane wave
components. A single damping constant of Gilbert form is sufficient to describe
both scenarios. The nonuniform pulsed field plays a key role in the spin wave
dynamics, with its Fourier transform serving as a weighting function for the
participating modes. The intrinsic Gilbert damping parameter $\alpha$ is most
conveniently measured when the spin waves are effectively stationary.",0606235v3
2006-11-12,Magnetic resonance spectroscopy of perpendicularly magnetized permalloy multilayer disks,"Using a Magnetic Resonance Force Microscope, we compare the ferromagnetic
resonance spectra of individual micron-size disks with identical diameter, 1
$m$m, but different layer structures. For a disk composed of a single 43.3 nm
thick permalloy (Py) layer, the lowest energy mode in the perpendicular
configuration is the uniform precession. The higher energy modes are standing
spin-waves confined along the diameter of the disk. For a Cu(30)/Py(100)/Cu(30)
nm multilayer structure, it has been interpreted that the lowest energy mode
becomes a precession localized at the Cu/Py interfaces. When the multilayer is
changed to Py(100)/Cu(10)/Py(10) nm, this localized mode of the thick layer is
coupled to the precession of the thin layer.",0611307v3
2007-04-19,Ferromagnetic resonance force microscopy on a thin permalloy film,"Ferromagnetic Resonance Force Microscopy (FMRFM) offers a means of performing
local ferromagnetic resonance. We have studied the evolution of the FMRFM force
spectra in a continuous 50 nm thick permalloy film as a function of probe-film
distance and performed numerical simulations of the intensity of the FMRFM
probe-film interaction force, accounting for the presence of the localized
strongly nonuniform magnetic field of the FMRFM probe magnet. Excellent
agreement between the experimental data and the simulation results provides
insight into the mechanism of FMR mode excitation in an FMRFM experiment.",0704.2442v1
2008-02-13,Direct observation of domain wall structures in curved permalloy wires containing an anti-notch,"The formation and field response of head-to-head domain walls in curved
permalloy wires, fabricated to contain a single anti-notch, have been
investigated using Lorentz microscopy. High spatial resolution maps of the
vector induction distribution in domain walls close to the anti-notch have been
derived and compared with micromagnetic simulations. In wires of 10 nm
thickness the walls are typically of a modified asymmetric transverse wall
type. Their response to applied fields tangential to the wire at the anti-notch
location was studied. The way the wall structure changes depends on whether the
field moves the wall away from or further into the notch. Higher fields are
needed and much more distorted wall structures are observed in the latter case,
indicating that the anti-notch acts as an energy barrier for the domain wall.",0802.1814v1
2008-12-29,Temperature dependent dynamic and static magnetic response in magnetic tunnel junctions with Permalloy layers,"Ferromagnetic resonance and static magnetic properties of CoFe/Al2O3/CoFe/Py
and CoFe/Al2O3/CoFeB/Py magnetic tunnel junctions and of 25nm thick
single-layer Permalloy(Py) films have been studied as a function of temperature
down to 2K. The temperature dependence of the ferromagnetic resonance excited
in the Py layers in magnetic tunnel junctions shows knee-like enhancement of
the resonance frequency accompanied by an anomaly in the magnetization near
60K. We attribute the anomalous static and dynamic magnetic response at low
temperatures to interface stress induced magnetic reorientation transition at
the Py interface which could be influenced by dipolar soft-hard layer coupling
through the Al2O3 barrier.",0812.4953v1
2009-03-06,Near-field interaction between domain walls in adjacent Permalloy nanowires,"The magnetostatic interaction between two oppositely charged transverse
domain walls (DWs)in adjacent Permalloy nanowires is experimentally
demonstrated. The dependence of the pinning strength on wire separation is
investigated for distances between 13 and 125 nm, and depinning fields up to 93
Oe are measured. The results can be described fully by considering the
interaction between the full complex distribution of magnetic charge within
rigid, isolated DWs. This suggests the DW internal structure is not appreciably
disturbed by the pinning potential, and that they remain rigid although the
pinning strength is significant. This work demonstrates the possibility of
non-contact DW trapping without DW perturbation and full continuous flexibility
of the pinning potential type and strength. The consequence of the interaction
on DW based data storage schemes is evaluated.",0903.1195v1
2009-11-13,Quantifying spin Hall angles from spin pumping: Experiments and Theory,"Spin Hall effects intermix spin and charge currents even in nonmagnetic
materials and, therefore, ultimately may allow the use of spin transport
without the need for ferromagnets. We show how spin Hall effects can be
quantified by integrating permalloy/normal metal (N) bilayers into a coplanar
waveguide. A dc spin current in N can be generated by spin pumping in a
controllable way by ferromagnetic resonance. The transverse dc voltage detected
along the permalloy/N has contributions from both the anisotropic
magnetoresistance (AMR) and the spin Hall effect, which can be distinguished by
their symmetries. We developed a theory that accounts for both. In this way, we
determine the spin Hall angle quantitatively for Pt, Au and Mo. This approach
can readily be adapted to any conducting material with even very small spin
Hall angles.",0911.2725v2
2010-01-14,Conductance in Co/Al2O3/Si/Al2O3 permalloy with asymmetrically doped barrier,"Permalloy magnetic tunnel junctions. Complementary low frequency noise
measurements are used to understand the conductance results. The obtained data
indicate the breakdown of the Coulomb blockade for thickness of the asymmetric
silicon layer exceeding 1.2\AA . The crossover in the conductance, the
dependence of the tunnelling magnetoresistance with the bias voltage and the
noise below 80K correspond to 1 monolayer coverage. Interestingly, the zero
bias magnetoresistance remains nearly unaffected by the presence of the silicon
layer. The proposed model uses Larkin-Matveev approximation of tunnelling
through a single impurity layer generalized to 3D and takes into account the
variation of the barrier shape with the bias voltage. The main difference is
the localization of all the impurity levels within a single atomic layer. In
the high thickness case, up to 1.8\AA, we have introduced a phenomenological
parameter, which reflects the number of single levels on the total density of
silicon atoms.",1001.2415v1
2010-05-04,Effect of disorder studied with ferromagnetic resonance for arrays of tangentially magnetized sub-micron Permalloy discs fabricated by nanosphere lithography,"Tangentially magnetized trigonal arrays of sub-micron Permalloy discs are
characterized with ferromagnetic resonance to determine the possible
contributions to frequency and linewidth from array disorder. Each array is
fabricated by a water-surface self-assembly lithographic technique, and
consists of a large trigonal array of 700 nm diameter magnetic discs. Each
array is characterized by a different degree of ordering. Two modes are present
in the ferromagnetic resonance spectra: a large amplitude, `fundamental' mode
and a lower amplitude mode at higher field. Angular dependence of the resonance
field in a very well ordered array is found to be negligible for both modes.
The relationship between resonance frequency and applied magnetic field is
found to be uncorrelated with array disorder. Linewidth is found to increase
with increasing array disorder.",1005.0452v3
2010-07-06,The dynamics of magnetic vortex states in a single permalloy nanoparticle,"We demonstrate a novel method allowing the study of the magnetic state
dynamics of a single nanoparticle by means of electron transport measurements.
Elliptical 550 nm x 240 nm permalloy nanoparticles are wired with non-magnetic
leads for magnetotransport measurements in the presence of a radio-frequency
(RF) field. Their resistance exhibits sharp jumps due to the anisotropic
magnetoresistance even at room temperature. An RF field induces DC voltage
across the nanoparticle which can be partially depleted at a certain RF
frequency when a magnetic vortex core resonance is present. An application of
an additional DC magnetic field eliminates the vortex and reinstates the
unperturbed DC voltage level. The vortex core resonance frequencies are found
and the smallest resonance widths are estimated to be less than 6 MHz.",1007.0958v1
2010-07-19,Standing spin-wave mode structure and linewidth in partially disordered perpendicularly magnetized sub-micron Permalloy disc arrays,"Standing spin wave mode frequencies and linewidths in partially disordered
perpendicular magnetized arrays of sub-micron Permalloy discs are measured
using broadband ferromagnetic resonance and compared to analytical results from
a single, isolated disc. The measured mode structure qualitatively reproduces
the structure expected from the theory. Fitted demagnetizing parameters
decrease with increasing array disorder. The frequency difference between the
first and second radial modes is found to be higher in the measured array
systems than predicted by theory for an isolated disc. The relative frequencies
between successive spin wave modes are unaffected by reduction of the
long-range ordering of discs in the array. An increase in standing spin wave
resonance linewidth at low applied magnetic fields is observed and grows more
severe with increased array disorder.",1007.3062v5
2010-08-16,Domain-wall depinning assisted by pure spin currents,"We study the depinning of domain walls by pure diffusive spin currents in a
nonlocal spin valve structure based on two ferromagnetic permalloy elements
with copper as the nonmagnetic spin conduit. The injected spin current is
absorbed by the second permalloy structure with a domain wall and from the
dependence of the wall depinning field on the spin current density we find an
efficiency of 6*10^{-14}T/(A/m^2), which is more than an order of magnitude
larger than for conventional current induced domain wall motion. Theoretically
we reproduce this high efficiency, which arises from the surface torques
exerted by the absorbed spin current that lead to efficient depinning.",1008.2773v1
2010-09-10,Permalloy-based carbon nanotube spin-valve,"In this Letter we demonstrate that Permalloy (Py), a widely used Ni/Fe alloy,
forms contacts to carbon nanotubes (CNTs) that meet the requirements for the
injection and detection of spin-polarized currents in carbon-based spintronic
devices. We establish the material quality and magnetization properties of Py
strips in the shape of suitable electrical contacts and find a sharp
magnetization switching tunable by geometry in the anisotropic
magnetoresistance (AMR) of a single strip at cryogenic temperatures. In
addition, we show that Py contacts couple strongly to CNTs, comparable to Pd
contacts, thereby forming CNT quantum dots at low temperatures. These results
form the basis for a Py-based CNT spin-valve exhibiting very sharp resistance
switchings in the tunneling magnetoresistance, which directly correspond to the
magnetization reversals in the individual contacts observed in AMR experiments.",1009.1960v1
2010-09-26,Detection and quantification of inverse spin Hall effect from spin pumping in permalloy/normal metal bilayers,"Spin pumping is a mechanism that generates spin currents from ferromagnetic
resonance (FMR) over macroscopic interfacial areas, thereby enabling sensitive
detection of the inverse spin Hall effect that transforms spin into charge
currents in non-magnetic conductors. Here we study the spin-pumping-induced
voltages due to the inverse spin Hall effect in permalloy/normal metal bilayers
integrated into coplanar waveguides for different normal metals and as a
function of angle of the applied magnetic field direction, as well as microwave
frequency and power. We find good agreement between experimental data and a
theoretical model that includes contributions from anisotropic
magnetoresistance (AMR) and inverse spin Hall effect (ISHE). The analysis
provides consistent results over a wide range of experimental conditions as
long as the precise magnetization trajectory is taken into account. The spin
Hall angles for Pt, Pd, Au and Mo were determined with high precision to be
$0.013\pm0.002$, $0.0064\pm0.001$, $0.0035\pm0.0003$ and $-0.0005\pm0.0001$,
respectively.",1009.5089v1
2010-11-01,Quantitative magnetic force microscopy on permalloy dots using an iron filled carbon nanotube probe,"We have characterized a new Magnetic Force Microscopy (MFM) probe based on an
iron filled carbon nanotube (FeCNT) using MFM imaging on permalloy (Py) disks
saturated in a high magnetic field perpendicular to the disk plane. The
experimental data are accurately modeled by describing the FeCNT probe as
having a single magnetic monopole at its tip whose effective magnetic charge is
determined by the diameter of the iron wire enclosed in the carbon nanotube and
its saturation magnetization 4 \pi M_s ~ 2.2 x 10^4 G. A magnetic monopole
probe enables quantitative measurements of the magnetic field gradient close to
the sample surface. The lateral resolution is defined by the diameter of the
iron wire ~15 nm and the probe-sample separation. As a demonstration, the
magnetic field gradients close to the surface of a Py dot in domain and vortex
states were imaged.",1011.0389v1
2011-03-02,Classification of super domains and super domain walls in permalloy antidot lattices,"We study the remanent domain configurations of rectangular permalloy antidot
lattices over a range of lattice parameters. The influence of antidot diameter,
antidot spacing, and the aspect ratio of the lattice on the remanent domain
configuration are investigated by magnetic force microscopy and supported by
micromagnetic simulations. In the remanent state, areas of cells with the same
orientation of average magnetization form magnetic super domains separated by
super domain walls (SDWs). Two types of SDWs are identified. The first type is
characterized by low stray field energy, is linear, and expands over many
lattice constants. In contrast the second type shows high stray field energy
and is situated at kinks of low energy SDWs. Its width can vary from a minimum
of two lattice cells up to several lattice constants, depending on the lattice
parameters. The occurrence and structure of these two types of SDWs as function
of lattice parameters are classified and discussed in terms of the interplay of
stray field and exchange energy.",1103.0395v2
2011-11-26,Quantum depinning of the magnetic vortex core in micron-size permalloy disks,"The vortex state, characterized by an in-plane closed flux domain structure
and an out-of-plane magnetization at its centre (the vortex core), is one of
the magnetic equilibria of thin soft ferromagnetic micron-size dots. In the
last two decades many groups have been working on the dynamics of the magnetic
moment in nanomagnetic materials at low temperatures, it giving rise to the
observation of quantum relaxations and quantum hysteresis cycles. For the first
time, we report experimental evidence of quantum dynamics of the vortex core of
micron-size permalloy (Fe$_{19}$Ni$_{81}$) disks induced by the application of
an in-plane magnetic field. It is attributed to the quantum tunneling of the
vortex core through pinning barriers, which are associated to structural
defects in the dots, towards its equilibrium position.",1111.6171v1
2012-06-08,Spin-dependent Seebeck coefficients of Ni_{80}Fe_{20} and Co in nanopillar spin valves,"We have experimentally determined the spin-dependent Seebeck coefficient of
permalloy (Ni_{80}Fe_{20}) and cobalt (Co) using nanopillar spin valve devices.
The devices were specifically designed to completely separate heat related
effects from charge related effects. A pure heat current through the nanopillar
spin valve, a stack of two ferromagnetic layers (F) separated by a non-magnetic
layer (N), leads to a thermovoltage proportional to the spin-dependent Seebeck
coefficient S_{S}=S_{\uparrow}-S_{\downarrow} of the ferromagnet, where
S_{\uparrow} and S_{\downarrow} are the Seebeck coefficient for spin-up and
spin-down electrons. By using a three-dimensional finite-element model (3D-FEM)
based on spin-dependent thermoelectric theory, whose input material parameters
were measured in separate devices, we were able to accurately determine a
spin-dependent Seebeck coefficient of -1.8 microvolt/Kelvin and -4.5
microvolt/Kelvin for cobalt and permalloy, respectively corresponding to a
Seebeck coefficient polarization P_{S}=S_{S}/S_{F} of 0.08 and 0.25, where
S_{F} is the Seebeck coefficient of the ferromagnet. The results are in
agreement with earlier theoretical work in Co/Cu multilayers and spin-dependent
Seebeck and spin-dependent Peltier measurements in Ni_{80}Fe_{20}/Cu spin valve
structures.",1206.1659v1
2012-10-09,Spectral Characteristics of the Microwave Emission by the Spin Hall Nano-Oscillator,"We utilized microwave spectroscopy to study the magnetization oscillations
locally induced in a Permalloy film by a pure spin current, which is generated
due to the spin Hall effect in an adjacent Pt layer. The oscillation frequency
is lower than the ferromagnetic resonance of Permalloy, indicating that the
oscillation forms a self-localized nonpropagating spin-wave soliton. At
cryogenic temperatures, the spectral characteristics are remarkably similar to
the traditional spin-torque nano-oscillators driven by spin-polarized currents.
However, the linewidth of the oscillation increases exponentially with
temperature and an additional peak appears in the spectrum below the
ferromagnetic resonance, suggesting that the spectral characteristics are
determined by interplay between two localized dynamical states.",1210.2758v2
2013-09-26,Proximity effect of spin orbit coupling in Pt/Co2FeAl and Pt/Permalloy bilayers_810571,"Proximity effect of spin orbit coupling is investigated through anomalous
Hall effect in Pt/Co2FeAl and Pt/Permalloy bilayers. A series of nontrivial
magnetotransport behaviors, resulting from a strong impact of phonons on skew
scattering, is observed in these films with ultrathin ferromagnetic layers. The
parameters representing skew scattering, side jump and intrinsic contributions
are dramatically enhanced when the ferromagnetic layer is very thin, and they
have clear linear dependences on the reciprocal of ferromagnetic layer
thickness, indicating a powerful influence of Pt/Ferromagnet interface. Further
study on Cu/Co2FeAl and Ta/Co2FeAl bilayers reveals that a simple interface
scattering without intense spin orbit coupling is not sufficient to trigger
such a phenomenon. The proximity effect of spin orbit coupling is thus
suggested to occur at the Pt/Ferromagnet interface, and as a result quite large
anomalous Hall angle (0.036) and Nernst angle (0.23) are confirmed in the
Pt/CFA films at room temperature.",1309.7023v1
2014-07-14,Circular single domains in hemispherical small size Permalloy clusters,"We have studied ferromagnetic Permalloy clusters obtained by
electrodeposition on n-type silicon. Magnetization measurements reveal
hysteresis loops almost independent on temperature and very similar in shape to
those obtained in nanodisks with diameter bigger than 150nm. The spin
configuration for the ground state, obtained by micromagnetic simulation, shows
topological vortices with random chirality and polarization. This behaviour in
the small diameter clusters (~80nm), is attributed to the Dzyaloshinskii-Moriya
interaction that arises in its hemispherical geometries. This magnetization
behaviour can be utilized to explain the magnetoresistance measured with
magnetic field in plane and out of sample plane.",1407.3813v2
2014-07-29,Controllable Schottky Barriers between MoS2 and Permalloy,"MoS2 is a layered two-dimensional material with strong spin-orbit coupling
and long spin lifetime, which is promising for electronic and spintronic
applications. However, because of its large band gap and small electron
affinity, a considerable Schottky barrier exists between MoS2 and contact
metal, hindering the further study of spin transport and spin injection in
MoS2. Although substantial progress has been made in improving device
performance, the existence of metal-semiconductor Schottky barrier has not yet
been fully understood. Here, we investigate permalloy (Py) contacts to both
multilayer and monolayer MoS2. Ohmic contact is developed between multilayer
MoS2 and Py electrodes with a negative Schottky barrier, which yields a high
field-effect mobility exceeding 55 cm2V-1s-1 at low temperature. Further, by
applying back gate voltage and inserting different thickness of Al2O3 layer
between the metal and monolayer MoS2, we have achieved a good tunability of the
Schottky barrier height (down to zero). These results are important in
improving the performance of MoS2 transistor devices; and it may pave the way
to realize spin transport and spin injection in MoS2.",1407.7652v2
2014-09-22,Magnetic vortex chirality switching in Permalloy nanowires with asymmetric notches,"We have investigated the motion of vortex domain walls passing across non
symmetric triangular notches in single Permalloy nanowires. We have measured
hysteresis cycles using the focused magneto-optical Kerr effect before and
beyond the notch, which allowed to probe beyond the notch the occurrence
probability of clockwise (CW) and counter-clockwise (CCW) walls in tail-to-tail
(TT) and head-to-head (HH) configurations. We present experimental evidence of
chirality flipping provided by the vortex -- notch interaction. With a low exit
angle the probability of chirality flipping increases and here with the lowest
angle of 15$^o$ the probability of propagation of the energetically favored
domain wall configuration (CCW for TT or CW for HH walls) is $\approx 75\%$.
Micromagnetic simulations reveal details of the chirality reversal dynamics.",1409.6370v2
2014-10-02,Spin wave non-reciprocity and beating in permalloy by time-resolved magneto-optical Kerr effect,"We have studied the propagation characteristics of spin wave modes in a
permalloy stripe by time-resolved magneto-optical Kerr effect techniques. We
observe a beating interference pattern in the time domain under the influence
of an electrical square pulse excitation at the center of the stripe. We also
probe the non-reciprocal behavior of propagating spin waves with a dependence
on the external magnetic field. Spatial dependence studies show that localized
edge mode spin waves have a lower frequency than spin waves in the center of
the stripe, due to the varying magnetization vector across the width of the
stripe.",1410.0441v1
2014-10-02,Strong coupling between a permalloy ferromagnetic contact and a helical edge channel in a narrow HgTe quantum well,"We experimentally investigate spin-polarized electron transport between a
permalloy ferromagnet and the edge of a two-dimensional electron system with
band inversion, realized in a narrow, 8~nm wide HgTe quantum well. In zero
magnetic field, we observe strong asymmetry of the edge potential distribution
with respect to the ferromagnetic ground lead. This result indicates, that the
helical edge channel, specific for the structures with band inversion even at
the conductive bulk, is strongly coupled to the ferromagnetic side contact,
possibly due to the effects of proximity magnetization. It allows selective and
spin-sensitive contacting of helical edge states.",1410.0585v5
2014-10-30,Intrinsic synchronization of an array of spin-torque oscillators driven by the spin-Hall effect,"This paper micromagnetically studies the magnetization dynamics driven by the
spin-Hall effect in a Platinum/Permalloy bi-layer. For a certain field and
current range, the excitation of a uniform mode, characterized by a power with
a spatial distribution in the whole ferromagnetic cross section, is observed.
We suggest to use the ferromagnet of the bi-layer as basis for the realization
of an array of spin-torque oscillators (STOs): the Permalloy ferromagnet will
act as shared free layer, whereas the spacers and the polarizers are built on
top of it. Following this strategy, the frequency of the uniform mode will be
the same for the whole device, creating an intrinsic synchronization. The
synchronization of an array of parallely connected STOs will allow to increase
the output power, as necessary for technological applications.",1410.8342v1
2014-12-29,Domain wall magneto-Seebeck effect,"The interplay between charge, spin, and heat currents in magnetic nano
systems subjected to a temperature gradient has lead to a variety of novel
effects and promising applications studied in the fast-growing field of
spincaloritronics. Here we explore the magnetothermoelectrical properties of an
individual magnetic domain wall in a permalloy nanowire. In thermal gradients
of the order of few Kelvin per micrometer along the long wire axis, we find a
clear magneto-Seebeck signature due to the presence of a single domain wall.
The observed domain wall magneto-Seebeck effect can be explained by the
magnetization-dependent Seebeck coefficient of permalloy in combination with
the local spin configuration of the domain wall.",1412.8289v1
2015-01-07,Engineering magnetic domain-wall structure in permalloy nanowires,"Using Lorentz transmission electron microscopy we investigate the behavior of
domain walls pinned at non-topographic defects in Cr(3 nm)/Permalloy(10
nm)/Cr(5 nm) nanowires of width 500 nm. The pinning sites consist of linear
defects where magnetic properties are modified by a Ga ion probe with diameter
~ 10 nm using a focused ion beam microscope. We study the detailed change of
the modified region (which is on the scale of the focused ion spot) using
electron energy loss spectroscopy and differential phase contrast imaging on an
aberration (Cs) corrected scanning transmission electron microscope. The signal
variation observed indicates that the region modified by the irradiation
corresponds to ~ 40-50 nm despite the ion probe size of only 10 nm. Employing
the Fresnel mode of Lorentz transmission electron microscopy, we show that it
is possible to control the domain wall structure and its depinning strength not
only via the irradiation dose but also the line orientation.",1501.01410v1
2015-01-30,Head-to-Head Domain Wall Structures in Wide Permalloy Strips,"We analyze the equilibrium micromagnetic domain wall structures encountered
in Permalloy strips of a wide range of thicknesses and widths, with strip
widths up to several micrometers. By performing an extensive set of
micromagnetic simulations, we show that the equilibrium phase diagram of the
domain wall structures exhibits in addition to the previously found structures
(symmetric and asymmetric transverse walls, vortex wall) also double vortex and
triple vortex domain walls for large enough strip widths and thicknesses. Also
several metastable domain wall structures are found for wide and/or thick
strips. We discuss the details of the relaxation process from random
magnetization initial states towards the stable domain wall structure, and show
that our results are robust with respect to changes of e.g. the magnitude of
the Gilbert damping constant and details of the initial conditions.",1501.07731v1
2015-05-05,Three-dimensional Character of the Magnetization Dynamics in Magnetic Vortex Structures - Hybridization of Flexure Gyromodes with Spin Waves,"Three-dimensional linear spin-wave eigenmodes of a Permalloy disk having
finite thickness are studied by micromagnetic simulations based on the
Landau-Lifshitz-Gilbert equation. The eigenmodes found in the simulations are
interpreted as linear superpositions (hybridizations) of 'approximate'
three-dimensional eigenmodes, which are the fundamental gyromode $G_0$, the
spin-wave modes and the higher-order gyromodes $G_N$ (flexure modes), the
thickness dependence of which is represented by perpendicular standing spin
waves. This hybridization leads to new and surprising dependencies of the mode
frequencies on the disk thickness. The three-dimensional character of the
eigenmodes is essential to explain the recent experimental results on
vortex-core reversal observed in relatively thick Permalloy disks.",1505.01148v2
2015-10-23,Mapping the domain wall pinning landscape in ferromagnetic films,"The propagation of domain walls in a ferromagnetic film is largely determined
by domain wall pinning at defects in the material. In this letter we map the
effective potential landscape for domain wall pinning in Permalloy films by
raster scanning a single ferromagnetic vortex and monitoring the hysteretic
vortex displacement vs. applied magnetic field. The measurement is carried out
using a differential magneto-optical microscopy technique which yields spatial
sensitivity $\sim 10$ nm. We present a simple algorithm for extracting an
effective pinning potential from the measurement of vortex displacement vs.
applied field. The resulting maps of the pinning potential reveal distinct
types of pinning sites, which we attribute to quasi-zero-, one-, and
two-dimensional defects in the Permalloy film.",1510.07059v2
2015-11-30,Frequency non-reciprocity of surface spin wave in Permalloy thin films,"Surface spin waves in thin Permalloy films are studied by means of
propagative spin wave spectroscopy. We observe a systematic difference of up to
several tens of MHz when comparing the frequencies of counter-propagating
waves. This frequency non-reciprocity effect is modeled using an analytical
dipole-exchange theory that considers the mutual influence of non-reciprocal
spin wave modal profiles and differences in magnetic anisotropies at the two
film surfaces. At moderate film thickness (20 nm and below), the frequency
non-reciprocity scales linearly with the wave vector and quadratically with the
thickness, whereas a more complex non-monotonic behavior is observed at larger
thickness. Our work suggests that surface wave frequency non-reciprocity can be
used as an accurate spectroscopic probe of magnetic asymmetries in thin
ferromagnetic films.",1511.09351v1
2015-12-04,Current and field stimulated motion of domain wall in narrow permalloy stripe,"Of the new types of cryoelectronic devices under development, including phase
shifters, giant magnetoresistance switches, diodes, transistors, and memory
cells, some are based on hybrid superconductor-normal metal or
superconductor-ferromagnet films. Control of these devices is realized by means
of pulses of voltage, light, or magnetic field. Spin-polarized current may be
used to switch low-temperature devices, as in spin-electronic devices. In the
superconducting layer, the current is dissipation less, which would bring large
reduction of energy consumption. We demonstrate that mag-netic domain walls in
bilayer niobium-permalloy stripes are shifted by electrical current along the
stripe even at low tem-perature, with the niobium in the superconducting state.
The wall motion in response to current pulses is quite different from that
induced by a magnetic field pulses only. The effect could be used to create a
new type of sequentially switched serial devices because of very high value of
the wall velocity, which excides by many orders of magnitude the velocity of
the wall moved with magnetic field pulses.",1512.01372v1
2016-02-23,Experimental Investigation of Temperature-Dependent Gilbert Damping in Permalloy Thin Films,"The Gilbert damping of ferromagnetic materials is arguably the most important
but least understood phenomenological parameter that dictates real-time
magnetization dynamics. Understanding the physical origin of the Gilbert
damping is highly relevant to developing future fast switching spintronics
devices such as magnetic sensors and magnetic random access memory. Here, we
report an experimental study of temperature-dependent Gilbert damping in
permalloy (Py) thin films of varying thicknesses by ferromagnetic resonance.
From the thickness dependence, two independent contributions to the Gilbert
damping are identified, namely bulk damping and surface damping. Of particular
interest, bulk damping decreases monotonically as the temperature decreases,
while surface damping shows an enhancement peak at the temperature of ~50 K.
These results provide an important insight to the physical origin of the
Gilbert damping in ultrathin magnetic films.",1602.07325v1
2016-05-19,Magnetic Domain Wall Engineering in a Nanoscale Permalloy Junction,"Nanoscale magnetic junction provides a useful approach to act as the building
block for magnetoresistive random access memories (MRAM), where one of the key
issues is to control the magnetic domain configuration. Here, we study the
domain structure and the magnetic switching in the Permalloy (Fe20Ni80)
nanoscale magnetic junctions with different thicknesses by using micromagnetic
simulations. It is found that both the 90-degree and 45-degree domain walls can
be formed between the junctions and the wire arms depending on the thickness of
the device. The magnetic switching fields show distinct thickness dependencies
with a broad peak varying from 7 nm to 22 nm depending on the junction sizes,
and the large magnetic switching fields favor the stability of the MRAM
operation.",1605.05998v2
2016-08-04,Emergence of the stripe-domain phase in patterned Permalloy films,"The occurrence of stripe domains in ferromagnetic Permalloy
(Py=Fe$_{20}$Ni$_{80}$) is a well known phenomenon which has been extensively
observed and characterized. This peculiar magnetic configuration appears only
in films with a thickness above a critical value ($d_{cr}$), which is strongly
determined by the sputtering conditions (i.e. deposition rate, temperature,
magnetic field). So far, $d_{cr}$ has usually been presented as the boundary
between the homogeneous (H) and stripe-domains (SD) regime, respectively below
and above $d_{cr}$. In this work we study the transition from the H to the SD
regime in thin films and microstructured bridges of Py with different
thicknesses. We find there is an intermediate regime, over a quite significant
thickness range below d$_{cr}$, which is signaled in confined structures by a
quickly changing domain-wall configuration and by a broadening of the
magnetoresistance dip at the coercive field. We call this the emerging
stripe-domains (ESD) regime. The transition from the ESD to the SD regime is
accompanied by a sharp increase of the magnetoresistance ratio at the thickness
where stripes appear in MFM.",1608.01527v1
2016-09-05,Coarsening dynamics of topological defects in thin Permalloy films,"We study the dynamics of topological defects in the magnetic texture of
rectangular Permalloy thin film elements during relaxation from random
magnetization initial states. Our full micromagnetic simulations reveal complex
defect dynamics during relaxation towards the stable Landau closure domain
pattern, manifested as temporal power-law decay, with a system-size dependent
cut-off time, of various quantities. These include the energy density of the
system, and the number densities of the different kinds of topological defects
present in the system. The related power-law exponents assume non-trivial
values, and are found to be different for the different defect types. The
exponents are robust against a moderate increase in the Gilbert damping
constant and introduction of quenched structural disorder. We discuss details
of the processes allowed by conservation of the winding number of the defects,
underlying their complex coarsening dynamics.",1609.01094v1
2017-08-05,Spin Injection and Detection via the Anomalous Spin Hall Effect in a Ferromagnetic Metal,"We report a novel spin injection and detection mechanism via the anomalous
Hall effect in a ferromagnetic metal. The anomalous spin Hall effect (ASHE)
refers to the transverse spin current generated within the ferromagnet. We
utilize the ASHE and its reciprocal effect to electrically inject and detect
magnons in a magnetic insulator in a non-local geometry. Our experiments reveal
that permalloy can have a higher spin injection and detection efficiency to
that of platinum, owing to the ASHE. We also demonstrate the tunability of the
ASHE via the orientation of the permalloy magnetization, thus creating new
possibilities for spintronic applications.",1708.01752v1
2017-12-11,Quantitative magneto-optical investigation of superconductor/ferromagnet hybrid structures,"We present a detailed quantitative magneto-optical imaging study of several
superconductor/ferromagnet hybrid structures, including Nb deposited on top of
thermomagnetically patterned NdFeB, and permalloy/niobium with erasable and
tailored magnetic landscapes imprinted in the permalloy layer. The
magneto-optical imaging data is complemented with and compared to scanning Hall
probe microscopy measurements. Comprehensive protocols have been developed for
calibrating, testing, and converting Faraday rotation data to magnetic field
maps. Applied to the acquired data, they reveal the comparatively weaker
magnetic response of the superconductor from the background of larger fields
and field gradients generated by the magnetic layer.",1712.03723v2
2018-05-29,Efficient injection and detection of out-of-plane spins via the anomalous spin Hall effect in permalloy nanowires,"We report a novel mechanism for the electrical injection and detection of
out-of-plane spin accumulation via the anomalous spin Hall effect (ASHE), where
the direction of the spin accumulation can be controlled by manipulating the
magnetization of the ferromagnet. This mechanism is distinct from the spin Hall
effect (SHE), where the spin accumulation is created along a fixed direction
parallel to an interface. We demonstrate this unique property of the ASHE in
nanowires made of permalloy (Py), to inject and detect out-of-plane spin
accumulation in a magnetic insulator, yttrium iron garnet (YIG). We show that
the efficiency for the injection/detection of out-of-plane spins can be up to
50% of that of in-plane spins. We further report the possibility to detect spin
currents parallel to the Py/YIG interface for spins fully oriented in the
out-of-plane direction, resulting in a sign reversal of the non-local magnon
spin signal. The new mechanisms that we have demonstrated are highly relevant
for spin torque devices and applications.",1805.11575v1
2018-11-25,Temperature-Dependent Magnetization Reversal in Exchange Bias NiFe/IrMn/NiFe Structures,"We demonstrate the magnetization reversal features in NiFe/IrMn/NiFe
thin-film structures with 40% and 75% relative content of Ni in Permalloy in
the temperature range from 80 K to 300 K. At the descending branches of the
hysteresis loops, the magnetization reversal sequence of the two ferromagnetic
layers is found to depend on the type of NiFe alloy. In the samples with 75%
relative content of Ni, the bottom ferromagnetic layer reverses prior to the
top one. On the contrary, in the samples with 40% of Ni, the top ferromagnetic
layer reverses prior to the bottom one. These tendencies of magnetization
reversal are preserved in the entire range of temperatures. These distinctions
can be explained by the morphological and structural differences of interfaces
in the samples based on two types of Permalloy.",1811.09963v1
2019-11-19,Imaging non-standing spin-waves in confined micron-sized ferromagnetic structures under uniform excitation,"A non-standing character of directly imaged spin-waves in confined
micron-sized ultrathin permalloy (Ni\textsubscript{80}Fe\textsubscript{20})
structures is reported along with evidence of the possibility to alter the
observed state by modifications to the sample geometry. Using micromagnetic
simulations the presence of the spin-wave modes excited in the permalloy
stripes along with the quasi-uniform modes were calculated. The predicted
spin-waves were imaged in direct space using time resolved scanning
transmission X-ray microscopy, combined with a ferromagnetic resonance
excitation scheme (STXM-FMR). STXM-FMR measurements revealed a non-standing
character of the spin-waves. Also it was shown by micromagnetic simulations and
confirmed with STXM-FMR results that the observed character of the spin-waves
can be influenced by the local magnetic fields in different sample geometries.",1911.08281v1
2018-07-16,Magnetic freezing transition in a CoO/Permalloy bilayer revealed by transverse ac susceptibility,"We utilize variable-temperature, variable-frequency magneto-optical
transverse magnetic susceptibility technique to study the static and dynamical
magnetic properties of a thin-film CoO/Permalloy bilayer. Our measurements
demonstrate that in the studied system, the directional asymmetry of the
hysteresis loop is associated mainly with the difference in the reversal
mechanisms between the two reversed states of magnetization stabilized by the
exchange-induced uniaxial anisotropy. The latter is found to be much larger
than the exchange-induced unidirectional anisotropy of the ferromagnet. We also
observe an abrupt variation of the frequency-dependent imaginary part of ac
susceptibility near the exchange bias blocking temperature, consistent with the
magnetic freezing transition inferred from the previous time-domain studies of
magnetic aging in similar systems. The developed measurement approach enables
precise characterization of the dynamical and static characteristics of
thin-film magnetic heterostructures that can find applications in
reconfigurable magnonic and neuromorphic circuits.",1807.05990v2
2018-02-13,Micromagnetic evaluation of the dissipated heat in cylindrical magnetic nanowires,"Magnetic nanowires (NW) are promising candidates for heat generation under
AC-field application due to their large shape anisotropy. They may be used for
catalysis, hyperthermia or water purification treatments. In the present work
we theoretically evaluate the heat dissipated by a single magnetic nanowire,
originated from the domain wall dynamics under the action of an AC-field. We
compare the Permalloy NWs (which demagnetize via the transverse wall
propagation) with the Co fcc NWs whose reversal mode is via a vortex domain
wall. The average hysteresis loop areas -which are proportional to the Specific
Absorption Rate (SAR)- as a function of the field frequency have a pronounced
maximum in the range 200MHz-1GHz. This maximum frequency is smaller in
Permalloy than in Co and depends on the nanowire length. A simple model related
to the nucleation and propagation time and domain wall velocity (higher for the
vortex than for the transverse domain wall) is proposed to explain the
non-monotonic SAR dependence on the frequency.",1802.04709v1
2018-02-18,Scaling of nonlinear susceptibilities in artificial permalloy honeycomb lattice,"Two-dimensional artificial magnetic honeycomb lattice is predicted to
manifest thermodynamic phase transition to the spin solid order ground state at
low temperature. Nonlinear susceptibilities are very sensitive to thermodynamic
phase transition. We have performed the analysis of nonlinear susceptibility to
explore the thermodynamic nature of spin solid phase transition in artificial
honeycomb lattice of ultra-small connected permalloy (Ni$_{0.81}$Fe$_{0.19}$)
elements, typical length of $\simeq$ 12 nm. The nonlinear susceptibility,
$\chi_{n1}$, is found to exhibit an unusual cross-over character in both
temperature and magnetic field. The higher order susceptibility $\chi_3$
changes from positive to negative as the system traverses through the spin
solid phase transition at $T_s$ = 29 K. Additionally, the static critical
exponents, used to test the scaling of $\chi_{n1}$, do not follow the
conventional scaling relation. We conclude that the transition to the ground
state is not truly thermodynamic, thus raises doubt about the validity of
predicted zero entropy state in the spin solid phase.",1802.06325v1
2016-03-17,Spin wave amplification using the spin Hall effect in permalloy/platinum bilayers,"We investigate the effect of an electrical current on the attenuation length
of a 900 nm wavelength spin-wave in a permalloy/Pt bilayer using propagating
spin-wave spectroscopy. The modification of the spin-wave relaxation rate is
linear in current density, reaching up to 14% for a current density of
2.3$\times10^{11} $A/m$^2$ in Pt. This change is attributed to the spin
transfer torque induced by the spin Hall effect and corresponds to an effective
spin Hall angle of 0.13, which is among the highest values reported so far. The
spin Hall effect thus appears as an efficient way of amplifying/attenuating
propagating spin waves.",1603.05478v1
2017-02-09,Long-range proximity effect in Nb-based heterostructures induced by a magnetically inhomogeneous permalloy layer,"Odd-frequency triplet Cooper pairs are believed to be the carriers of
long-range superconducting correlations in ferromagnets. Such triplet pairs are
generated by inhomogeneous magnetism at the interface between a superconductor
(S) and a ferromagnet (F). So far, reproducible long-range effects were
reported only in complex layered structures designed to provide the magnetic
inhomogeneity. Here we show that spin triplet pair formation can be found in
simple unstructured Nb/Permalloy (Py = Ni_0.8Fe_0.2)/Nb trilayers and Nb/Py
bilayers, but only when the thickness of the ferromagnetic layer ranges between
140 and 250 nm. The effect is related to the emergence of an intrinsically
inhomogeneous magnetic state, which is a precursor of the well-known stripe
regime in Py that in our samples sets in at thickness larger than 300 nm.",1702.02765v1
2017-02-10,"Relative weight of the inverse spin Hall and spin rectification effects for metallic Py,Fe/Pt and insulating YIG/Pt bilayers estimated by angular dependent spin pumping measurements","We quantify the relative weight of inverse spin Hall and spin rectification
effects occurring in RF-sputtered polycrystalline permalloy, molecular beam
epitaxy-grown epitaxial iron and liquid phase epitaxy-grown yttrium-iron-garnet
bilayer systems with different capping materials. To distinguish the spin
rectification signal from the inverse spin Hall voltage the external magnetic
field is rotated in-plane to take advantage of the different angular
dependencies of the prevailing effects. We prove that in permalloy anisotropic
magnetoresistance is the dominant source for spin rectification while in
epitaxial iron the anomalous Hall effect has an also comparable strength. The
rectification in yttrium-iron-garnet/platinum bilayers reveals an angular
dependence imitating the one seen for anisotropic magnetoresistance caused by
spin Hall magnetoresistance.",1702.03119v1
2017-06-10,Spin wave nonreciprocity and magnonic band structure in thin permalloy film induced by dynamical coupling with an array of Ni stripes,"An efficient way for the control of spin wave propagation in a magnetic
medium is the use of periodic patterns known as magnonic crystals (MCs).
However, the fabrication of MCs especially bi-components, with periodicity on
nanoscale, is a challenging task due to the requirement for sharp interfaces.
An alternative method to circumvent this problem is to use homogeneous
ferromagnetic film with modified periodically surrounding. The structure is
also suitable for exploiting nonreciprocal properties of the surface spin
waves. In this work, we demonstrate that the magnonic band structure forms in
thin permalloy film due to dynamical magnetostatic coupling with Ni stripes
near its surface. We show, that the band gap width can be systematically tuned
by the changing interlayer thickness between film and stripes. We show also the
effect of nonreciprocity, which is seen at the band gap edge shifted from the
Brillouin zone boundary and also in nonreciprocal interaction of propagating
spin waves in Py film with the standing spin waves in Ni stripes. Our findings
open possibility for further investigation and exploitation of the
nonreciprocity and band structure in magnonic devices.",1706.03202v1
2017-10-03,Synchronous magnetic control of water droplets in bulk ferrofluid,"We present a microfluidic platform for two-dimensional manipulation of water
droplets immersed in bulk oil-based ferrofluid. Although non-magnetic, the
droplets are exclusively controlled by magnetic fields, without any
pressure-driven flow. The diphasic fluid layer is trapped in a submillimeter
Hele-Shaw chamber that includes permalloy tracks on its substrate. An in-plane
rotating magnetic field magnetizes the permalloy tracks, thus producing local
magnetic gradients, while an orthogonal magnetic field magnetizes the bulk
ferrofluid. To minimize the magnetostatic energy of the system, droplets are
attracted towards the locations of the tracks where ferrofluid is repelled.
Using this technique, we demonstrate synchronous generation and propagation of
water droplets, analyze PIV data of the bulk ferrofluid flow and study the
kinematics of propagation. In addition, we show controlled break-up of droplets
and droplet-to-droplet interactions. Finally, we discuss future applications
owing to the potential biocompatibility of the droplets.",1710.00961v2
2019-03-13,Spin wave stiffness and exchange stiffness of doped permalloy via ab-initio calculation,"The way doping affects the spin wave stiffness and the exchange stiffness of
permalloy (Py) is investigated via ab-initio calculations, using the
Korringa-Kohn-Rostoker (KKR) Green function formalism. By considering various
types of dopants of different nature (V, Gd, and Pt), we are able to draw
general conclusions. To describe the trends of the stiffness with doping is it
sufficient to account for the exchange coupling between nearest neighbors. The
polarizability of the impurities is not an important factor for the spin wave
stiffness. Rather, the decisive factor is the hybridization between the
impurity and the host states as reflected by changes in the Bloch spectral
function. Our theoretical results agree well with earlier experiments.",1903.05506v2
2019-03-19,Study of magnetization reversal in Neel and Bloch regime of Ni and Py stripes using Kerr microscopy,"We present a systematic study of the magnetization reversal of nickel and
permalloy micro-stripes with Neel and Bloch domain walls using Kerr microscopy.
Magnetic field driven domain propagation was observed from higher width to
lower width stripes for magnetic fields applied along the length of
micro-stripes. Stripe like domains were observed with nucleation starting in
lower width region followed by their propagation to higher width regions for
magnetic fields applied along the width of micro-stripes. The comparison of
magnetization reversal in Bloch and N\'eel domain wall regime showed higher
domain wall density in Bloch regime for both nickel and permalloy stripes.",1903.08106v3
2020-02-29,Nonreciprocal Emergence of Hybridized Magnons in magnetic thin Films,"We investigate the transfer and control of nonreciprocity through magnons
themselves in permalloy thin films deposited on surface oxide silicon
substrate. Evidences of nonreciprocal emergence of hybridized dipole exchange
magnons (spin waves) at two permalloy surfaces are provided by studying magnon
transmission and asymmetry, via Brillouin light scattering measurements. The
dipole dominated spin wave and exchange dominated spin wave are found to be
localized near the top and bottom surfaces, respectively, and traveling along
opposite directions. The nonreciprocity and the localization are intertwined
and ca n be tuned by an in plane magnetic field. The effects are well explained
by the magnetostatic theory and can be quantitatively reproduced by the
micromagnetic simulations. Our findings provide a simple and flexible approach
to nonreciprocal all magnon logi c devices with highly compatible with silicon
based integrated circuit technology.",2003.00230v4
2003-12-18,Optimization of nanostructured permalloy electrodes for a lateral hybrid spin-valve structure,"Ferromagnetic electrodes of a lateral semiconductor-based spin-valve
structure are designed to provide a maximum of spin-polarized injection
current. A single-domain state in remanence is a prerequisite obtained by
nanostructuring Permalloy thin film electrodes. Three regimes of aspect ratios
$m$ are identified by room temperature magnetic force microscopy: (i)
high-aspect ratios of $m \ge 20$ provide the favored remanent single-domain
magnetization states, (ii) medium-aspect ratios $m \sim 3$ to $m \sim 20$ yield
highly remanent states with closure domains and (iii) low-aspect ratios of $m
\le 3$ lead to multi-domain structures. Lateral kinks, introduced to bridge the
gap between micro- and macroscale, disturb the uniform magnetization of
electrodes with high- and medium-aspect ratios. However, vertical flanks help
to maintain a uniformly magnetized state at the ferromagnet-semiconcuctor
contact by domain wall pinning.",0312466v2
2017-01-20,Fast vortex wall motion in wide Permalloy strips from double switching of the vortex core,"We study vortex domain wall dynamics in wide Permalloy strips driven by
applied magnetic fields and spin-polarized electric currents. As recently
reported [V. Est\'evez and L. Laurson, Phys. Rev. B, 93, 064403 (2016)], for
sufficiently wide strips and above a threshold field, periodic dynamics of the
vortex core are localized in the vicinity of one of the strip edges, and the
velocity drop typically observed for narrow strips is replaced by a
high-velocity plateau. Here, we analyze this behavior in more detail by means
of micromagnetic simulations. We show that the high-velocity plateau originates
from a repeated double switching of the magnetic vortex core, underlying the
periodic vortex core dynamics in the vicinity of the strip edge, i.e., the
""attraction-repulsion"" effect. We also discuss the corresponding dynamics
driven by spin-polarized currents, as well as the effect of including quenched
random structural disorder to the system.",1701.05732v2
2019-08-23,Massively parallel atomistic simulation of ultrafast thermal spin dynamics of a permalloy vortex,"Ultrafast magnetization dynamics probes the most fundamental properties of
magnetic materials, exploring questions about the fundamental interactions
responsible for magnetic phenomena. Thermal effects are known to be extremely
important for laser-induced dynamics in metallic systems, but the dynamics of
topological magnetic structures are little understood. Here we apply a
massively parallel atomistic spin dynamics simulation to study the response of
a permalloy vortex to a 50 fs laser pulse. We find that macroscopically the
short timescale dynamics are indistinguishable from the bulk, but that strong
edge spin waves lead to a complex time evolution of the magnetic structure and
long-lived oscillations on the nanosecond timescale. In the near future such
simulations will provide unprecedented insight into the dynamics of magnetic
materials and devices beyond the approximations of continuum micromagnetics.",1908.08885v1
2019-09-13,Transport properties of doped permalloy via ab-initio calculations: effect of the host disorder,"Transport properties of permalloy doped with V, Co, Pt, and Au are explored
via ab-initio calculations. The Kubo-Bastin formula is evaluated within the
fully relativistic Korringa-Kohn-Rostoker Green function formalism. Finite
temperature effects are treated by means of the alloy analogy model. It is
shown that the fact that the host is disordered and not crystalline has a
profound effect on how the conductivities characterizing the anomalous Hall
effect and the spin Hall effect depend on the dopant concentration. Several
relationships between quantities characterizing charge and spin transport are
highlighted. The decrease of the longitudinal charge conductivity with
increasing doping depends on the dopant type, following the sequence
Co-Au-Pt-V. The dependence of the anomalous Hall and spin Hall conductivities
on the dopant concentration is found to be non-monotonic. Introducing a finite
temperature changes the overall trends significantly. The theoretical results
are compared with available experimental data.",1909.06066v3
2019-09-27,Thermally driven two-magnet nano-oscillator with large spin-charge conversion,"Next-generation spintronic applications require material properties that can
be hardly met by one material candidate. Here we demonstrate that by combining
insulating and metallic magnets, enhanced spin-charge conversion and
energy-efficient thermal spin currents can be realized. We develop a nanowire
device consisting of an yttrium iron garnet and permalloy bi-layer. An
interfacial temperature gradient drives the nanowire magnetization into
auto-oscillations at gigahertz frequencies. Interfacial spin coupling and
magnetoresistance of the permalloy layer translate spin dynamics into sizable
microwave signals. The results show prospect for energy-efficient spintronic
devices and present an experimental realization of magnon condensation in a
heterogeneous magnetic system.",1909.12445v1
2019-10-19,Current-induced spin-orbit field in permalloy interfaced with ultrathin Ti and Cu,"How spin-orbit torques emerge from materials with weak spin-orbit coupling
(e.g., light metals) is an open question in spintronics. Here, we report on a
field-like spin-orbit torque (i.e., in-plane spin-orbit field transverse to the
current axis) in SiO$_2$-sandwiched permalloy (Py), with the top Py-SiO$_2$
interface incorporating ultrathin Ti or Cu. In both SiO$_2$/Py/Ti/SiO$_2$ and
SiO$_2$/Py/Cu/SiO$_2$, this spin-orbit field opposes the classical Oersted
field. While the magnitude of the spin-orbit field is at least a factor of 3
greater than the Oersted field, we do not observe evidence for a significant
damping-like torque in SiO$_2$/Py/Ti/SiO$_2$ or SiO$_2$/Py/Cu/SiO$_2$. Our
findings point to contributions from a Rashba-Edelstein effect or spin-orbit
precession at the (Ti, Cu)-inserted interface.",1910.08669v2
2019-12-31,Probing magnon-magnon coupling in exchange coupled Y$_3$Fe$_5$O$_{12}$/Permalloy bilayers with magneto-optical effects,"We demonstrate the magnetically-induced transparency (MIT) effect in
Y$_3$Fe$_5$O$_{12}$(YIG)/Permalloy(Py) coupled bilayers. The measurement is
achieved via a heterodyne detection of the coupled magnetization dynamics using
a single wavelength that probes the magneto-optical Kerr and Faraday effects of
Py and YIG, respectively. Clear features of the MIT effect are evident from the
deeply modulated ferromagnetic resonance of Py due to the
perpendicular-standing-spin-wave of YIG. We develop a phenomenological model
that nicely reproduces the experimental results including the induced amplitude
and phase evolution caused by the magnon-magnon coupling. Our work offers a new
route towards studying phase-resolved spin dynamics and hybrid magnonic
systems.",1912.13407v2
2020-05-15,Direct imaging of the ac component of the pumped spin polarization with element specificity,"Spin pumping in a ferromagnet/nonferromagnet heterostructure is directly
imaged with spatial resolution as well as element selectivity. The
time-resolved detection in scanning transmission x-ray microscopy allows to
directly probe the spatial extent of the ac spin polarization in Co-doped ZnO
which is generated by spin pumping from an adjacent permalloy microstrip.
Comparing the relative phases of the dynamic magnetization component of the two
constituents is possible and found to be antiphase. The correlation between the
distribution of the magnetic excitation in the permalloy and the Co-doped ZnO
reveals that laterally there is no one-to-one correlation. The observed
distribution is rather complex, but integrating over larger areas clearly
demonstrates that the spin polarization in the nonferromagnet extends laterally
beyond the region of the ferromagnetic microstrip. Therefore the observations
are better explained by a local spin pumping efficieny and a lateral
propagation of the ac spin polarization in the nonferromagnet over the range of
a few micrometers.",2005.08728v1
2020-07-30,Resonant subwavelength control of the phase of spin waves reflected from a ferromagnetic film edge,"Using frequency-domain finite element calculations cross-checked with
micromagnetic simulations, we demonstrate that the phase of spin waves
reflected from an interface between a permalloy film and a bilayer can be
controlled by changing dimensions of the bilayer. Treating the bilayer formed
by the permalloy film and a ferromagnetic stripe as a segment of a multi-mode
waveguide, we show that spin-wave Fabry-Perot resonances of one of its modes
are responsible for the high sensitivity of the phase of reflected waves to
stripe width and the stripe-film separation. Thus, the system is a unique
realization of a fully magnonic Gires-Tournois interferometer based on a
two-modes resonator, which can be treated as a magnonic counterpart of a
metasurface, since it enables manipulation of the phase of spin waves at
subwavelength distances. Knowledge gained from these calculations might be used
to design magnonic devices such as flat lenses or magnetic particle detectors.",2007.15226v5
2020-10-09,Inplane spin orbit torque magnetization switching and its detection using the spin rectification effect at sub-GHz frequencies,"Inplane magnetization reversal of a permalloy/platinum bilayer was detected
using the spin rectification effect. Using a sub GHz microwave frequency to
excite spin torque ferromagnetic resonance (ST FMR) in the bilayer induces two
discrete DC voltages around an external static magnetic field of 0 mT. These
discrete voltages depend on the magnetization directions of the permalloy and
enable detection of the inplane magnetization reversal. The threshold current
density for the magnetization reversal is from 10 to 20 MA/cm^2, the same order
as for known spin orbit torque (SOT) switching with in-plane magnetization
materials. The magnitude of the signal is the same or larger than that of the
typical ST FMR signal; that is, detection of magnetization switching is highly
sensitive in spite of deviation from the optimal ST-FMR condition. The proposed
method is applicable to a simple device structure even for a small
ferromagnetic electrode with a width of 100 nm.",2010.04435v1
2021-06-18,Exchange bias without directional anisotropy in Permalloy/CoO bilayers,"We utilize transverse ac susceptibility measurements to characterize magnetic
anisotropy in archetypal exchange-bias bilayers of ferromagnet Permalloy (Py)
and antiferromagnet CoO. Unidirectional anisotropy is observed for thin Py, but
becomes negligible at larger Py thicknesses, even though the directional
asymmetry of the magnetic hysteresis loop remains significant. Additional
magnetoelectronic measurements, magneto-optical imaging, as well as
micromagnetic simulations show that these surprising behaviors are likely
associated with asymmetry of spin flop distribution created in CoO during Py
magnetization reversal, which facilitates the rotation of the latter back into
its field-cooled direction. Our findings suggest new possibilities for
efficient realization of multistable nanomagnetic systems for neuromorphic
applications.",2106.09924v1
2021-11-09,Design of soft magnetic materials,"We present a strategy for the design of ferromagnetic materials with
exceptionally low magnetic hysteresis, quantified by coercivity. In this
strategy, we use a micromagnetic algorithm that we have developed in previous
research and which has been validated by its success in solving the ""Permalloy
Problem"" -- the well-known difficulty of predicting the composition 78.5% Ni of
lowest coercivity in the Fe-Ni system -- and by the insight, it provides into
the ""Coercivity Paradox"" of W. F. Brown. Unexpectedly, the design strategy
predicts that cubic materials with large saturation magnetization $m_s$ and
large magnetocrystalline anisotropy constant $\kappa_1$ will have low
coercivity on the order of that of Permalloy, as long as the magnetostriction
constants $\lambda_{100}, \lambda_{111}$ are tuned to special values. The
explicit prediction for a cubic material with low coercivity is the
dimensionless number $(c_{11}-c_{12}) \lambda_{100}^2/\kappa_1 = 81$ for
$\langle 100 \rangle$ easy axes. The results would seem to have a broad
potential application, especially to magnetic materials of interest in energy
research.",2111.05456v1
2022-10-06,Field and temperature tuning of magnetic diode in permalloy honeycomb lattice,"The observation of magnetic diode behavior with ultra-low forward voltage of
5 mV renders new venue for energetically efficient spintronic device research
in the unconventional system of two-dimensional permalloy honeycomb lattice.
Detailed understanding of temperature and magnetic field tuning of diode
behavior is imperative to any practical application. Here, we report a
comprehensive study in this regard by performing electrical measurements on
magnetic diode sample as functions of temperature and magnetic field. Magnetic
diode is found to persist across the broad temperature range. Magnetic field
application unveils a peculiar reentrant characteristic where diode behavior is
suppressed in remnant field but reappears after warming to room temperature.
Analysis of I-V data suggests a modest energy gap, 0.03-0.1 eV, which is
comparable to magnetic Coulomb's interaction energy between emergent magnetic
charges on honeycomb vertices in the reverse biased state. It affirms the role
of magnetic charge correlation in unidirectional conduction in 2D honeycomb
lattice. The experimental results are expected to pave way for the utilization
of magnetic diode in next generation spintronic device applications.",2210.03184v1
2023-01-21,"Soft X-ray spectro-ptychography on boron nitride nanotubes, carbon nanotubes and permalloy nanorods","Spectro-ptychography offers improved spatial resolution and additional phase
spectral information relative to that provided by scanning transmission X-ray
microscopes (STXM). However, carrying out ptychography at the lower range of
soft X-ray energies (e.g., below 200 eV to 600 eV) on samples with weakly
scattering signals can be challenging. We present soft X-ray ptychography
results at energies as low as 180 eV and illustrate the capabilities with
results from permalloy nanorods (Fe 2p), carbon nanotubes (C 1s), and boron
nitride bamboo nanostructures (B 1s, N1s). We describe optimization of low
energy X-ray spectro-ptychography and discuss important challenges associated
with measurement approaches, reconstruction algorithms, and their effects on
the reconstructed images. A method for evaluating the increase in radiation
dose when using overlapping sampling is presented.",2301.08982v1
2023-07-18,Ultrafast spin-to-charge conversions of antiferromagnetic (111)-oriented $\mathrm{L1_2}$-$\mathrm{Mn_3Ir}$,"Antiferromagnetic $\mathrm{L1_2}$-$\mathrm{Mn_3Ir}$ combines outstanding
spin-transport properties with magnons in the terahertz (THz) frequency range.
However, the THz radiation emitted by ultrafast spin-to-charge conversion via
the inverse spin Hall effect remains unexplored. In this study, we measured the
THz emission and transmission of a permalloy/(111)-oriented
$\mathrm{L1_2}$-$\mathrm{Mn_3Ir}$ multilayer by THz time-domain spectroscopy.
The spin Hall angle was determined to be approximately constant at 0.035 within
a frequency range of 0.3-2.2 THz, in comparison with the THz spectroscopy of a
permalloy/Pt multilayer. Our results not only demonstrate the potential of
$\mathrm{L1_2}$-$\mathrm{Mn_3Ir}$ as a spintronic THz emitter but also provide
insights into the THz spin transport properties of
$\mathrm{L1_2}$-$\mathrm{Mn_3Ir}$.",2307.08928v3
2024-02-22,Unraveling the origin of antiferromagnetic coupling at YIG/permalloy interface,"We investigate the structural and electronic origin of antiferromagnetic
coupling in the Yttrium iron garnet (YIG) and permalloy (Py) bilayer system at
the atomic level. Ferromagnetic Resonance (FMR) reveal unique hybrid modes in
samples prepared with surface ion milling, indicative of antiferromagnetic
exchange coupling at the YIG/Py interface. Using scanning transmission electron
microscopy (STEM), we highlight significant interfacial differences introduced
by ion-milling. The observations suggests that the antiferromagnetic coupling
in YIG/Py bilayers is predominantly driven by an oxygen-mediated super-exchange
coupling mechanism on the tetrahedral Fe terminated YIG surface, which is
supported by density functional theory (DFT) calculations. This research
provides critical insight into the fundamental mechanisms governing the
efficiency of coupling in magnetic bilayers and underscores the pivotal role of
oxide surface termination in modulating magnetic interfacial dynamics.",2402.14553v2
2021-07-22,Interfacial Spin-Orbit Torques and Magnetic Anisotropy in WSe$_{2}$/Permalloy Bilayers,"Transition metal dichalcogenides (TMDs) are promising materials for efficient
generation of current-induced spin-orbit torques on an adjacent ferromagnetic
layer. Numerous effects, both interfacial and bulk, have been put forward to
explain the different torques previously observed. Thus far, however, there is
no clear consensus on the microscopic origin underlying the spin-orbit torques
observed in these TMD/ferromagnet bilayers. To shine light on the microscopic
mechanisms at play, here we perform thickness dependent spin-orbit torque
measurements on the semiconducting WSe$_{2}$/permalloy bilayer with various
WSe$_{2}$ layer thickness, down to the monolayer limit. We observe a large
out-of-plane field-like torque with spin-torque conductivities up to
$1\times10^4 ({\hbar}/2e) ({\Omega}m)^{-1}$. For some devices, we also observe
a smaller in-plane antidamping-like torque, with spin-torque conductivities up
to $4\times10^{3} ({\hbar}/2e) ({\Omega}m)^{-1}$, comparable to other TMD-based
systems. Both torques show no clear dependence on the WSe$_{2}$ thickness, as
expected for a Rashba system. Unexpectedly, we observe a strong in-plane
magnetic anisotropy - up to about $6.6\times10^{4} erg/cm^{3}$ - induced in
permalloy by the underlying hexagonal WSe$_{2}$ crystal. Using scanning
transmission electron microscopy, we confirm that the easy axis of the magnetic
anisotropy is aligned to the armchair direction of the WSe$_{2}$. Our results
indicate a strong interplay between the ferromagnet and TMD, and unveil the
nature of the spin-orbit torques in TMD-based devices. These findings open new
avenues for possible methods for optimizing the torques and the interaction
with interfaced magnets, important for future non-volatile magnetic devices for
data processing and storage.",2107.10621v2
2001-09-17,Ferromagnetic resonance in periodic particle arrays,"We report measurements of the ferromagnetic resonance (FMR) spectra of arrays
of submicron size periodic particle arrays of permalloy produced by
electron-beam lithography. In contrast to plane ferromagnetic films, the
spectra of the arrays show a number of additional resonance peaks, whose
position depends strongly on the orientation of the external magnetic field and
the interparticle interaction. Time-dependent micromagnetic simulation of the
ac response show that these peaks are associated with coupled exchange and
dipolar spin wave modes",0109307v1
2001-10-11,Enhanced Gilbert Damping in Thin Ferromagnetic Films,"Using a scattering matrix approach, the precession of the magnetization of a
ferromagnet is shown to transfer spins into adjacent normal metal layers. This
``pumping'' of spins slows down the precession corresponding to an enhanced
Gilbert damping factor in the Landau-Lifshitz equation. The damping is
expressed in terms of the scattering matrix of the ferromagnet-normal metal
interface, which is accessible to model and first-principles calculations. Our
estimates for permalloy thin films explain the trends observed in recent
experiments.",0110247v2
2002-01-04,Magnon modes for thin circular vortex state magnetic dot,"The magnetization in a magnetic microdot made from soft magnetic materials
can have a vortex-like ground state structure resulting from competition
between the exchange and dipolar interactions. Normal mode magnon frequencies
for such dots are calculated taking into account both exchange and
magnetostatic effects. The presence of a low-lying mode as well as doublet
structure with small splitting is demonstrated. Estimates of the mode
frequencies for permalloy dots are obtained, and the possibility of
experimental detection of such modes is discussed.",0201050v1
2003-04-14,Switching a spin-valve back and forth by current-induced domain wall motion,"We have studied the current-induced displacement of a domain wall (DW) in the
permalloy (Py) layer of a Co/Cu/Py spin valve structure at zero and very small
applied field. The displacement is in opposite direction for opposite dc
currents, and the current density required to move DW is only of the order of
10^6 A/cm^2. For H = 3 Oe, a back and forth DW motion between two stable
positions is observed. We also discuss the effect of an applied field on the DW
motion.",0304312v1
2004-04-13,Spin filtering in a hybrid ferromagnetic-semiconductor microstructure,"We fabricated a hybrid structure in which cobalt and permalloy micromagnets
produce a local in-plane spin-dependent potential barrier for high-mobility
electrons at the GaAs/AlGaAs interface. Spin effects are observed in ballistic
transport in the tens' millitesla range of the external field, and are
attributed to switching between Zeeman and Stern-Gerlach modes -- the former
dominating at low electron densities.",0404282v1
2004-08-27,Tunable magnetization damping in transition metal ternary alloys,"We show that magnetization damping in Permalloy, Ni80Fe20 (``Py''), can be
enhanced sufficiently to reduce post-switching magnetization precession to an
acceptable level by alloying with the transition metal osmium (Os). The damping
increases monotonically upon raising the Os-concentration in Py, at least up to
9% of Os. Other effects of alloying with Os are suppression of magnetization
and enhancement of in-plane anisotropy. Magnetization damping also increases
significantly upon alloying with the five other transition metals included in
this study (4d-elements: Nb, Ru, Rh; 5d-elements: Ta, Pt) but never as strongly
as with Os.",0408608v1
2005-06-24,New Memory Concept for Superconducting Electronics,"A new concept for nonvolatile superconducting memories is proposed. The
devices combine ferromagnetic dots for the storage of the data and Josephson
junctions for their readout. Good scalability is expected for large scale
integration. First memory cells have been implemented using 3
$\mu$m-Nb-technology and permalloy dots. Nonvolatile data storage at 300 K was
demonstrated.",0506647v2
2005-10-21,Magnetic Vortex Core Dynamics in a Ferromagnetic Dot,"We report direct imaging by means of x-ray photoemission electron microscopy
of the dynamics of magnetic vortices confined in micron-size circular Permalloy
dots that are 30 nm thick. The vortex core positions oscillate on a 10-ns
timescale in a self-induced magnetostatic potential well after the in-plane
magnetic field is turned off. The measured oscillation frequencies as a
function of the aspect ratio (thickness/radius) of the dots are in agreement
with theoretical calculations presented for the same geometry.",0510595v1
2005-11-02,Current-induced vortex displacement and annihilation in a single Permalloy disk,"The induced motion of a magnetic vortex in a micron-sized ferromagnetic disk
due to the DC current injection is studied by measuring planar Hall effect. The
DC current injection is found to induce the spin torque that sweeps the vortex
out of the disk at the critical current while bias magnetic field are applied.
The current-induced vortex core displacement deduced from the change in planar
Hall resistance is quantitatively consistent with theoretical prediction. Peak
structures similar to those originated from spin wave excitations are observed
in the differential planar Hall resistance curve.",0511040v1
2006-06-07,Ferromagnetic relaxation by magnon-induced currents,"A theory for calculating spin wave relaxation times based on the
magnon-electron interaction is developed. The theory incorporates a thin film
geometry and is valid for a large range of magnon frequencies and wave vectors.
For high conductivity metals such as permalloy, the wave vector dependent
damping constant approaches values as high as 0.2, showing the large magnitude
of the effect, and can dominate experimentally observed relaxation.",0606197v1
2006-06-21,Current-excited magnetization dynamics in narrow ferromagnetic wires,"We investigate the current-excited magnetization dynamics in a narrow
ferromagnetic Permalloy wire by means of Lorentz microscopy, together with the
results of simultaneous transport measurements. A detailed structural evolution
of the magnetization is presented as a function of the applied current density.
Local structural deformation, bidirectional displacement, and magnetization
reversal are found below the Curie temperature with increasing the current
density. We discuss probable mechanisms of observed features of the
current-excited magnetization dynamics.",0606547v1
2006-07-03,On-chip detection of ferromagnetic resonance of a single submicron permalloy strip,"We measured ferromagnetic resonance of a single submicron ferromagnetic
strip, embedded in an on-chip microwave transmission line device. The method
used is based on detection of the oscillating magnetic flux due to the
magnetization dynamics, with an inductive pick-up loop. The dependence of the
resonance frequency on applied static magnetic field agrees very well with the
Kittel formula, demonstrating that the uniform magnetization precession mode is
being driven.",0607036v1
2006-08-10,Spin Dynamics of a Magnetic Antivortex,"We report on a study of the dynamics of a magnetic antivortex in a submicron,
asteroid shaped, permalloy ferromagnet using micromagnetic simulations. As with
vortex states in disk and square geometries, a gyrotropic mode was found in
which a shifted antivortex core orbits about the center of the asteroid. Pulsed
magnetic fields were used to generate azimuthal or radial spin wave modes,
depending on the field orientation. The degeneracy of low frequency azimuthal
mode frequencies is lifted by gyrotropic motion of the antivortex core, and
restored by inserting a hole in the center of the particle to suppress this
motion. We briefly compare the dynamics of the vortex state of the asteroid to
the antivortex. The size dependence of the antivortex modes is reported.",0608245v1
2006-09-08,Large cone angle magnetization precession of an individual nanomagnet with dc electrical detection,"We demonstrate on-chip resonant driving of large cone-angle magnetization
precession of an individual nanoscale permalloy element. Strong driving is
realized by locating the element in close proximity to the shorted end of a
coplanar strip waveguide, which generates a microwave magnetic field. We used a
microwave frequency modulation method to accurately measure resonant changes of
the dc anisotropic magnetoresistance. Precession cone angles up to $9^{0}$ are
determined with better than one degree of resolution. The resonance peak shape
is well-described by the Landau-Lifshitz-Gilbert equation.",0609190v1
2006-10-09,Single-domain versus two-domain configuration in thin ferromagnetic prisms,"Thin ferromagnetic elements in the form of rectangular prisms are
theoretically investigated in order to study the transition from single-domain
to two-domain state, with changing the in-plane aspect ratio p. We address two
main questions: first, how general is the transition; second, how the critical
value p_c depends on the physical parameters. We use two complementary methods:
discrete-lattice calculations and a micromagnetic continuum approach. Ultrathin
films do not appear to split in two domains. Instead, thicker films may undergo
the above transition. We have used the continuum approach to analyze recent
Magnetic Force Microscopy observations in 30 nm-thick patterned Permalloy
elements, finding a good agreement for p_c.",0610233v1
2006-11-25,Dynamics of Vortex Core Switching in Ferromagnetic Nanodisks,"Dynamics of magnetic vortex core switching in nanometer-scale permalloy disk,
having a single vortex ground state, was investigated by micromagnetic
modeling. When an in-plane magnetic field pulse with an appropriate strength
and duration is applied to the vortex structure, additional two vortices, i.e.,
a circular- and an anti-vortex, are created near the original vortex core.
Sequentially, the vortex-antivortex pair annihilates. A spin wave is created at
the annihilation point and propagated through the entire element; the relaxed
state for the system is the single vortex state with a switched vortex core.",0611640v1
2007-12-17,Proximity effect-assisted absorption of spin currents in superconductors,"The injection of pure spin current into superconductors by the dynamics of a
ferromagnetic contact is studied theoretically. Taking into account suppression
of the order parameter at the interfaces (inverse proximity effect) and the
energy-dependence of spin-flip scattering, we determine the
temperature-dependent ferromagnetic resonance linewidth broadening. Our results
agree with recent experiments in Nb|permalloy bilayers [C. Bell et al.,
arXiv:cond-mat/0702461].",0712.2814v1
2008-09-26,Domain wall displacement in Py square ring for single nanometric magnetic bead detection,"A new approach based on the domain wall displacement in confined
ferromagnetic nanostructures for attracting and sensing a single nanometric
magnetic particles is presented. We modeled and experimentally demonstrated the
viability of the approach using an anisotropic magnetoresistance device made by
a micron-size square ring of Permalloy designed for application in magnetic
storage. This detection concept can be suitable to biomolecular recognition,
and in particular to single molecule detection.",0809.4649v1
2008-12-02,Independent magnetization behavior of a ferromagnetic metal/semiconductor hybrid system,"We report the discovery of an effect where two ferromagnetic materials, one
semiconductor ((Ga,Mn)As) and one metal (permalloy), can be directly deposited
on each other and still switch their magnetization independently. We use this
independent magnetization behavior to create various resistance states
dependent on the magnetization direction of the individual layers. At zero
magnetic field a two layer device can reach up to four non-volatile resistance
states.",0812.0455v1
2009-01-13,Refractive index and Snell's Law for Dipolar-Exchange Spin-Waves in a Confined Planar Structure,"We derived the analytical forms of refractive index and Snell law for
dipolar-exchange spin waves of reflection and refraction at a magnetically
heterogeneous interface in a geometrically confined planer structure composed
of different magnetic thin films from a microscopic scattering approach. A
novel behavior, the optical total reflection, was demonstrated for spin waves
with a specific interface between Yttrium iron garnet (Y3Fe5O12) and Permalloy
(Ni80Fe20), by analytical and micromagnetic numerical calculations.",0901.1700v2
2009-01-15,Vortex stabilization in magnetic trilayer dots,"The magnetization reversal and spin structure in circular
Co/insulator/Ni80Fe20 trilayer dots has been investigated numerically. The
effect of dipolar coupling between a soft ferromagnetic Permalloy (Py=Ni80Fe20)
layer and a hard ferromagnetic Cobalt layer inside one stack is studied. We
find either a stabilization or even a triggering of the vortex state in the Py
layer due to the magnetic stray field of the Co layer, while the Co
magnetization remains in a single-domain state. Furthermore, for thin Py layers
a 360 deg-domain wall is observed. We construct a phase diagram, where regions
of vortex stabilization, triggering, and occurrence of a 360 deg domain wall
are marked.",0901.2209v1
2009-04-06,Characterisation of Ferromagnetic Contacts to Carbon Nanotubes,"We present an investigation of different thin-film evaporated ferromagnetic
materials for their suitability as electrodes in individual single-wall and
multi-wall carbon nanotube-based spin devices. Various electrode shapes made
from permalloy (Ni_{81}Fe_{19}), the diluted ferromagnet PdFe, and PdFe/Fe
bilayers are studied for both their micromagnetic properties and their contact
formation to carbon nanotubes. Suitable devices are tested in low-temperature
electron transport measurements, displaying the typical tunneling
magnetoresistance of carbon nanotube pseudo spin valves.",0904.0907v2
2009-08-14,Spin-wave interference in three-dimensional rolled-up ferromagnetic microtubes,"We have investigated spin-wave excitations in rolled-up Permalloy microtubes
using microwave absorption spectroscopy. We find a series of quantized
azimuthal modes which arise from the constructive interference of Damon-Eshbach
type spin waves propagating around the circumference of the microtubes, forming
a spin-wave resonator. The mode spectrum can be tailored by the tube's radius
and number of rolled-up layers.",0908.2082v1
2009-10-14,Surface spin flip probability of mesoscopic Ag wires,"Spin relaxation in mesoscopic Ag wires in the diffusive transport regime is
studied via nonlocal spin valve and Hanle effect measurements performed on
permalloy/Ag lateral spin valves. The ratio between momentum and spin
relaxation times is not constant at low temperatures. This can be explained
with the Elliott-Yafet spin relaxation mechanism by considering the momentum
surface relaxation time as being temperature dependent. We present a model to
separately determine spin flip probabilities for phonon, impurity and surface
scattering and find that the spin flip probability is highest for surface
scattering.",0910.2744v3
2009-11-13,Nano-Torsional Resonator Torque Magnetometry,"Magnetic torque is used to actuate nano-torsional resonators, which are
fabricated by focused-ion-beam milling of permalloy coated silicon nitride
membranes. Optical interferometry is used to measure the mechanical response of
two torsion modes at resonance, which is proportional to the magnetization
vector of the nanomagnetic volume. By varying the bias magnetic field, the
magnetic behavior can be measured with excellent sensitivity ($\approx 10^8
\mu_B$) for single magnetic elements.",0911.2517v2
2010-04-15,Ground-state configurations in ferromagnetic nanotori,"Magnetization ground states are studied in toroidal nanomagnets. The
energetics associated to the ferromagnetic, vortex and onion-like
configurations are explicitly computed. The analysis reveals that the vortex
appears to be the most prominent of such states, minimizing total energy in
every torus with internal radius $r\gtrsim10\,{\rm nm}$ (for Permalloy). For
$r\lesssim10\,{\rm nm}$ the vortex remains the most favorable pattern whenever
$R/\ell_{ex}\gtrsim1.5$ ($R$ is the torus external radius and $\ell_{ex}$ is
the exchange length), being substituted by the ferromagnetic state whenever
$R/\ell_{ex}\lesssim1.5$.",1004.2689v1
2010-12-18,Conduction Electron Spin-Flipping at Sputtered Co(90)Fe(10)/Cu Interfaces,"From measurements of the current-perpendicular-to-plane (CPP)
magnetoresistance of ferromagnetically coupled [Co(90)Fe(10)/Cu]xn multilayers,
within sputtered Permalloy-based double exchange biased spin-valves, we
determine the parameter delta[(Co(90)Fe(10))/Cu] = 0.19 +/- 0.04 that sets the
probability P of spin-flipping at a Co(90)Fe(10)/Cu interface via the equation
P = 1 - exp(-delta).",1012.4099v1
2011-08-05,Thermoelectric detection of ferromagnetic resonance of a nanoscale ferromagnet,"We present thermoelectric measurements of the heat dissipated due to
ferromagnetic resonance of a Permalloy strip. A microwave magnetic field,
produced by an on-chip coplanar strip waveguide, is used to drive the
magnetization precession. The generated heat is detected via Seebeck
measurements on a thermocouple connected to the ferromagnet. The observed
resonance peak shape is in agreement with the Landau-Lifshitz-Gilbert equation
and is compared with thermoelectric finite element modeling. Unlike other
methods, this technique is not restricted to electrically conductive media and
is therefore also applicable to for instance ferromagnetic insulators.",1108.1286v1
2011-08-30,Spin Wave Diffraction and Perfect Imaging of a Grating,"We study the diffraction of Damon-Eshbach-type spin waves incident on a
one-dimensional grating realized by micro slits in a thin permalloy film. By
means of time-resolved scanning Kerr microscopy we observe unique diffraction
patterns behind the grating which exhibit replications of the spin-wave field
at the slits. We show that these spin-wave images, with details finer than the
wavelength of the incident Damon-Eshbach spin wavelength, arise from the
strongly anisotropic spin wave dispersion.",1108.5883v1
2012-02-29,Spin wave modes in magnetic nanodisks under in-plane magnetic field,"The size dependence of spin wave modes in a circular Permalloy (Py) nanodisk
under an in-plane magnetic field is systematically studied by using
micromagnetics simulations. We show that as the disk diameter is increased, the
resonance frequency of the backward mode deceases while that of the uniform
mode increases. The avoided crossing of resonance frequencies of the uniform
mode and the backward mode appears in the plot of the size dependence of
resonance frequencies and the backward mode turns into the so-called ""edge
mode"" for large nanodisks.",1202.6464v1
2012-03-28,Charge Imbalance and Crossed Andreev reflection in Py/Ta Devices,"Crossed Andreev reflection in a lateral spin valve geometry device is an
aspect of considerable recent interest, particularly with regards to Cooper
pair splitting experiments to realize solid state quantum entanglement. In this
work, devices are fabricated consisting of two ferromagnetic permalloy (Py)
electrodes contacted by a overlaid perpendicular superconducting Ta electrode,
of variable lateral in-plane offset within the expected BCS superconducting
coherence length $\xi_0$. Experimental electrical transport measurements are
presented of local and nonlocal conduction, showing characteristics of
non-local or crossed Andreev reflection in the superconducting state at low
temperatures in addition to nonlocal effects divergent for T$\rightarrow$T$_c$
attributed to nonlocal charge imbalance.",1203.6296v1
2012-04-05,The influence of individual lattice defects on the domain structure in magnetic antidot lattices,"We numerically and experimentally investigate the influence of single defects
consisting of a missing antidot on the spin configurations in rectangular
permalloy antidot lattices. The introduction of such lattice defects leads to
the nucleation of complex domain structures after the decay of a saturating
magnetic field. Micromagnetic simulations yield four typical domain
configurations around the defect having distinct energy densities. The
existence of the four spin configurations is confirmed by magnetic force
microscopy on antidot lattices containing individual defects.",1204.1183v2
2012-05-25,Spin wave amplification driven by heat flow: the role of damping and exchange interaction,"In this article we report on micromagnetic simulations performed on a
permalloy nanostructure in presence of a uniform thermal gradient. Our
numerical simulations show that heat flow is an effective mean to compensate
the damping, and that the gradients at which spin-wave amplification is
observed are experimentally accessible. In particular, we have studied the role
of the Gilbert damping parameter on spin-wave amplification.",1205.5650v2
2012-07-19,Anatomy of Demagnetizing and Exchange Fields in Magnetic Nanodots Influenced by 3D Shape Modifications,"Hysteresis loops of 3D ferromagnetic permalloy nano-half-balls (dots) with
100 nm base diameter have been examined by means of LLG micromagnetic
simulations and finite element methods. Tests were carried out with two
orthogonal directions of the externally applied field at 10 kA/(m.ns) field
sweeping speed. The comparison of samples with different 3D modifications at
the sub-10nm scale, accessible by nowadays lithographic techniques, enables
conclusions about different mechanisms of competition between demagnetizing and
exchange fields. Design paradigms provided here can find possible applications
in magneto-electronic devices.",1207.4673v1
2013-01-28,Pinning of a Bloch point by an atomic lattice,"Bloch points are magnetic topological defects. The discrete nature of a
magnetic lattice creates a periodic potential that can pin a Bloch point. The
pinning force is of the order of the exchange constant, a few piconewtons in a
typical ferromagnet (permalloy). A domain wall containing a Bloch point can
have a sizable depinning field in the tens of oersted.",1301.6452v2
2013-03-30,Features of amplification of dipole magnetic field with linear ferromagnetic concentrator,"Amplification of a low frequency magnetic field from a dipole source by means
of linear ferromagnetic concentrator of different dimensions (permalloy micro
wire) has been investigated experimentally. The results obtained strengthen the
validity of the analytical relation for amplification which allows for
nonlinear dependence of the magnetic permeability upon the value and
distribution of the dipole field over concentrator length.",1304.0111v1
2013-06-05,Equilibrium states of soft magnetic hemispherical shell,"The ground state of hemispherical permalloy magnetic shell is studied. There
exist two magnetic phases: the onion state and the vortex one. The phase
diagram is systematically analyzed in a wide range of geometrical parameters.
Possible transitions between different phases are analyzed using the
combination of analytical calculations and micromagnetic simulations.",1306.1249v2
2013-09-29,Magnetic shield of PMT used in DAMPE electromagnetic calorimeter,"The magnetic characteristics of photomultiplier tube R5610A-01 are studied in
this paper. The experimental data shows that the gain of R5610A-01 loses about
53% when the magnetic field is 3G along its +X axis. A cylinder of one-layer
permalloy strip is able to reduce the effect of 3G magnetic field on the PMT's
gain to less than 1%.",1309.7638v4
2013-10-23,Magnetization Characteristic of Ferromagnetic Thin Strip by Measuring Anisotropic Magnetoresistance and Ferromagnetic Resonance,"The magnetization characteristic in a permalloy thin strip is investigated by
electrically measuring the anisotropic magnetoresistance and ferromagnetic
resonance in in-plane and out-of-plane configurations. Our results indicate
that the magnetization vector can rotate in the film plane as well as out of
the film plane by changing the intensity of external magnetic field of certain
direction. The magnetization characteristic can be explained by considering
demagnetization and magnetic anisotropy. Our method can be used to obtain the
demagnetization factor, saturated magnetic moment and the magnetic anisotropy.",1310.6117v1
2014-02-11,Fundamental energy limits in the physics of small-scale binary switches,"Binary switches are the basic element of modern digital computers. In this
paper we discuss the role of switching procedure with reference to the
fundamental limits in minimum energy dissipation. We show that the minimum
energy depends on the switching procedure and test this result with
micromagnetic simulations of a nanoscale switch realized with single
cylindrical element of permalloy (NiFe). Finally we establish a relation
between minimum energy and switching error probability.",1403.1800v1
2014-07-21,Josephson junction with a magnetic vortex,"We have studied Josephson tunneling through a circularly polarized micron or
submicron-size disk of a soft ferromagnetic material. Such a disk contains a
vortex that exhibits rich classical dynamics and has recently been proposed as
a tool to study quantum dynamics of the nanoscale vortex core. The change in
the Josephson current that is related to a tiny displacement of the vortex core
has been computed analytically and plotted numerically for permalloy disks used
in experiments. It is shown that a Josephson junction with a magnetic disk in
the vortex state can be an interesting physical system that may be used to
measure the nanoscale motion of the magnetic vortex.",1407.5419v1
2014-07-29,Faceting Oscillations in Nano-Ferroelectrics,"We observe periodic faceting of 8-nm diameter ferroelectric disks on a 10 s
time-scale when thin Pb(Zr0.52Ti0.48)O3 (PZT) film is exposed to constant
high-resolution transmission electron microscopy (HRTEM) beams. The oscillation
is between circular disk geometry and sharply faceted hexagons. The behavior is
analogous to that of spin structure and magnetic domain wall velocity
oscillations in permalloy [A. Bisig et al., Nature Commun. 4, 2328 (2013)],
involving overshoot and de-pinning from defects [C. P. Amann, et al., J. Rheol.
57, 149-175 (2013)].",1407.7646v1
2015-04-22,Fork stamping of pristine carbon nanotubes onto ferromagnetic contacts for spin-valve devices,"We present a fabrication scheme called 'fork stamping' optimized for the dry
transfer of individual pristine carbon nanotubes (CNTs) onto ferromagnetic
contact electrodes fabricated by standard lithography. We demonstrate the
detailed recipes for a residue-free device fabrication and in-situ current
annealing on suspended CNT spin-valve devices with ferromagnetic Permalloy (Py)
contacts and report preliminary transport characterization and
magnetoresistance experiments at cryogenic temperatures. This scheme can
directly be used to implement more complex device structures, including
multiple gates or superconducting contacts.",1504.05693v1
2015-10-25,Dependence of transverse magneto-thermoelectric effects on inhomogeneous magnetic fields,"Transverse magneto-thermoelectric effects are studied in permalloy thin films
grown on MgO substrates. We find that small parasitic magnetic fields below 1
Oe can produce artifacts of the order of 1 % of the amplitude of the
anisotropic magneto-thermopower which is also detected in the experiments. The
measured artifacts reveal a new source of uncertainties for the detection of
the transverse spin Seebeck effect. Taking these results into account we
conclude that the contribution of the transverse spin Seebeck effect to the
detected voltages is below the noise level of 20 nV.",1510.07241v1
2016-01-17,Experimental observation of spin to charge current conversion at non-magnetic metal/Bi2O3 interfaces,"We here demonstrate the interfacial spin to charge current conversion by
means of spin pumping from a ferromagnetic Permalloy (Py: Ni80Fe20) to a
Cu/Bi2O3 interface. A clear signature of the spin to charge current conversion
was observed in voltage spectrum of a Py/Cu/Bi2O3 trilayer film whereas no
signature in a Py/Cu and Py/Bi2O3 bilayer films. We also found that the
conversion coefficient strongly depended on Cu thickness, reflecting the
thickness dependent momentum relaxation time in Cu layer.",1601.04292v1
2016-02-22,Exchange magnon induced resistance asymmetry in permalloy spin-Hall oscillators,"We investigate magnetization dynamics in a spin-Hall oscillator using a
direct current measurement as well as conventional microwave spectrum analysis.
When the current applies an anti-damping spin-transfer torque, we observe a
change in resistance which we ascribe to the excitation of incoherent exchange
magnons. A simple model is developed based on the reduction of the effective
saturation magnetization, quantitatively explaining the data. The observed
phenomena highlight the importance of exchange magnons on the operation of
spin-Hall oscillators.",1602.06710v1
2016-10-19,Resonant Magnetization Switching Conditions of an Exchange-coupled Bilayer under Spin Wave Excitation,"We systematically investigated the spin wave-assisted magnetization switching
(SWAS) of a L10-FePt / Ni81Fe19 (Permalloy; Py) exchange-coupled bilayer using
a pulse-like rf field (hrf) and mapped the switching events in the magnetic
field (H) - hrf frequency (f) plane to reveal the switching conditions. The
switching occurred only in a limited region following the dispersion
relationship of the perpendicular standing spin wave (PSSW) modes in Py. The
results indicate that SWAS is a resonant magnetization switching process, which
is different from the conventional microwave assisted switching, and has the
potential to be applied to selective switching for multilevel recording media.",1610.05864v1
2018-06-18,Relation between unidirectional spin Hall magnetoresistance and spin current-driven magnon generation,"We perform electronic measurements of unidirectional spin Hall
magnetoresistance (USMR) in a Permalloy/Pt bilayer, in conjunction with
magneto-optical Brillouin light spectroscopy of spin current-driven magnon
population. We show that the current dependence of USMR closely follows the
dipolar magnon density, and that both dependencies exhibit the same scaling
over a large temperature range of 80-400 K. These findings demonstrate a close
relationship between spin current-driven magnon generation and USMR, and
indicate that the latter is likely dominated by the dipolar magnons.",1806.06581v1
2014-06-23,Fast minute magnetic field coil for time-resolved nanospintronics,"Nanospintronic and related research often requires the application of fast
rising magnetic field pulses in the plane of the studied planar structure. We
have designed and fabricated sub-milimeter-sized coils capable of delivering
pulses of the magnetic field up to ~ 500 Oe in the plane of the sample with the
rise time of order of 10 ns. The placement of the sample above the coil allows
for an easy access to its surface with manipulators or light beams for, e.g.,
Kerr microscopy. We use the fabricated coil to drive magnetic domain walls in 1
${\mu}$ m wide permalloy wires and measure magnetic domain wall velocity as a
function of the applied magnetic field.",1406.5901v1
2018-12-26,Probing the Relationship between Anisotropic Magnetoresistance and Magnetization of ferromagnetic films,"The anisotropic magnetoresistance (AMR) in thin permalloy strips was
calculated at each steps during magnetization by the finite element method. The
magnetization at equilibrium under different external fields was obtained by
micromagnetic simulations, while the resistance with different magnetization
was obtained by solving the Poisson equations iteratively until
self-consistence. We find that the relation between magnetization and AMR
deviates from the Stoner-Wohlfarth prediction when the magnetization is reduced
from saturation. The reason is that the demagnetization is not necessarily from
coherent rotation of the magnetic moment. We conclude that it is necessary to
use numeric simulations to optimize the responses of AMR sensors.",1812.10294v1
2016-03-23,"Nucleation, imaging and motion of magnetic domain walls in cylindrical nanowires","We report several procedures for the robust nucleation of magnetic domain
walls in cylindrical permalloy nanowires. Specific features of the magnetic
force microscopy contrast of such soft wires are discussed, with a view to
avoid the misinterpretation of the magnetization states. The domain walls could
be moved under quasistatic magnetic fields in the range 0.1--10 mT.",1603.07240v1
2016-12-16,Relaxation mechanism driven by spin angular momentum absorption throughout antiferromagnetic phase transition in NiFe surface oxides,"We report an alternative mechanism for the physical origin of the
temperature-dependent ferromagnetic relaxation of Permalloy (NiFe) thin films.
Through spin-pumping experiments, we demonstrate that the peak in the
temperature-dependence of NiFe damping can be understood in terms of enhanced
spin angular momentum absorption at the magnetic phase transition in
antiferromagnetic surface-oxidized layers. These results suggest new avenues
for the investigation of an incompletely-understood phenomenon in physics.",1612.05556v1
2003-12-02,Studies of dc Current-Driven Switching in Py/N/Py magnetic nanopillars,"We provide new data on current-driven switching in Permalloy (Py = Ni84Fe16)
based nanopillars at room temperature and 4.2K that confirm and extend
previously published work. We present data for both uncoupled and
antiferromagnetically coupled samples. The latter confirm prior results for
Co/Cu/Co. We show that inserting sufficiently strong spin-flip-scattering into
the Cu layer eliminates hysteretic current-driven switching. This result may
have ramifications for understanding current-driven switching.",0312078v1
2017-01-06,Imaging magnetic vortex configurations in ferromagnetic nanotubes,"We image the remnant magnetization configurations of CoFeB and permalloy
nanotubes (NTs) using x-ray magnetic circular dichroism photo-emission electron
microscopy. The images provide direct evidence for flux-closure configurations,
including a global vortex state, in which magnetization points
circumferentially around the NT axis. Furthermore, micromagnetic simulations
predict and measurements confirm that vortex states can be programmed as the
equilibrium remnant magnetization configurations by reducing the NT aspect
ratio.",1701.01685v1
2019-08-21,Artificial Spin Ice Phase-Change Memory Resistors,"We study the implications of the anisotropic magnetic resistance on permalloy
nanowires, and in particular on the property of the resistance depending on the
type of lattice. We discuss how the internal spin configuration of artificial
spin ice nanowires can affect their effective resistive state, and which
mechanisms can introduce a current-dependent effect dynamic resistive state. We
discuss a spin-induced thermal phase-change mechanism, and an athermal
domain-wall spin inversion. In both cases we observe memory behavior
reminiscent of a memristor, with an I-V hysteretic pinched behavior.",1908.08073v1
2020-05-11,Chiral Walker breakdown in the U-shaped Permalloy nanotube,"The motion of transverse domain walls (DWs) in U-shaped ferromagnetic
nanotube which owns two different geometric confinements were investigated by
micromagnetic simulation. Driven by unidirectional magnetic fields, the
chirality-dependent DW structure and velocity under low fields and two phases
of chiral Walker breakdown processes under high fields were observable,
respectively. All these chirality-dependent behaviors can be attributed to the
different dynamics of magnetizations in geometric confinements. Additionally,
DW structures have different responses and sensitivity to applied fields,
leading to a hierarchy and complex Walker breakdown processes. This supplies a
new perspective for manipulating DW chirality.",2005.05162v2
2021-09-17,Fabricacion de un magnetron sputtering para deposito de peliculas nanometricas magneticas,"This paper presents the development of scientific instrumentation for the
fabrication of ferromagnetic thin films, by sputtering technique, for the use
of 2-inch-diameter targets. Thin films were deposited using Permalloy alloy
(Ni80Fe20) as ferromagnetic material at room temperature on Si (001)
substrates. The film thicknesses were measured with profilometry and a
deposition rate for this alloy of 16.2 nm/min was calculated. Scanning electron
microscopy showed a continuous film formation and a chemical composition
similar to the target",2109.08649v1
2022-11-04,Observation of Spin Current Hermiticity,"The spin Hall effect is one of the most relevant effects in spintronics and
the key to conversion from charge current into spin current. We report here a
phenomenon, which appears in response to the spin Hall effect and represents
the anti-polarization of the spin current due to the coupling between
interfacial magnetic anisotropies. Such an effect produces a Hermitian spin
current. We realized experiments on permalloy (Py) and Cobalt (Co) bilayers to
discuss this phenomenon.",2211.02334v1
2023-06-05,Observation of anisotropic magneto-inductance effect,"We have discovered a new phenomenon that inductance oscillates as a function
of the angle between an in-plane magnetic field and an electric current
direction in permalloy films, which we have named ""the anisotropic
magneto-inductance (AML) effect"". We have investigated the dependences of the
AML effect on the size and voltage. The length, frequency, and amplitude
dependences suggest that the AML effect should be evaluated in terms of
""inductivity"". Inductors based on this AML effect have the potential to be
variable, on-chip, and one billion times smaller than the small commercial
inductor.",2306.02757v1
2024-03-11,Magnetic vortex polarity reversal induced gyrotropic motion spectrum splitting in a ferromagnetic disk,"We investigate the gyrotropic motion of the magnetic vortex core in a chain
of a few micron-sized Permalloy disks by electrical resistance measurement with
amplitude-modulated magnetic field. We observe a distinctive splitting of the
resistance peak due to the resonant vortex-core motion under heightened radio
frequency (RF) magnetic field excitation. Our micromagnetic simulation
identifies the splitting of the resonant peak as an outcome of vortex polarity
reversal under substantial RF amplitudes. This study enhances our understanding
of nonlinear magnetic vortex dynamics amidst large RF amplitudes and proposes a
potential pathway for spintronic neural computing thanks to their unique and
controllable magnetization dynamics.",2403.06491v1
2024-03-21,Efecto Hall de espin inverso en peliculas de Nb Mo y Bi por bombeo de espin,"The inverse spin Hall effect used for detection of spin currents was observed
by voltage measurements in bilayers of normal metal (NM)/ferromagnetic metal
(FM), using Nb, Mo and Bi as normal metal and Permalloy (Py,
Ni$_{81}$Fe$_{19}$) as ferromagnetic metal. The spin current was generated by
the spin pumping effect with ferromagnetic resonance. The samples were
deposited by dc magnetron sputtering at room temperature on Si (001)
substrates. The three bilayers of Nb/Py, Mo/Py and Bi/Py had a spin-orbit
coupling large enough to observe the voltage generation by spin Hall effect",2403.17976v1
2004-07-14,An ab-initio theoretical investigation of the soft-magnetic properties of permalloys,"We study Ni80Fe20-based permalloys with the relativistic spin-polarized
Korringa-Kohn-Rostoker electronic structure method. Treating the compositional
disorder with the coherent potential approximation, we investigate how the
magnetocrystalline anisotropy, K, and magnetostriction, lambda, of Ni-rich
Ni-Fe alloys vary with the addition of small amounts of non-magnetic transition
metals, Cu and Mo. From our calculations we follow the trends in K and lambda
and find the compositions of Ni-Fe-Cu and Ni-Fe-Mo where both are near zero.
These high permeability compositions of Ni-Fe-Cu and Ni-Fe-Mo match well with
those discovered experimentally. We monitor the connection of the magnetic
anisotropy with the number of minority spin electrons, Nmin. By raising Nmin
via artificially increasing the band-filling of Ni80Fe20, we are able to
reproduce the key features that underpin the magnetic softening we find in the
ternary alloys. The effect of band-filling on the dependence of
magnetocrystalline anisotropy on atomic short-range order in Ni80Fe20 is also
studied. Our calculations, based on a static concentration wave theory,
indicate that the susceptibility of the high permeability of the Ni-Fe-Cu and
Ni-Fe-Mo alloys to their annealing conditions is also strongly dependent on the
alloys' compositions. An ideal soft magnet appears from these calculations.",0407355v1
2009-05-12,Magnetotransport effects of ultrathin Ni80Fe20 films probed in-situ,"We have investigated the magnetoresistance of Permalloy (Ni80Fe20) films with
thicknesses ranging from a single monolayer to 12 nm, grown on Al2O3, MgO and
SiO2 substrates. Growth and transport measurements were carried out under
cryogenic conditions in UHV. Applying in-plane magnetic vector fields up to 100
mT, the magnetotransport properties are ascertained during growth. With
increasing thickness the films exhibit a gradual transition from tunneling
magnetoresistance to anisotropic magnetoresistance. This corresponds to the
evolution of the film structure from separated small islands to a network of
interconnected grains as well as the transition from superparamagnetic to
ferromagnetic behavior of the film. Using an analysis based on a theoretical
model of the island growth, we find that the observed evolution of the
magnetoresistance in the tunneling regime originates from the changes in the
island size distribution during growth. Depending on the substrate material,
significant differences in the magnetoresistance response in the transition
regime between tunneling magnetoresistance and anisotropic magnetoresistance
were found. We attribute this to an increasingly pronounced island growth and
slower percolation process of Permalloy when comparing growth on SiO2, MgO and
Al2O3 substrates. The different growth characteristics result in a markedly
earlier onset of both tunneling magnetoresistance and anisotropic
magnetoresistance for SiO2. For Al2O3 in particular the growth mode results in
a structure of the film containing two different contributions to the
ferromagnetism which lead to two distinct coercive fields in the high thickness
regime.",0905.1819v2
2011-07-28,Identification and selection rules of the spin-wave eigen-modes in a normally magnetized nano-pillar,"We report on a spectroscopic study of the spin-wave eigen-modes inside an
individual normally magnetized two layers circular nano-pillar
(Permalloy$|$Copper$|$Permalloy) by means of a Magnetic Resonance Force
Microscope (MRFM). We demonstrate that the observed spin-wave spectrum
critically depends on the method of excitation. While the spatially uniform
radio-frequency (RF) magnetic field excites only the axially symmetric modes
having azimuthal index $\ell=0$, the RF current flowing through the
nano-pillar, creating a circular RF Oersted field, excites only the modes
having azimuthal index $\ell=+1$. Breaking the axial symmetry of the
nano-pillar, either by tilting the bias magnetic field or by making the pillar
shape elliptical, mixes different $\ell$-index symmetries, which can be excited
simultaneously by the RF current. Experimental spectra are compared to
theoretical prediction using both analytical and numerical calculations. An
analysis of the influence of the static and dynamic dipolar coupling between
the nano-pillar magnetic layers on the mode spectrum is performed.",1107.5699v2
2013-01-16,Self-induced inverse spin Hall effect in permalloy at room temperature,"Inverse spin Hall effect (ISHE) allows the conversion of pure spin current
into charge current in nonmagnetic materials (NM) due to spin-orbit interaction
(SOI). In ferromagnetic materials (FM), SOI is known to contribute to anomalous
Hall effect (AHE), anisotropic magnetoresistance (AMR), and other
spin-dependent transport phenomena. However, SOI in FM has been ignored in ISHE
studies in spintronic devices, and the possibility of ""self-induced ISHE"" in FM
has never been explored until now. In this paper, we demonstrate the
experimental verification of ISHE in FM. We found that the spin-pumping-induced
spin current in permalloy (Py) film generates a transverse electromotive force
(EMF) in the film itself, which results from the coupling of spin current and
SOI in Py. The control experiments ruled out spin rectification effect and
anomalous Nernst effect as the origin of the EMF.",1301.3580v5
2014-10-21,Neutron Reflectometry Studies on Magnetic Stripe Domains in Permalloy/Superconductor bilayers,"We explored changes in magnetic domain structures in a magnetic layer due to
the onset of the superconductivity of an adjacent superconductive layer using
neutron reflectometry. Magnetic domain structures in 1~$\mu$m thick permalloy
(Py) films were studied as functions of magnetic field, temperature and under
the influence of the onset of superconductivity in a neighboring layer. Bragg
peaks in the off-specular scattering were observed at low fields following
saturation with an in-plane field, which are attributed to the quasi-parallel
magnetic stripes along the field direction. During the magnetization reversal
from saturation, the stripe pattern shows increases in the period, the
transverse coherence length (\textit{i.e.}, perpendicular to the stripes) and
the amplitude of the out-of-plane magnetization component. The coherence length
of the magnetic stripes is anisotropic in the remnant state with the
longitudinal coherence length (\textit{i.e.}, along the stripes) being larger
than the transverse one. The stripe period shows a weak temperature dependence
between 300~K and 3~K, but no abrupt change in the period is observed when the
temperature crosses the superconducting critical temperature.",1410.5520v1
2015-04-29,Role of transparency of platinum-ferromagnet interface in determining intrinsic magnitude of spin Hall effect,"The spin Hall effect (SHE) converts charge current to pure spin currents in
orthogonal directions in materials that have significant spin-orbit
coupling.The efficiency of the conversion is described by the spin Hall Angle
(SHA). The SHA can most readily be inferred by using the generated spin
currents to excite or rotate the magnetization of ferromagnetic films or
nano-elements via spin-transfer torques.Some of the largest spin torque derived
spin Hall angles (ST-SHA) have been reported in platinum. Here we show, using
spin torque ferromagnetic resonance (ST-FMR) measurements, that the
transparency of the Pt-ferromagnet interface to the spin current plays a
central role in determining the magnitude of the ST-SHA. We measure a much
larger ST-SHA in Pt/cobalt (~0.11) compared to Pt/permalloy (~0.05) bilayers
when the interfaces are assumed to be completely transparent. Taking into
account the transparency of these interfaces, as derived from spin-mixing
conductances, we find that the intrinsic SHA in platinum has a much higher
value of 0.19 +- 0.04 as compared to the ST-SHA. The importance of the
interface transparency is further exemplified by the insertion of atomically
thin magnetic layers at the Pt/permalloy interface that we show strongly
modulates the magnitude of the ST-SHA.",1504.07929v1
2015-12-01,Magnetization reversal of an individual exchange biased permalloy nanotube,"We investigate the magnetization reversal mechanism in an individual
permalloy (Py) nanotube (NT) using a hybrid magnetometer consisting of a
nanometer-scale SQUID (nanoSQUID) and a cantilever torque sensor. The Py NT is
affixed to the tip of a Si cantilever and positioned in order to optimally
couple its stray flux into a Nb nanoSQUID. We are thus able to measure both the
NT's volume magnetization by dynamic cantilever magnetometry and its stray flux
using the nanoSQUID. We observe a training effect and temperature dependence in
the magnetic hysteresis, suggesting an exchange bias. We find a low blocking
temperature $T_B = 18 \pm 2$ K, indicating the presence of a thin
antiferromagnetic native oxide, as confirmed by X-ray absorption spectroscopy
on similar samples. Furthermore, we measure changes in the shape of the
magnetic hysteresis as a function of temperature and increased training. These
observations show that the presence of a thin exchange-coupled native oxide
modifies the magnetization reversal process at low temperatures. Complementary
information obtained via cantilever and nanoSQUID magnetometry allows us to
conclude that, in the absence of exchange coupling, this reversal process is
nucleated at the NT's ends and propagates along its length as predicted by
theory.",1512.00199v1
2016-02-01,Facet-dependent giant spin orbit torque in single crystalline antiferromagnetic Ir-Mn / ferromagnetic permalloy bilayers,"There has been considerable interest in spin-orbit torques for the purpose of
manipulating the magnetization of ferromagnetic (FM) films or nano-elements for
spintronic technologies. Spin-orbit torques are derived from spin currents
created from charge currents in materials with significant spin-orbit coupling
that diffuse into an adjacent FM material. There have been intensive efforts to
search for candidate materials that exhibit large spin Hall angles, i.e.
efficient charge to spin current conversion. Here we report, using spin torque
ferromagnetic resonance, the observation of a giant spin Hall angle of up to
~0.35 in (100) oriented single crystalline antiferromagnetic (AF) IrMn3 thin
films, coupled to ferromagnetic permalloy layers, and a spin Hall angle that is
about three times smaller in (111) oriented films. For the (100) oriented
samples we show that the magnitude of the spin Hall angle can be significantly
changed by manipulating the populations of the various AF domains through field
annealing. Using ab-initio calculations we show that the triangular AF
structure of IrMn3 gives rise to a substantial intrinsic spin Hall conductivity
that is three times larger for the (100) than for the (111) orientations,
consistent with our experimental findings.",1602.00670v1
2016-02-19,A systematic study of magnetodynamic properties at finite temperatures in doped permalloy from first principles calculations,"By means of first principles calculations, we have systematically
investigated how the magnetodynamic properties Gilbert damping, magnetization
and exchange stiffness are affected when permalloy (Py)
(Fe$_{0.19}$Ni$_{0.81}$) is doped with 4d or 5d transition metal impurities. We
find that the trends in the Gilbert damping can be understood from relatively
few basic parameters such as the density of states at the Fermi level, the
spin-orbit coupling and the impurity concentration. % The temperature
dependence of the Gilbert damping is found to be very weak which we relate to
the lack of intraband transitions in alloys. % Doping with $4d$ elements has no
major impact on the studied Gilbert damping, apart from diluting the host.
However, the $5d$ elements have a profound effect on the damping and allows it
to be tuned over a large interval while maintaining the magnetization and
exchange stiffness. % As regards spin stiffness, doping with early transition
metals results in considerable softening, whereas late transition metals have a
minor impact. % Our result agree well with earlier calculations where
available. In comparison to experiments, the computed Gilbert damping appears
slightly underestimated while the spin stiffness show good general agreement.",1602.06201v2
2018-03-23,Observation of hedgehog skyrmions in sub-100 nm soft magnetic nanodots,"Magnetic skyrmions are nanometric spin textures of outstanding potential for
spintronic applications due to unique features governed by their non-trivial
topology. It is well known that skyrmions of definite chirality are stabilized
by the Dzyaloshinskii-Moriya exchange interaction (DMI) in bulk
non-centrosimmetric materials or ultrathin films with strong spin-orbit
coupling in the interface. In this work, we report on the detection of magnetic
hedgehog-skyrmions at room temperature in confined systems with neither DMI nor
perpendicular magnetic anisotropy. We show that soft magnetic (permalloy)
nanodots are able to host non- chiral hedgehog skyrmions that can be further
stabilized by the magnetic field arising from the Magnetic Force Microscopy
probe. Analytical calculations and micromagnetic simulations confirmed the
existence of metastable N\'eel skyrmions in permalloy nanodots even without
external stimuli in a certain size range. Our work implies the existence of a
new degree of freedom to create and manipulate skyrmions in soft nanodots. The
stabilization of skyrmions in soft magnetic materials opens a possibility to
study the skymion magnetization dynamics otherwise limited due to the large
damping constant coming from the high spin-orbit coupling in materials with
high magnetic anisotropy.",1803.08768v1
2019-02-21,Effects of the removal of Ta capping layer on the magnetization dynamics of Permalloy thin films,"We have investigated the spin wave dynamics of Permalloy (Py) thin films with
and without a Ta capping layer for varying Py thickness (15 nm, 20 nm and 30
nm) using all optical time-resolved magneto-optical Kerr effect measurements.
XPS measurements confirm the oxidation of the originally-prepared samples and
also that the removal of the Ta capping layer is achievable by a few sputtering
cycles. The magnetic field strength dependencies of the spin wave modes with
the variation of the Py film thickness for the samples are studied. We observe
that the presence of the Ta capping layer reduces the precessional frequencies
of the samples while the samples without a Ta capping layer enhance the role of
Py thickness. We also observe that the decay time of spin waves is highly
dependent on the top layer of the samples. The decay time increases with
increasing Py thicknesses for Ta/Py/Ta samples implying that the enhancement of
decay time is caused by the Ta/Py/Ta interfaces. Whereas, for Ta/Py samples the
decay time decreases with increasing Py thickness. The results of this work
extend the knowledge on the magnetization dynamics of Py thin films giving
information on how to resume and even enhance the spin mobility after a
deleterious oxidation process. This can open new scenarios on the building
process and on the maintenance of fast magnetic switching devices.",1902.07832v1
2019-06-03,Layer-dependent spin-orbit torques generated by the centrosymmetric transition metal dichalcogenide $β$-MoTe$_2$,"Single-crystal materials with sufficiently low crystal symmetry and strong
spin-orbit interactions can be used to generate novel forms of spin-orbit
torques on adjacent ferromagnets, such as the out-of-plane antidamping torque
previously observed in WTe$_2$/ferromagnet heterostructures. Here, we present
measurements of spin-orbit torques produced by the low-symmetry material
$\beta$-MoTe$_2$, which unlike WTe$_2$ retains bulk inversion symmetry. We
measure spin-orbit torques on $\beta$-MoTe$_2$/Permalloy heterostructures using
spin-torque ferromagnetic resonance as a function of crystallographic alignment
and MoTe$_2$ thickness down to the monolayer limit. We observe an out-of-plane
antidamping torque with a spin torque conductivity as strong as 1/3 of that of
WTe$_2$, demonstrating that the breaking of bulk inversion symmetry in the
spin-generation material is not a necessary requirement for producing an
out-of-plane antidamping torque. We also measure an unexpected dependence on
the thickness of the $\beta$-MoTe$_2$ -- the out-of-plane antidamping torque is
present in MoTe$_2$/Permalloy heterostructures when the $\beta$-MoTe$_2$ is a
monolayer or trilayer thick, but goes to zero for devices with bilayer
$\beta$-MoTe$_2$.",1906.01068v1
2017-10-19,Spin-triplet supercurrent in Josephson junctions containing a synthetic antiferromagnet with perpendicular magnetic anisotropy,"We present measurements of Josephson junctions containing three magnetic
layers with noncolinear magnetizations. The junctions are of the form
$S/F^{\prime}/N/F/N/F^{\prime \prime}/S$, where $S$ is superconducting Nb,
$F^\prime$ is either a thin Ni or Permalloy layer with in-plane magnetization,
$N$ is the normal metal Cu, $F$ is a synthetic antiferromagnet (SAF) with
magnetization perpendicular to the plane, composed of Pd/Co multilayers on
either side of a thin Ru spacer, and $F^{\prime \prime}$ is a thin Ni layer
with in-plane magnetization. The supercurrent in these junctions decays more
slowly as a function of the $F$-layer thickness than for similar spin-singlet
junctions not containing the $F^\prime$ and $F^{\prime \prime}$ layers. The
slower decay is the prime signature that the supercurrent in the central part
of these junctions is carried by spin-triplet pairs. The junctions containing
$F^{\prime}=$ Permalloy are suitable for future experiments where either the
amplitude of the critical current or the ground-state phase difference across
the junction is controlled by changing the relative orientations of the
magnetizations of the $F^{\prime}$ and $F^{\prime \prime}$ layers.",1710.07247v1
2021-04-16,Target domains in nanometric Permalloy disks with columnar structure,"We conducted a thorough experimental and numerical study of the micromagnetic
properties of Permalloy (Ni$_{80}$Fe$_{20}$) microdisks exhibiting target
domain structures at remanence. Vortex configurations are quite common in such
microdisks and correspond to an in-plane flux closure configuration of
cylindrical symmetry with an out-of-plane magnetized core. In contrast, target
domain configuration are observed in thicker microdisks and are characterized
by a vortex configuration of the in-plane component of the magnetization
superposed to an out-of-plane component of magnetization which oscillates as a
function of the distance to the microdisk center resulting in the formation of
concentric domains. The ratio of the out-of-plane oscillatory component of the
magnetization to the in-plane vortex one increases with the thickness of the
microdisk. Hysteresis loops were measured under in-plane and out-of-plane
field. The results at remanence and under magnetic field could be interpreted
by micromagnetic simulations in which the microdisks were described as an
assembly of partially coupled columns representing the granular nanostructure
of the films from which the microdisks were patterned. Quite original
magnetization processes take place in these microdisks exhibiting target domain
remanent configuration. These include in particular entire flipping of the
domain configuration and annihilation/creation of ring domains.",2104.07946v1
2019-01-26,Effects of Nanodots Shape and Lattice Constants on the Spin Wave Dynamics of Patterned Permalloy Dots,"Micromagnetic simulations studies on Permalloy (Ni80Fe20) nanodot with
different shape and edge-to-edge separation (s) down to 25nm arranged in square
lattice are reported. We observe the significant variation of spin-wave (SW)
dynamics of nanodots of different shapes (triangular, diamond and hexagon) and
of fixed dot diameter 100nm with varying s. Modes for single dot are
transformed in an array into multiple quantized, edge and centre modes for
different shapes and edge-to-edge separations, with different spin wave
frequencies and peak intensities. Specifically, in the triangular dot sample, a
broad range of mode frequencies is observed with highest SW frequency 14.7 GHz.
For separation less than 100nm, the SW frequencies undergoes significant
modification due to the varying nature of the magnetostatic and dipolar
interaction in the array while for separation above 100nm, the SW frequency
mostly remain constant. The power profiles confirm the nature of the observed
modes. The spatial profiles of magnetostatic field are determined by a
combination of internal magnetic-field profiles within the nanodots and the
magnetostatic fields within the lattice. The inter-dots interaction of
magnetostatic field shows dipolar and quadrupole contributions for all the
shapes. Interestingly, vortex states with shifted core and polarity are
observed in the array for all the shapes at Hbias = 0. Our results provide
important understanding about the tunability of SW spectra in the array of
triangular, diamond and hexagon shaped nanoelements.",1901.09155v1
2019-07-03,Chiral asymmetry detected in a 2D array of permalloy square nanomagnets using circularly polarized X ray Resonant Magnetic Scattering,"The sensitivity of Circularly polarized X ray Resonant Magnetic Scattering
(CXRMS) to chiral asymmetry has been demonstrated. The study was performed on a
2D array of Permalloy (Py) square nanomagnets of 700 nm lateral size arranged
in a chess lattice of 1000 nm lattice parameter. Previous X ray Magnetic
Circular Dichroism Photoemission Electron microscopy (XMCD-PEEM) images on this
sample showed the formation of vortices at remanence and a preference in their
chiral state. The magnetic hysteresis loops of the array along the diagonal
axis of the squares indicate a non-negligible and anisotropic interaction
between vortices. The intensity of the magnetic scattering using circularly
polarized light along one of the diagonal axes of the square magnets becomes
asymmetric in intensity in the direction transversal to the incident plane at
fields where the vortex states are formed. The asymmetry sign is inverted when
the direction of the applied magnetic field is inverted. The result is the
expected in the presence of an unbalanced chiral distribution. The effect is
observed by CXRMS due to the interference between the charge scattering and the
magnetic scattering.",1907.02016v2
2020-12-16,A tool to predict coercivity in magnetic materials,"Magnetic coercivity is often viewed to be lower in alloys with negligible (or
zero) values of the anisotropy constant. However, this explains little about
the dramatic drop in coercivity in FeNi alloys at a non-zero anisotropy value.
Here, we develop a theoretical and computational tool to investigate the
fundamental interplay between material constants that govern coercivity in bulk
magnetic alloys. The two distinguishing features of our coercivity tool are
that: (a) we introduce a large localized disturbance, such as a spike-like
magnetic domain, that provides a nucleation barrier for magnetization reversal;
and (b) we account for magneto-elastic energy -- however small -- in addition
to the anisotropy and magnetostatic energy terms. We apply this coercivity tool
to show that the interactions between local instabilities and material
constants, such as anisotropy and magnetostriction constants, are key factors
that govern magnetic coercivity in bulk alloys. Using our model, we show that
coercivity is minimum at the permalloy composition (Fe-21.5Ni-78.5) at which
the alloy's anisotropy constant is not zero. We systematically vary the values
of the anisotropy and magnetostriction constants, around the permalloy
composition, and identify new combinations of material constants at which
coercivity is small. More broadly, our coercivity tool provides a theoretical
framework to potentially discover novel magnetic materials with low coercivity.",2012.09320v1
2021-07-05,Inverse magnetic hysteresis of the Josephson supercurrent: study of the magnetic properties of thin niobium/permalloy (Fe_{20}Ni_{80}) interfaces,"We propose a picture for the magnetic properties of
superconductor/ferromagnet (S/F) heterostructures based on Nb and permalloy
(Py: Fe_{20}Ni_{80}). By measuring the magnetic moment as a function of the
temperature in S/F/S trilayers for different thicknesses of the middle F layer,
we give evidence of the presence of a magnetic stray field of the F layer. For
values of F-layer thickness below a threshold, we establish a correlation
between the magnetic measurements of the S/F/S trilayers and the anomalous
magnetic dependence of the critical current in S/insulator/thin superconducting
film/F/S (SIsFS) Josephson junctions (JJs). These complementary investigations
provide a self-consistent method to fully characterize S/F heterostructures and
possibly demonstrate effects arising from the mutual interactions between
ferromagnetism and superconductivity. A shift in the Fraunhofer critical
current oscillations has been observed in the opposite direction to the one
commonly observed in JJs with F barriers, as it has been recently predicted by
inverse and electromagnetic proximity theories. This inverse memory effect is
relevant for the design of these heterostructures as memory cells and
spintronic devices.",2107.02142v1
2022-05-02,High-Sensitivity Characterization of Ultra-Thin Atomic Layers using Spin-Hall Effect of Light,"Magnetic/non-magnetic/heterostructured ultra-thin films' characterisation is
highly demanding due to the emerging diverse applications of such films.
Diverse measurements are usually performed on such systems to infer their
electrical, optical and magnetic properties. We demonstrate that MOKE-based
spin-Hall effect of light (SHEL) is a versatile surface characterization tool
for studying materials' magnetic and dielectric ordering. Using this technique,
we measure magnetic field dependent complex Kerr angle and the coercivity in
ultra-thin films of permalloy (Py) and at molybdenum disulphide (MoS$_2$) -
permalloy (MSPy) hetero-structure interfaces. The measurements are compared
with standard magneto-optic Kerr effect (MOKE) studies to demonstrate that
SHEL-MOKE is a practical alternative to the conventional MOKE method, with
competitive sensitivity. A comprehensive theoretical model and simulation data
are provided to further strengthen the potential of this simple non-invasive
optical method. The theoretical model is applied to extract the optical
conductivity and susceptibility of non-magnetic ultra-thin layers such as
MoS$_2$ .",2205.00660v2
2022-06-06,Topological magnetic dipoles and emergent field bundles in a ferromagnetic microstructure by X-ray magnetic vector tomography,"Advanced vector imaging techniques provide us with 3D maps of magnetization
fields in which topological concepts can be directly applied to describe
real-space experimental textures in non-ideal geometries. Here, the 3D
magnetization of a low symmetry permalloy microstructure is obtained by X-ray
vector magnetic tomography and analysed in detail in terms of topological
charges and emergent fields. A central asymmetric domain wall with a complex 3D
structure is observed in which magnetization chirality transitions are mediated
by Bloch points arranged in several dipoles and a triplet. The ideal spherical
symmetry of the emergent field of an isolated monopole is severely modified due
to shape effects of the permalloy microstructure. Emergent field lines
aggregate into bundles that either connect adjacent Bloch points within a
topological dipole or tend towards the surface. These bundles may present
different textures such as helical vortices or half merons, depending on
asymmetries and confinement, but are constrained by topological charge
conservation in a given sample volume. This precise description of the
singularities in realistic systems, enabled by the quantitative experimental
information on magnetization vector fields, can significantly improve our
understanding of topological constraints in 3D magnetic systems and provide
advancements in the design of magnetic devices.",2206.02499v1
2022-12-24,Spin-to-charge conversion by spin pumping in sputtered polycrystalline Bi$_x$Se$_{1-x}$,"Topological materials are of high interest due to the promise to obtain low
power and fast memory devices based on efficient spin-orbit torque switching or
spin-orbit magnetic state read-out. In particular, sputtered polycrystalline
Bi$_x$Se$_{1-x}$ is one of the materials with more potential for this purpose
since it is relatively easy to fabricate and has been reported to have a very
high spin Hall angle. We study the spin-to-charge conversion in
Bi$_x$Se$_{1-x}$ using the spin pumping technique coming from the ferromagnetic
resonance in a contiguous permalloy thin film. We put a special emphasis on the
interfacial properties of the system. Our results show that the spin Hall angle
of Bi$_x$Se$_{1-x}$ has an opposite sign to the one of Pt. The charge current
arising from the spin-to-charge conversion is, in contrast, lower than Pt by
more than one order of magnitude. We ascribe this to the interdiffusion of
Bi$_x$Se$_{1-x}$ and permalloy and the changes in chemical composition produced
by this effect, which is an intrinsic characteristic of the system and is not
considered in many other studies.",2212.12697v2
2023-02-01,A Brillouin light scattering study of the spin-wave magnetic field dependence in a magnetic hybrid system made of an artificial spin-ice structure and a film underlayer,"We present a combined Brillouin light scattering and micromagnetic simulation
investigation of the magnetic-field dependent spin-wave spectra in a hybrid
structure made of permalloy (NiFe) artificial spin-ice (ASI) systems, composed
of stadium-shaped nanoislands, deposited on the top of an unpatterned permalloy
film with a nonmagnetic spacer layer. The thermal spin-wave spectra were
recorded by Brillouin light scattering (BLS) as a function of the magnetic
field applied along the symmetry direction of the ASI sample. Magneto-optic
Kerr effect magnetometry was used to measure the hysteresis loops in the same
orientation as the BLS measurements. The frequency and intensity of several
spin-wave modes detected by BLS were measured as a function of the applied
magnetic field. Micromagnetic simulations enabled us to identify the modes in
terms of their frequency and spatial symmetry and to extract information about
the existence and strength of the dynamic coupling, relevant only to a few
modes of a given hybrid system. Using this approach, we suggest a way to
understand if dynamic coupling between ASI and film modes is present or not,
with interesting implications for the development of future three-dimensional
magnonic applications and devices.",2302.00483v1
2024-02-07,Anatomy of localized edge modes in laterally coupled waveguides,"We present a systematic micromagnetic study of standing spin-wave modes in
infinitely long Permalloy strips with rectangular cross-section. Using a
finite-element dynamic-matrix method, we first calculate the eigenfrequencies
and the corresponding eigenvectors (mode profiles), as a function of the
in-plane magnetic field applied across the strip. The ferromagnetic resonance
spectra is computed from the mode profiles, assuming a homogeneous
radio-frequency excitation, equivalently to an experimental ferromagnetic
resonance measurement. The investigation of the field-dependent mode profiles
enables for the classification of the observed resonances, here focusing mostly
on the true edge mode localized at the vicinity of strip edges. Furthermore, we
study the mode localization in pairs of 50-nm-thick Permalloy strips as a
function of the strip width and their lateral separation. For closely spaced
strips, the spatial profile of the quasi-uniform mode is substantially modified
due to a significant hybridization with the edge-localized standing spin-wave
modes of the neighbouring strip. We show that a wide-range-tunability of the
localized edge-mode resonances can be achieved with a precise control of the
magnetostatic coupling between the strips. Extreme sensitivity of the edge mode
frequency on the bias field demonstrates a potential of the edge resonances for
field sensing. Furthermore, for narrow strips (~100 nm in width), due to the
reduced number of the allowed confined modes, a field-controllable switching
between the resonances localized either in the strip center or at the edges of
the strips can be achieved.",2402.04715v1
2024-02-15,Standing spin waves in Permalloy-NiO bilayers as a probe of the interfacial exchange coupling,"Ferromagnetic/Antiferromagnetic (FM/AFM) bilayers dynamics have been a recent
topic of interest due to the interaction occurring at the interface, where the
magnetic moments of the AFM can be imprinted into the FM, and the exchange bias
field can affect these dynamics. Here, we investigate Permalloy (Py) and NiO
(Py/NiO) hybrids and for comparison single Py films in the broad Py thickness
range varied from few nm to 200 nm by using static (Kerr effect) and dynamic
(spin waves) measurements along with micromagnetic simulations. We observe
hybrid modes between uniform (ferromagnetic resonance FMR, n=0) and
perpendicular standing spin waves (PSSWs, n=1, 2) and a clear enhancement of
the PSSWs modes frequencies upon interfacing Py with NiO both from experiments
and simulations. This enhancement becomes less pronounced as the thickness of
the film increases, demonstrating its interfacial origin rooted in the exchange
coupling between the FM and AFM layers. Besides, through micromagnetic
simulations, we investigate and correlate changes in spatial profiles of the
PSSWs with the interfacial exchange coupling. As the thickness is increased, we
see that the n=1 and n=2 modes begin to couple with the fundamental FMR mode,
resulting in asymmetric (with respect the Py layer center) modes. Our results
suggest that PSSWs detection in a ferromagnet offers a means of probing the
interfacial exchange coupling with the adjacent AFM layer. Furthermore, the
controlled spatial symmetry breaking by the AFM layer enables engineering of
PSSWs with different spatial profiles in the FM.",2402.10292v1
2011-11-16,Review and Analysis of Measurements of the Spin Hall Effect in Platinum,"Several different experimental techniques have been used in efforts to
measure the spin Hall conductivity and the spin Hall angle in Pt samples at
room temperature, with results that disagree by more than a factor of 20, with
spin Hall conductivities from 2.4 x 10^4 to 5.1 x 10^5 [hbar/(2e)] (Ohm-m)^-1
and spin Hall angles from 0.0037 to 0.08. We review this work, and analyze
possible reasons for the discrepancies. We explain that the smallest values for
the spin Hall angle that have been reported, based on measurements of lateral
permalloy/copper/platinum devices, are incorrect because the original analyses
did not properly take into account that copper layers in these devices will
shunt charge current flowing through adjacent platinum wires, thereby greatly
reducing the size of the spin-Hall-related signals. We suggest that differences
between the results for the spin Hall angle found by other experimental
techniques are primarily a consequence of different assumptions about the value
of the spin diffusion length in Pt. We present a new measurement of the spin
diffusion length in Pt within sputtered Pt/permalloy bilayer thin films at room
temperature, finding 1.4 \pm 0.3 nm, a much smaller value than has generally
been assumed previously. With this value for the spin diffusion length, the
previously-discordant results can be brought into much better agreement, with
the result that the spin Hall conductivities are (1.4 - 3.4) x 10^5 [hbar/(2e)]
(Ohm-m)^-1 and the spin Hall angles are greater than 0.05. These values are
sufficiently large that the spin Hall effect in Pt can be used to generate spin
currents and spin transfer torques strong enough for efficient manipulation of
magnetic moments in adjacent ferromagnetic layers.",1111.3702v3
2015-03-13,Paper-based spintronics: magneto-resistivity of permalloy deposited onto paper substrates,"Driven by low-cost, resource abundance and distinct material properties, the
use of paper in electronics, optics and fluidics is under investigation.
Considering sensor systems based on magneto-resistance principles (anisotropic,
giant, tunnel) that are conventionally manufactured onto inorganic
semiconductor materials, we propose the use of paper substrates for cost
reduction purposes primarily. In particular, we studied the magneto-resistance
sensitivity of permalloy (Py:Ni81Fe19) onto paper substrates. In this work, we
report on our findings with clean room paper (80 g/m2, Rrms = 2.877 {\mu}m, 23%
surface porosity, latex impregnation, no embossed macro-structure). Here, the
Py:Ni81Fe19 coating was manufactured by means of a dry process, sputter
deposition, and spans an area of 10x10 mm2 and a thickness of 70 nm. Employing
a four-point-probe DC resistivity measurement setup, we investigated the change
of electrical resistance of Py:Ni81Fe19 under the presence of an oriented
external magnetic field. In particular, we investigate the magneto-resistive
change at two configurations: (1) the direction of the magnetic field is
parallel to the nominal induced electric current and (2) the direction of the
magnetic field is perpendicular to the electric current. Due to the stochastic
orientation of the fibers interplaying with the Py:Ni81Fe19 coating, the change
in magneto-resistance of the overall system at both measurement configurations
closely corresponds to the classical response of Py:Ni81Fe19 at a +/-45{\deg}
angle between the direction of electrical current and magnetic field. Using the
magneto-optic kerr effect, we observed the formation of domain walls at the
fiber bending locations. Future work will focus on the impact of layer
thickness, fiber dimensions and structure of magnetic coating on the
performance of the paper-based Py:Ni81Fe19 magneto-resistors.",1503.04853v2
2015-08-08,Direct comparison of domain wall behavior in Permalloy nanowires patterned by electron beam lithography and focused ion beam milling,"Nominally identical permalloy nanowires, with widths down to 150 nm, were
fabricated onto a single electron transparent Si$_{3}$N$_{4}$ membrane using
electron beam lithography (EBL) and focused ion beam (FIB) milling.
Transmission electron microscopy (TEM) experiments were performed to compare
the nanostructures produced by these two techniques in what we believe is the
first direct comparison of fabrication techniques for nominally identical
nanowires. Both EBL and FIB methods produced high quality structures with edge
roughness being of the order of the mean grain size 5 -10 nm observed in the
continuous films. However, significant grain growth was observed along the
edges of the FIB patterned nanowires. Lorentz TEM \emph{in situ} imaging was
carried out to compare the magnetic behavior of the domain walls in the
patterned nanowires with anti-notches present to pin domain walls. The overall
process of domain wall pinning and depinning at the anti-notches showed
consistent behaviour between nanowires fabricated by the two methods with the
FIB structures having slightly lower characteristic fields compared to the EBL
wires. However, a significant difference was observed in the formation of a
vortex structure inside the anti-notches of the EBL nanowires after depinning
of the domain walls. No vortex structure was seen inside the anti-notches of
the FIB patterned nanowires. Results from micromagnetic simulations suggest
that the vortex structure inside the anti-notch can be suppressed if the
saturation magnetization (M$_{s}$) is reduced along the nanowires edges. Whilst
the two fabrication methods show that well defined structures can be produced
for the dimensions considered here, the differences in the magnetic behavior
for nominally identical structures may be an issue if such structures are to be
used as conduits for domain walls in potential memory and logic applications.",1508.01910v1
2016-04-27,Collective spin excitations in bi-component magnonic crystals consisting of bi-layer Permalloy/Fe nanowires,"In the developing field of magnonics,it is very important to achieve
tailoring of spin wave propagation by both a proper combination of materials
with different magnetic properties and their nanostructuring on the
submicrometric scale. We have exploited deep ultra-violet lithography, in
combination with tilted shadow deposition technique, to fabricate arrays of
closely spaced bi-layer nanowires (NWs), with separation d=100 nm and
periodicity a=440 nm, having bottom and top layers made of Permalloy and Iron,
respectively. The NWs have either rectangular cross section (bottom and upper
layers of equal width) or L-shaped cross section (upper layer of half width).
The frequency dispersion of collective spin wave excitations in the above
bi-layered NWs arrays has been measured by the Brillouin light scattering
technique while sweeping the wave vector perpendicularly to the wire length
over three Brillouin zones of the reciprocal space. For the rectangular NWs,
the lowest frequency fundamental mode, characterized by a quasi- uniform
profile of the amplitude of the dynamic magnetization across the NW width,
exhibits a sizeable and periodic frequency dispersion. A similar dispersive
mode is also present in L-shaped NWs, but the mode amplitude is concentrated in
the thin side of the NWs. The width and the center frequency of the magnonic
band associated with the above fundamental modes has been analyzed, showing
that both can be tuned by varying the external applied field. Moreover, for the
L-shaped NWs it is shown that there is also a second dispersive mode,at higher
frequency,characterized by an amplitude concentrated in the thick side of the
NW. These experimental results have been quantitatively reproduced by an
original numerical model that includes two-dimensional Green's function of the
dipole field of the dynamic magnetization and interlayer exchange coupling
between the layers.",1604.07950v1
2020-10-13,Tailoring interface mixing and magnetic properties in (111) Permalloy/Pt multilayers,"We present deposition and characterization of multilayers consisting of 20
repetitions of 15 $\r{A}$ thick permalloy Ni$_{80}$Fe$_{20}$ at. \% (Py) and 5
$\r{A}$ Pt. The samples were prepared by two different sputter deposition
methods, namely dc magnetron sputtering (dcMS) and high power impulse magnetron
sputtering (HiPIMS), that represent low and moderate ionized flux fraction of
the film forming material, respectively, for deposition of the Py layers. The
effect of substrate roughness, working gas pressure and sputter power on the
in-plane uniaxial magnetic anisotropy of the films are studied. The multilayers
were characterized by X-ray reflectivity and diffraction, and by
magneto-optical Kerr effect (MOKE). It is shown that HiPIMS deposition produces
multilayers with unique surface roughness regardless of the substrate surface
roughness. Multilayers prepared by both dcMS and HiPIMS deposition present a
strong (111) texture normal to the film plane. The results show that utilizing
HiPIMS for deposition of the Py layer leads to a minimum interface mixing
between individual layers compared to dcMS deposition performed at sputter
power. This is associated with the smooth surface of Py deposited by HiPIMS.
However, this sharp interface results in higher coercivity and an opening in
the hard axis hysteresis loops while multilayers with intermixing present well
defined in-plane uniaxial anisotropy i.e. a linear hard axis. Comparison with
Py/Cu and Py/CuPt multilayers, prepared under identical conditions using
HiPIMS, suggests that poor in-plane uniaxial anisotropy is obtained in the
Py/Pt case, caused by the inverse magnetostriction arising from the large
lattice mismatch between Py and Pt. The Py/Pt multilayers that exhibit
interface mixing have a more relaxed interface and thus presents negligible
inverse magnetostriction and have better defined anisotropy.",2010.06104v3
1999-02-03,An observation of spin-valve effects in a semiconductor field effect transistor: a novel spintronic device,"We present the first spintronic semiconductor field effect transistor.
  The injector and collector contacts of this device were made from magnetic
permalloy thin films with different coercive fields so that they could be
magnetized either parallel or antiparallel to each other in different applied
magnetic fields. The conducting medium was a two dimensional electron gas
(2DEG) formed in an AlSb/InAs quantum well.
  Data from this device suggest that its resistance is controlled by two
different types of spin-valve effect: the first occurring at the
ferromagnet-2DEG interfaces; and the second occuring in direct propagation
between contacts.",9902057v1
1999-02-16,Dependence of Magnetic Anisotropy and Magnetoresistance of Ni81Fe19-Films on Annealing,"Permalloy (Py:Ni81Fe19) exhibits an anisotropic magnetoresistance (AMR) which
is very often used to read magnetic signals from storage devices. Py-films of
thickness 20nm were prepared by dc-magnetron sputtering in a magnetic field
onto thermally oxidized Si-wafers and annealed ex situ at temperatures up to
1000K in order to investigate the dependence of the magnetic anisotropy and the
AMR on heat treatments. The films exhibit an uniaxial anisotropy after
preparation which changes during annealing above 520K. The AMR along the former
magnetically easy axis as well as the corresponding field sensitivity are
increased by a heat treatment around 700K reaching maxima of about 8% and a
maximum sensitivity of 1.5%/Oe, respectively. We discuss possible sources for
the change in anisotropy, i.e. strain effects, inhomogeneities, and changes of
the local atomic order.",9902222v1
2000-01-13,Ab-initio Theoretical Description of the Interrelation between Magnetocrystalline Anisotropy and Atomic Short-Range Order,"The cubic lattice symmetry of ferromagnetic homogeneously disordered alloys
is when a compositional modulation is imposed. This can have a profound
influence on the magnetocrystalline anisotropy energy (MAE). We describe our
ab-initio theory of this effect and use the framework of concentration waves
with the electronic structure described within the spin-polarised relativistic
Korringa-Kohn-Rostoker coherent-potential approximation. We find that ordering
produces a 2 order of magnitude increase in the MAE as well as altering the
equilibrium direction of magnetisation. Using the same theoretical framework we
also examine directional compositional order produced by magnetic annealing
with an explicit study of permalloy.",0001181v1
2000-07-19,Electrical spin injection and detection in a semiconductor. Is it feasible?,"The electrical injection of spin polarized electrons in a semiconductor can
be achieved in principle by driving a current from a ferromagnetic metal, where
current is known to be significantly spin polarized, into the semiconductor via
ohmic conduction. For detection a second ferromagnet can be used as drain. We
studied submicron lateral spin valve junctions, based on high mobility
InAs/AlSb two-dimensional electron gas (2DEG), with Ni, Co and Permalloy as
ferromagnetic electrodes. In the standard geometry it is very difficult to
separate true spin injection from other effects, including local Hall effect,
anomalous magnetoresistance (AMR) contribution from the ferromagnetic
electrodes and weak localization/anti-localization corrections, which can
closely mimic the signal expected from spin valve effect. The reduction in
size, and the use of a multiterminal non-local geometry allowed us to reduce
the unwanted effects to a minimum. Despite all our efforts, we have not been
able to observe spin injection. However, we find that this 'negative' result in
these systems is actually consistent with theoretical predictions for spin
transport in diffusive systems.",0007307v1
2001-04-23,Interacting circular nanomagnets,"Regular 2D rectangular lattices of permalloy nanoparticles (40 nm in
diameter) were prepared by the method of the electron lithography. The
magnetization curves were studied by Hall magnetometry with the compensation
technique for different external field orientations at 4.2K and 77K. The shape
of hysteresis curves indicates that there is magnetostatic interaction between
the particles. The main peculiarity is the existence of remanent magnetization
perpendicular to easy plain. By numerical simulation it is shown, that the
character of the magnetization reversal is a result of the interplay of the
interparticle interaction and the magnetization distribution within the
particles (vortex or uniform).",0104421v2
2002-08-12,The role of electron scattering in magnetization relaxation in thin Ni$_{81}$Fe$_{19}$ films,"We observe a strong correlation between magnetization relaxation and
electrical resistivity in thin Permalloy (Ni$_{81}$Fe$_{19}$, ``Py'') films.
Electron scattering rates in the films were affected by varying film thickness
and deposition conditions. This shows that the magnetization relaxation
mechanism is analogous to ``bulk'' relaxation, where phonon scattering in bulk
is replaced by surface and defect scattering in thin films. Another interesting
finding is the increased magnetization damping with Pt layers adjacent to the
Py films. This is attributed to the strong spin-orbit coupling in Pt, resulting
in spin-flip scattering of electrons that enter from the Py.",0208207v1
2002-10-06,Measuring Lateral Magnetic Structure in Thin Films Using Polarized Neutron Reflectometry,"Polarized neutron reflectometry (PNR) has long been applied to measure the
magnetic depth profile of thin films. In recent years, interest has increased
in observing lateral magnetic structures in a film. While magnetic arrays
patterned by lithography and submicron-sized magnetic domains in thin films
often give rise to off-specular reflections, micron-sized ferromagnetic domains
on a thin film produce few off-specular reflections and the domain distribution
information is contained within the specular reflection. In this paper, we will
first present some preliminary results of off-specular reflectivity from arrays
of micron-sized permalloy rectangular bars. We will then use specular
reflections to study the domain dispersion of an exchange-biased Co/CoO bilayer
at different locations of the hysteresis loop.",0210124v1
2003-03-08,Current-Driven Magnetic Excitations in Permalloy-Based Multilayer Nanopillars,"We study current-driven magnetization switching in nanofabricated
Ni84Fe16/Cu/Ni84Fe16 trilayers at 295 K and 4.2 K. The shape of the hysteretic
switching diagram at low magnetic field changes from 295 K to 4.2 K. The
reversible behavior at higher field involves two phenomena, a threshold current
for magnetic excitations closely correlated with the switching current, and a
peak in differential resistance characterized by telegraph noise, with average
period that decreases exponentially with current and shifts with temperature.
We interpret both static and dynamic results at 295 K and 4.2 K in terms of
thermal activation over a potential barrier, with a current dependent effective
magnetic temperature.",0303149v2
2003-09-18,Controllable Josephson current through a pseudo-spin-valve structure,"A thin Co/Cu/Permalloy (Ni$_{80}$Fe$_{20}$) pseudo-spin-valve structure is
sandwiched between superconducting Nb contacts. When the current is passed
perpendicular to the plane of the film a Josephson critical current ($I_C$) is
observed at 4.2 K, in addition to a magnetoresistance (MR) of $\sim$ 0.5 % at
high bias. The hysteresis loop of the spin-valve structure can be cycled to
modulate the zero field $I_C$ of the junction in line with the MR measurements.
These modulations of resistance and $I_C$ occur both smoothly and sharply with
the applied field. For each type of behaviour there is a strong correlation
between shape of the MR loops and the $I_C$ modulation.",0309430v1
2003-09-29,Extraction of domain-specific magnetization reversal for nanofabricated periodic arrays using soft x-ray resonant magnetic scattering,"A simple scheme to extract the magnetization reversals of characteristic
magnetic domains on nanofabricated periodic arrays from soft x-ray resonant
magnetic scattering (SXRMS) data is presented. The SXRMS peak intensities from
a permalloy square ring array were measured with field cycling using circularly
polarized soft x-rays at the Ni L$_3$ absorption edge. Various SXRMS hysteresis
loops observed at different diffraction orders enabled the determination of the
magnetization reversal of each magnetic domain using a simple linear algebra.
The extracted domain-specific hysteresis loops reveal that the magnetization of
the domain parallel to the field is strongly pinned, while that of the
perpendicular domain rotates continuously.",0309672v1
2003-11-25,Measuring Magnetostriction with an Atomic Force Microscope: Application to Wires in Ballistic Magnetoresistance,"In this study we present a new method of measuring magnetostriction with an
atomic force microscope adapted for the application magnetic fields. The
experiment allows us to visualise, in an elegant and educational way how the
lateral magnetoelastic shape changes take place on the sample surface when a
magnetic field is applied. We have, furthermore, used this technique to observe
magnetically induced strains as small as 5*10-8, and have measured Ni,
permalloy and commercial Cu wires and films, as well as pure Cu and Pt wires,
where results are in agreement with other methods of measurement. The
applications are, moreover, relevant to studies of ballistic magnetoresistance,
where we can draw conclusions involving the effect of the magnetically induced
strains on magnetoresistance measured at the same time as magnestostriction.",0311567v1
2004-03-29,Enhancement of the superconducting transition temperature in Nb/Permalloy bilayers by controlling the domain state of the ferromagnet,"In (S/F) hybrids the suppression of superconductivity by the exchange field
h_ex of the ferromagnet can be partially lifted when different directions of
h_ex are sampled simultaneously by the Cooper pair. In F/S/F trilayer
geometries where the magnetization directions of the two F-layers can be
controlled separately, this leads to the so-called spin switch. Here we show
that domain walls in a single F-layer yield a similar effect. We study the
transport properties of Ni_0.8Fe_0.2/Nb bilayers structured in strips of
different sizes. For large samples a clear enhancement of superconductivity
takes place in the resistive transition, in the very narrow field range (order
of 0.5 mT) where the magnetization of the Py layer switches and many domains
are present. This effect is absent in microstructured samples. Comparison of
domain wall width \delta_w to the temperature dependent superconductor
coherence length \xi_S(T) shows that \delta_w ~ \xi_S(T), which means that the
Cooper pairs sample a large range of different magnetization directions.",0403697v1
2004-10-09,Current distribution inside Py/Cu lateral spin-valve device,"We have investigated experimentally the non-local voltage signal (NLVS) in
the lateral permalloy (Py)/Cu/Py spin valve devices with different width of Cu
stripes. We found that NLVS strongly depends on the distribution of the
spin-polarized current inside Cu strip in the vicinity of the Py-detector. To
explain these data we have developed a diffusion model describing spatial (3D)
distribution of the spin-polarized current in the device. The results of our
calculations show that NLVS is decreased by factor of 10 due to spin
flip-scattering occurring at Py/Cu interface. The interface resistivity on
Py/Cu interface is also present, but its contribution to reduction of NLVS is
minor. We also found that most of the spin-polarized current is injected within
the region 30 nm from Py-injector/Cu interface. In the area at Py-detector/Cu
interface, the spin-polarized current is found to flow mainly close on the
injector side, with 1/e exponential decay in the magnitude within the distance
80 nm.",0410228v1
2005-08-30,Large angle magnetization dynamics measured by time-resolved ferromagnetic resonance,"A time-resolved ferromagnetic resonance technique was used to investigate the
magnetization dynamics of a 10 nm thin Permalloy film. The experiment consisted
of a sequence of magnetic field pulses at a repetition rate equal to the
magnetic systems resonance frequency. We compared data obtained by this
technique with conventional pulsed inductive microwave magnetometry. The
results for damping and frequency response obtained by these two different
methods coincide in the limit of a small angle excitation. However, when
applying large amplitude field pulses, the magnetization had a non-linear
response. We speculate that one possible cause of the nonlinearity is related
to self-amplification of incoherence, known as the Suhl instabilities.",0508708v1
2005-09-06,Inverse spin switch effects in Ferromagnet / Superconductor hybrids with strong ferromagnets,"In F/S/F trilayers where the magnetization directions of the F layers can be
controlled separately, it has theoretically been predicted that the
antiparallel (AP) configuration can have a higher superconducting transition
temperature T_c than the parallel configuration. This is the so-called spin
switch, which also experimentally has been found for the case of weak
ferromagnets. Here we show that strong ferromagnets yield the opposite effect.
We study the transport properties of F/S/F trilayers with F = Ni_0.80Fe_0.20
(Permalloy, Py) and S = Nb, structured in strips of different sizes. Using two
different thicknesses for the Py layers, we can switch in a well-defined way
between the AP- and P-configurations. In the superconducting transition we find
a clear increase of the resistance in the AP-state. We ascribe this to enhanced
reflection of spin-polarized quasiparticles at the S/F interfaces which leads
to a stronger suppression of superconductivity on the S-side.",0509156v1
2005-10-31,Time-Resolved Spin Torque Switching and Enhanced Damping in Py/Cu/Py Spin-Valve Nanopillars,"We report time-resolved measurements of current-induced reversal of a free
magnetic layer in Py/Cu/Py elliptical nanopillars at temperatures T = 4.2 K to
160 K. Comparison of the data to Landau-Lifshitz-Gilbert macrospin simulations
of the free layer switching yields numerical values for the spin torque and the
Gilbert damping parameters as functions of T. The damping is strongly
T-dependent, which we attribute to the antiferromagnetic pinning behavior of a
thin permalloy oxide layer around the perimeter of the free layer. This
adventitious antiferromagnetic pinning layer can have a major impact on spin
torque phenomena.",0510798v2
2006-02-09,Anisotropic magnetoresistance and anisotropic tunneling magnetoresistance due to quantum interference in ferromagnetic metal break junctions,"We measure the low-temperature resistance of permalloy break junctions as a
function of contact size and the magnetic field angle, in applied fields large
enough to saturate the magnetization. For both nanometer-scale metallic
contacts and tunneling devices we observe large changes in resistance with
angle, as large as 25% in the tunneling regime. The pattern of
magnetoresistance is sensitive to changes in bias on a scale of a few mV. We
interpret the effect as a consequence of conductance fluctuations due to
quantum interference.",0602251v2
2006-02-19,Origin of four-fold anisotropy in square lattices of circular ferromagnetic dots,"We discuss the four-fold anisotropy of in-plane ferromagnetic resonance (FMR)
field $H_r$, found in a square lattice of circular Permalloy dots when the
interdot distance $a$ gets comparable to the dot diameter $d$. The minimum
$H_r$, along the lattice $<11>$ axes, and the maximum, along the $<10>$ axes,
differ by $\sim$ 50 Oe at $a/d$ = 1.1. This anisotropy, not expected in
uniformly magnetized dots, is explained by a non-uniform magnetization
$\bm(\br)$ in a dot in response to dipolar forces in the patterned magnetic
structure. It is well described by an iterative solution of a continuous
variational procedure.",0602447v4
2006-02-22,Soliton pair dynamics in patterned ferromagnetic ellipses,"Confinement alters the energy landscape of nanoscale magnets, leading to the
appearance of unusual magnetic states, such as vortices, for example. Many
basic questions concerning dynamical and interaction effects remain unanswered,
and nanomagnets are convenient model systems for studying these fundamental
physical phenomena. A single vortex in restricted geometry, also known as a
non-localized soliton, possesses a characteristic translational excitation mode
that corresponds to spiral-like motion of the vortex core around its
equilibrium position. Here, we investigate, by a microwave reflection
technique, the dynamics of magnetic soliton pairs confined in lithographically
defined, ferromagnetic Permalloy ellipses. Through a comparison with
micromagnetic simulations, the observed strong resonances in the subgigahertz
frequency range can be assigned to the translational modes of vortex pairs with
parallel or antiparallel core polarizations. Vortex polarizations play a
negligible role in the static interaction between two vortices, but their
effect dominates the dynamics.",0602509v1
2006-06-09,Magnetic resonance studies of the fundamental spin-wave modes in individual submicron Cu/NiFe/Cu perpendicularly magnetized disks,"Spin wave spectra of perpendicularly magnetized disks with trilayers
consisting of a 100 nm permalloy (Py) layer sandwiched by two Cu layers of 30
nm, are measured individually with a Magnetic Resonance Force Microscope
(MRFM). It is demonstrated by 3D micromagnetic simulations that in disks having
sub-micron size diameters, the lowest energy spin wave mode of the saturated
state is not spatially uniform but rather is localized at the center of the
Py/Cu interface in the region of a minimum demagnetizing field.",0606245v3
2006-07-14,Exchange biasing and electric polarization with YMnO3,"We report on the growth and functional characterization of epitaxial thin
films of the multiferroic YMnO3. We show that using Pt as a seed layer on
SrTiO3(111) substrates, epitaxial YMnO3 films (0001) textured are obtained. An
atomic force microscope has been used to polarize electric domains revealing
the ferroelectric nature of the film. When a Permalloy layer is grown on top of
the YMnO3(0001) film, clear indications of exchange bias and enhanced
coercivity are observed at low temperature. The observation of coexisting
antiferromagnetism and electrical polarization suggests that the biferroic
character of YMnO3 can be exploited in novel devices.",0607378v1
2006-07-24,Magnetoresistance in Thin Permalloy Film (10nm-thick and 30-200nm-wide) Nanocontacts Fabricated by e-Beam Lithography,"In this paper we show spin dependent transport experiments in
nanoconstrictions ranging from 30 to 200nm. These nanoconstrictions were
fabricated combining electron beam lithography and thin film deposition
techniques. Two types of geometries have been fabricated and investigated. We
compare the experimental results with the theoretical estimation of the
electrical resistance. Finally we show that the magnetoresistance for the
different geometries does not scale with the resistance of the structure and
obtain drops in voltage of 20mV at 20Oe.",0607608v1
2006-08-24,Observation of standard spin-switch effects in F/S/F trilayers with a strong ferromagnet,"We have measured the superconducting transition temperature T_c of F/S/F
trilayers using Permalloy (Py=Ni_84 Fe_16) as a strongly polarized
ferromagnetic material. For a parallel (P) or anti-parallel (AP) alignment of
the magnetization directions of the outer ferromagnets, we observe a T_c
difference as large as 20 mK, with a stronger suppression of superconductivity
in the P state than in the AP state. This behavior is opposite to the recent
observations of Rusanov et al., Phys. Rev. B 73, 060505 (2006) in Py/Nb/Py
trilayers, but is consistent with earlier results on trilayers with Ni or CuNi
alloy as the ferromagnetic material.",0608545v1
2006-11-27,Nanomagnetic toggle switching of vortex cores on the picosecond time scale,"We present an ultrafast route for a controlled, toggle switching of magnetic
vortex cores with ultrashort unipolar magnetic field pulses. The switching
process is found to be largely insensitive to extrinsic parameters, like sample
size and shape, and it is faster than any field-driven magnetization reversal
process previously known from micromagnetic theory. Micromagnetic simulations
demonstrate that the vortex core reversal is mediated by a rapid sequence of
vortex-antivortex pair-creation and annihilation sub-processes. Specific
combinations of field pulse strength and duration are required to obtain a
controlled vortex cores reversal. The operational range of this reversal
mechanism is summarized in a switching diagram for a 200 nm Permalloy disk.",0611668v2
2006-12-15,Domain Nucleation and Annihilation in Uniformly Magnetized State under Current Pulses in Narrow Ferromagnetic Wires,"We investigate the current-driven magnetization dynamics in narrow Permalloy
wires by means of Lorentz microscopy and electron holography. Current pulses
are found to transform the magnetic structure in the uniformly magnetized state
below the Curie temperature. A variety of magnetic states including reversed
magnetic domains are randomly obtained in low probability. The dynamics of
vortices found in most of observed magnetic states seems to play a key role in
triggering the magnetization reversal.",0612383v2
2007-02-05,Demagnetization Protocols for Frustrated Interacting Nanomagnet Arrays,"We report a study of demagnetization protocols for frustrated arrays of
interacting single domain permalloy nanomagnets by rotating the arrays in a
changing magnetic field. The most effective demagnetization is achieved by not
only stepping the field strength down while the sample is rotating, but by
combining each field step with an alternation in the field direction. By
contrast, linearly decreasing the field strength or stepping the field down
without alternating the field direction leaves the arrays with a larger
remanent magnetic moment. These results suggest that non-monotonic variations
in field magnitude around and below the coercive field are important for the
demagnetization process.",0702084v1
2007-03-21,Ultrafast Vortex-Core Reversal Dynamics in Ferromagnetic Nanodots,"To verify the exact underlying mechanism of ultrafast vortex-core reversal as
well as the vortex state stability we conducted numerical calculations of the
dynamic evolution of magnetic vortices in Permalloy cylindrical nanodots under
an oscillating in-plane magnetic field over a wide range of the frequency and
amplitude. The calculated results reveal different kinds of the non-trivial
dynamic responses of vortices to the driving external field. In particular, the
results offer insight into the 10 ps scale underlying physics of the ulrafast
vortex-core reversals driven by small amplitude (~10 Oe) in-plane fields. This
work also provides fundamentals of how to manipulate effectively the dynamical
switching of the vortex-core orientation.",0703538v1
2007-03-22,Spin-Torque Ferromagnetic Resonance Measurements of Damping in Nanomagnets,"We measure the magnetic damping parameter a in thin film CoFeB and permalloy
(Py) nanomagnets at room temperature using ferromagnetic resonance driven by
microwave frequency spin-transfer torque. We obtain $\alpha_{CoFeB} = 0.014 \pm
0.003$ and $\alpha_{Py}=0.010 \pm 0.002$, values comparable to measurements for
extended thin films, but significantly less than the effective damping
determined previously for similar nanomagnets by fits to time-domain studies of
large-angle magnetic excitations and magnetic reversal. The greater damping
found for the large amplitude nanomagnet dynamics is attributed to the
nonlinear excitation of non-uniform magnetic modes.",0703577v1
2007-06-12,Graphene Spin Transistor,"Graphitic nanostructures, e.g. carbon nanotubes (CNT) and graphene, have been
proposed as ideal materials for spin conduction[1-7]; they have long electronic
mean free paths[8] and small spin-orbit coupling[9], hence are expected to have
very long spin-scattering times. In addition, spin injection and detection in
graphene opens new opportunities to study exotic electronic states such as the
quantum Hall[10,11] and quantum spin Hall[9] states, and spin-polarized edge
states[12] in graphene ribbons. Here we perform the first non-local four-probe
experiments[13] on graphene contacted by ferromagnetic Permalloy electrodes. We
observe sharp switching and often sign-reversal of the non-local resistance at
the coercive field of the electrodes, indicating definitively the presence of a
spin current between injector and detector. The non-local resistance changes
magnitude and sign quasi-periodically with back-gate voltage, and
Fabry-Perot-like oscillations[6,14,15] are observed, consistent with
quantum-coherent transport. The non-local resistance signal can be observed up
to at least T = 300 K.",0706.1597v1
2007-10-10,Microwave photovoltage and photoresistance effects in ferromagnetic microstrips,"We investigate the dc electric response induced by ferromagnetic resonance in
ferromagnetic Permalloy (Ni80Fe20) microstrips. The resulting magnetization
precession alters the angle of the magnetization with respect to both dc and rf
current. Consequently the time averaged anisotropic magnetoresistance (AMR)
changes (photoresistance). At the same time the time-dependent AMR oscillation
rectifies a part of the rf current and induces a dc voltage (photovoltage). A
phenomenological approach to magnetoresistance is used to describe the distinct
characteristics of the photoresistance and photovoltage with a consistent
formalism, which is found in excellent agreement with experiments performed on
in-plane magnetized ferromagnetic microstrips. Application of the microwave
photovoltage effect for rf magnetic field sensing is discussed.",0710.1974v3
2007-11-30,Domain wall pinning and potential landscapes created by constrictions and protrusions in ferromagnetic nanowires,"The potential experienced by transverse domain walls (TDWs) in the vicinity
of asymmetric constrictions or protrusions in thin Permalloy nanowires is
probed using spatially resolved magneto-optical Kerr effect measurements. Both
types of traps are found to act as pinning centers for DWs. The strength of
pinning is found to depend on the trap type as well as on the chirality of the
incoming DW; both types of traps are seen to act either as potential wells or
potential barriers, also depending on the chirality of the DW. Micromagnetic
simulations have been performed that are in good qualitative agreement with the
experimental results.",0711.5026v3
2008-01-30,Time-Resolved X-ray Microscopy of Spin-Torque-Induced Magnetic Vortex Gyration,"Time-resolved X-ray microscopy is used to image the influence of alternating
high-density currents on the magnetization dynamics of ferromagnetic vortices.
Spin-torque induced vortex gyration is observed in micrometer-sized permalloy
squares. The phases of the gyration in structures with different chirality are
compared to an analytical model and micromagnetic simulations, considering both
alternating spinpolarized currents and the current's Oersted field. In our case
the driving force due to spin-transfer torque is about 70% of the total
excitation while the remainder originates from the current's Oersted field.
This finding has implications to magnetic storage devices using spin-torque
driven magnetization switching and domain-wall motion.",0801.4719v1
2008-02-01,Ultrafast dynamics of a magnetic antivortex - Micromagnetic simulations,"The antivortex is a fundamental magnetization structure which is the
topological counterpart of the well-known magnetic vortex. We study here the
ultrafast dynamic behavior of an isolated antivortex in a patterned Permalloy
thin-film element. Using micromagnetic simulations we predict that the
antivortex response to an ultrashort external field pulse is characterized by
the production of a new antivortex as well as of a temporary vortex, followed
by an annihilation process. These processes are complementary to the recently
reported response of a vortex and, like for the vortex, lead to the reversal of
the orientation of the antivortex core region. In addition to its fundamental
interest, this dynamic magnetization process could be used for the generation
and propagation of spin waves for novel logical circuits.",0802.0093v1
2008-04-07,"Energy equilibriation processes of electrons, magnons and phonons on the femtosecond timescale","By means of time-resolved Kerr spectroscopy experiments we relate the energy
dissipation processes on the femtosecond (electron-spin relaxation time
$\tau_{el-sp}$) and nanosecond timescale (Gilbert relaxation $\tau_{\alpha}$)
and compare the results to the first microscopic model, which was proposed by
Koopmans. For both energy dissipation processes, Elliot-Yafet scattering is
proposed as the dominant contributor. We controllably manipulate the energy
dissipation processes by transition metal doping (Pd) and rare earth doping
(Dy) of a Permalloy film and find that while a change of $\tau_{\alpha}$ of
more than a factor two is observed, \tau_{el-sp}$ remains constant, contrary to
the predictions of the model. We explain the discrepancies by relaxation
channels not considered in the original microscopic model and identify thereby
the applicability of the model and possible necessary extensions to the model.",0804.0985v1
2008-05-19,Magnetic dipole induced guided vortex motion,"We present evidence of magnetically controlled guided vortex motion in a
hybrid superconductor/ferromagnet nanosystem consisting of an Al film on top of
a square array of permalloy square rings. When the rings are magnetized with an
in-plane external field H, an array of point-like dipoles with moments
antiparallel to H, is formed. The resulting magnetic template generates a
strongly anisotropic pinning potential landscape for vortices in the
superconducting layer. Transport measurements show that this anisotropy is able
to confine the flux motion along the high symmetry axes of the square lattice
of dipoles. This guided vortex motion can be either re-routed by 90 degrees by
simply changing the dipole orientation or even strongly suppressed by inducing
a flux-closure magnetic state with very low stray fields in the rings.",0805.2857v1
2008-07-11,Universal criterion and phase diagram for switching a magnetic vortex core in soft magnetic nanodots,"The universal criterion for ultrafast vortex-core switching between the up-
and down-core bistates in soft magnetic nanodots was investigated by
micromagnetic simulations along with analytical calculations. Vortex-core
switching occurs whenever the velocity of vortex-core motion reaches the
critical velocity that is expressed as (e.g. m/s for Permalloy), where Aex is
the exchange stiffness, and is the gyromagnetic ratio. On the basis of the
above results, phase diagrams for the vortex-core switching event and switching
times with respect to both the amplitude and frequency of applied circularly
rotating magnetic field were calculated, which offer practical guidance for
implementing nanodots in vortex states into future solid-state
information-storage devices.",0807.1848v5
2008-10-20,High domain wall velocity at zero magnetic field induced by low current densities in spin-valve nanostripes,"Current-induced magnetic domain wall motion at zero magnetic field is
observed in the permalloy layer of a spin-valve-based nanostripe using
photoemission electron microscopy. The domain wall movement is hampered by
pinning sites, but in between them high domain wall velocities (exceeding 150
m/s) are obtained for current densities well below $10^{12} \unit{A/m^2}$,
suggesting that these trilayer systems are promising for applications in domain
wall devices in case of well controlled pinning positions. Vertical spin
currents in these structures provide a potential explanation for the increase
in domain wall velocity at low current densities.",0810.3576v2
2008-12-29,Vortex dynamics in confined stratified conditions,"We report on linear spin dynamics in the vortex state of the Permalloy dots
subjected to stratified (magnetic) field. We demonstrate experimentally and by
simulations the existence of two distinct dynamic regimes corresponding to the
vortex stable and metastable states. Breaking cylindrical symmetry leads to
unexpected eigenmodes frequency splitting in the stable state and appearance of
new eigenmodes in the metastable state above the vortex nucleation field.
Dynamic response in the metastable state strongly depends on relative
orientation of the external rf pumping and the bias magnetic fields. These
findings may be relevant for different vortex states in confined and stratified
conditions.",0812.4954v1
2009-03-01,Depinning of domain walls with an internal degree of freedom,"Taking into account the coupling between the position of the wall and an
internal degree of freedom, namely its phase $\phi$, we examine, in the rigid
wall approximation, the dynamics of a magnetic domain wall subject to a weak
pinning potential. We determine the corresponding force-velocity
characteristics, which display several unusual features when compared to
standard depinning laws. At zero temperature, there exists a bistable regime
for low forces, with a logarithmic behavior close to the transition. For weak
pinning, there occurs a succession of bistable transitions corresponding to
different topological modes of the phase evolution. At finite temperature, the
force-velocity characteristics become non-monotonous. We compare our results to
recent experiments on permalloy nanowires.",0903.0175v1
2009-03-12,Observation of localized ferromagnetic resonance in a continuous ferromagnetic film via magnetic resonance force microscopy,"We present Magnetic Resonance Force Microscopy (MRFM) measurements of
Ferromagnetic Resonance (FMR) in a 50 nm thick permalloy film, tilted with
respect to the direction of the external magnetic field. At small probe-sample
distances the MRFM spectrum breaks up into multiple modes, which we identify as
local ferromagnetic resonances confined by the magnetic field of the MRFM tip.
Micromagnetic simulations support this identification of the modes and show
they are stabilized in the region where the dipolar tip field has a component
anti-parallel to the applied field.",0903.2285v1
2009-05-28,Resonant Nonlinear Damping of Quantized Spin Waves in Ferromagnetic Nanowires,"We use spin torque ferromagnetic resonance to measure the spectral properties
of dipole-exchange spin waves in permalloy nanowires. Our measurements reveal
that geometric confinement has a profound effect on the damping of spin waves
in the nanowire geometry. The damping parameter of the lowest-energy quantized
spin wave mode depends on applied magnetic field in a resonant way and exhibits
a maximum at a field that increases with decreasing nanowire width. This
enhancement of damping originates from a nonlinear resonant three-magnon
confluence process allowed at a particular bias field value determined by
quantization of the spin wave spectrum in the nanowire geometry.",0905.4699v2
2009-05-29,Ferromagnetic resonance linewidth in ultrathin films with perpendicular magnetic anisotropy,"Transition metal ferromagnetic films with perpendicular magnetic anisotropy
(PMA) have ferromagnetic resonance (FMR) linewidths that are one order of
magnitude larger than soft magnetic materials, such as pure iron (Fe) and
permalloy (NiFe) thin films. A broadband FMR setup has been used to investigate
the origin of the enhanced linewidth in Ni$|$Co multilayer films with PMA. The
FMR linewidth depends linearly on frequency for perpendicular applied fields
and increases significantly when the magnetization is rotated into the film
plane. Irradiation of the film with Helium ions decreases the PMA and the
distribution of PMA parameters. This leads to a great reduction of the FMR
linewidth for in-plane magnetization. These results suggest that fluctuations
in PMA lead to a large two magnon scattering contribution to the linewidth for
in-plane magnetization and establish that the Gilbert damping is enhanced in
such materials ($\alpha \approx 0.04$, compared to $\alpha \approx 0.002$ for
pure Fe).",0905.4779v2
2009-06-01,Modeling of microwave-assisted switching in micron-sized magnetic ellipsoids,"The microwave assisted magnetisation reversal is modelled in a permalloy
micron-sized magnetic ellipsoid. Our simulations confirm that this process
requires less field than magnetisation reversal under a static field. This is
due to a different reversal mode which in case of the microwave-assisted
process is always a ripple structure. During the magnetisation reversal two
stages: nucleation and relaxation are distinguished. The nucleation process is
governed by spinwave instabilities. The relaxation process is related to the
domain expansion through domain wall propagation determined by the precessional
motion of magnetic moments in the center of the domain walls. As a consequence,
the switching time is a complex oscillating function of the microwave
frequency.",0906.0263v1
2009-09-30,Phase diagram of magnetic configurations for soft magnetic nanodots of circular and elliptical shape obtained by micromagnetic simulation,"Magnetic disks or dots of soft magnetic material of sub-micron dimensions may
have as the lowest energy magnetic configuration a single-domain structure,
with magnetization either perpendicular of parallel to the plane, or else may
form magnetic vortices. The properties of these vortices may be used to encode
data bits, in magnetic memory applications. In the present work the OOMMF code
was used to compute by micromagnetic simulation the energy and the
magnetization of circular and elliptical nanodots of permalloy. For the
elliptical magnetic dots the analysis was made for variable thickness and
length of major axis, keeping a 2:1 axis ratio. From the simulations, a phase
diagram was constructed, where the ground state configurations of the nanodots
are represented in a diagram of nanodot height versus length of the major axis
$2a$ of the ellipse. The phase diagram obtained includes regions with one and
two vortices; it is similar, but more complex than that derived using a
numerical scaling approach, since it includes configurations with lateral
vortices. These diagrams are useful as guides for the choice of dimensions of
elliptical nanodots for practical applications.",0909.5686v1
2009-10-16,Transverse instabilities of multiple vortex chains in superconductor-ferromagnet bilayers,"Using scanning tunneling microscopy and Ginzburg-Landau simulations we
explore vortex configurations in magnetically coupled NbSe$_2$-Permalloy
superconductor-ferromagnet bilayer. The Permalloy film with stripe domain
structure induces periodic local magnetic induction in the superconductor
creating a series of pinning-antipinning channels for externally added magnetic
flux quanta. Such laterally confined Abrikosov vortices form quasi-1D arrays
(chains). The transitions between multichain states occur through propagation
of kinks at the intermediate fields. At high fields we show that the system
becomes non-linear due to a change in both the number of vortices and the
confining potential. The longitudinal instabilities of the resulting vortex
structures lead to vortices `levitating' in the anti-pinning channels.",0910.3030v1
2009-11-10,Spin-wave propagation in a microstructured magnonic crystal,"Transmission of microwave spin waves through a microstructured magnonic
crystal in the form of a permalloy waveguide of a periodically varying width
was studied experimentally and theoretically. The spin wave characteristics
were measured by spatially-resolved Brillouin light scattering microscopy. A
rejection frequency band was clearly observed. The band gap frequency was
controlled by the applied magnetic field. The measured spin-wave intensity as a
function of frequency and propagation distance is in good agreement with a
model calculation.",0911.1920v1
2009-11-11,Temperature dependent nucleation and annihilation of individual magnetic vortices,"We studied the temperature dependence of the magnetization reversal in
individual submicron permalloy disks with micro-Hall and bend-resistance
magnetometry. The nucleation field exhibits a nonmonotonic dependence with
positive and negative slopes at low and high temperatures, respectively, while
the annihilation field monotonically decreases with increasing temperature, but
with distinctly different slopes at low and high temperatures. Our analysis
suggests that at low temperatures vortex nucleation and annihilation proceeds
via thermal activation over an energy barrier, while at high temperatures they
are governed by a temperature dependence of the saturation magnetization.",0911.2267v1
2010-01-20,Precise probing spin wave mode frequencies in the vortex state of circular magnetic dots,"We report on detailed broadband ferromagnetic resonance measurements of
azimuthal and radial spin wave excitations in circular Permalloy dots in the
vortex ground state. Dots with aspect ratio (Beta =height over radius) varied
from 0.03 to 0.1 were explored. We found that for Beta exceeding approximately
0.05, variation of the spin wave eigenfrequencies with Beta deviates from the
predicted dependence. The frequency splitting of two lowest azimuthal modes was
observed. The experimentally observed dependence of the frequency splitting on
beta was reasonably well described by dynamic splitting model accounting the
spin-waves and, vortex gyrotropic mode interaction.",1001.3605v1
2010-05-07,Non-adiabatic spin torque investigated using thermally activated magnetic domain wall dynamics,"Using transmission electron microscopy, we investigate the thermally
activated motion of domain walls (DWs) between two positions in permalloy
(Ni80Fe20) nanowires at room temperature. We show that this purely thermal
motion is well described by an Arrhenius law, allowing for a description of the
DW as a quasi-particle in a 1D potential landscape. By injecting small
currents, the potential is modified, allowing for the determination of the
non-adiabatic spin torque: the non-adiabatic coefficient is 0.010 +/- 0.004 for
a transverse DW and 0.073 +/- 0.026 for a vortex DW. The larger value is
attributed to the higher magnetization gradients present.",1005.1168v1
2010-06-02,Magnetization pinning in conducting films demonstrated using broadband ferromagnetic resonance,"The broadband microstrip ferromagnetic resonance technique has been applied
for detection and characterization of a magnetic inhomogeneity in a film
sample. In the case of a 100nm thick Permalloy film an additional magnetically
depleted top sub-layer, practically unidentifiable by the conventional
ferromagnetic resonance setup, has been detected and characterized. These
results have been confirmed by Brillouin light scattering spectroscopy
revealing the fact that the optical properties of the additional sub-layer do
not differ much from those of the bulk of the film. Subsequent characterization
of a large number of other presumably single-layer films with thicknesses in
the range 30-100nm using the same ferromagnetic resonance technique also
revealed the same effect.",1006.0331v1
2010-10-08,"A unified first-principles study of Gilbert damping, spin-flip diffusion and resistivity in transition metal alloys","Using a formulation of first-principles scattering theory that includes
disorder and spin-orbit coupling on an equal footing, we calculate the
resistivity $\rho$, spin flip diffusion length $l_{sf}$ and the Gilbert damping
parameter $\alpha$ for Ni$_{1-x}$Fe$_x$ substitutional alloys as a function of
$x$. For the technologically important Ni$_{80}$Fe$_{20}$ alloy, permalloy, we
calculate values of $\rho = 3.5 \pm 0.15$ $\mu$Ohm-cm, $l_{sf}=5.5 \pm 0.3$ nm,
and $\alpha= 0.0046 \pm 0.0001$ compared to experimental low-temperature values
in the range $4.2-4.8$ $\mu$Ohm-cm for $\rho$, $5.0-6.0$ nm for $l_{sf}$, and
$0.004-0.013$ for $\alpha$ indicating that the theoretical formalism captures
the most important contributions to these parameters.",1010.1626v3
2011-02-01,One-dimentional magnonic crystal as a medium with magnetically tunable disorder on a periodical lattice,"We show that periodic magnetic nanostructures (magnonic crystals) represent
an ideal system for studying excitations on disordered periodical lattices
because of the possibility of controlled variation of the degree of disorder by
varying the applied magnetic field. Ferromagnetic resonance (FMR) data
collected inside minor hysteresis loops for a periodic array of Permalloy
nanowires of alternating width and magnetic force microscopy images of the
array taken after running each of these loops were used to establish convincing
evidence that there is a strong correlation between the type of FMR response
and the degree of disorder of the magnetic ground state. We found two types of
dynamic responses: anti-ferromagnetic (AFM) and ferromagnetic (FM), which
represent collective spin wave modes or collective magnonic states. Depending
on the history of sample magnetization either AFM or FM state is either the
fundamental FMR mode or represents a state of a magnetic defect on the
artificial crystal. A fundamental state can be transformed into a defect one
and vice versa by controlled magnetization of the sample.",1102.0069v1
2011-02-09,Enhancement of the response of non-uniform resonance modes of a nanostructure in the Picoprobe microwave-current injection ferromagnetic resonance,"The non-uniform standing spin-wave modes in thin magnetic films and
nanostructures provide important information about surfaces and buried
interfaces. Very often they are lacking in the recorded ferromagnetic resonance
spectra for symmetry reasons. In this work we experimentally demonstrate that
by direct injection of microwave currents into an array of Permalloy
nanostripes using a microscopic microwave coaxial to coplanar adaptor one can
efficiently excite non-uniform standing spin wave modes with odd symmetry. The
proposed method is quick and allows easy spatial mapping of magnetic properties
with the resolution down to 100 microns. We have validated this method using an
example from a periodical array of nanostripes. The results from direct current
injection are compared to that of microstrip-based FMR measurements.",1102.1805v2
2011-02-22,Ab-initio calculation of the Gilbert damping parameter via linear response formalism,"A Kubo-Greenwood-like equation for the Gilbert damping parameter $\alpha$ is
presented that is based on the linear response formalism. Its implementation
using the fully relativistic Korringa-Kohn-Rostoker (KKR) band structure method
in combination with Coherent Potential Approximation (CPA) alloy theory allows
it to be applied to a wide range of situations. This is demonstrated with
results obtained for the bcc alloy system Fe$_x$Co$_{1-x}$ as well as for a
series of alloys of permalloy with 5d transition metals.
  To account for the thermal displacements of atoms as a scattering mechanism,
an alloy-analogy model is introduced. The corresponding calculations for Ni
correctly describe the rapid change of $\alpha$ when small amounts of
substitutional Cu are introduced.",1102.4551v1
2011-04-19,Spin relaxation mechanism in Silver nanowires covered with MgO protection layer,"Spin-flip mechanism in Ag nanowires with MgO surface protection layers has
been investigated by means of nonlocal spin valve measurements using
Permalloy/Ag lateral spin valves. The spin flip events mediated by surface
scattering are effectively suppressed by the MgO capping layer. The spin
relaxation process was found to be well described in the framework of
Elliott-Yafet mechanism and then the probabilities of spin-filp scattering for
phonon or impurity mediated momentum scattering is precisely determined in the
nanowires. The temperature dependent spin-lattice relaxation follows the
Bloch-Gr\""uneisen theory and falls on to a universal curve for the monovalent
metals as in the Monod and Beuneu scaling determined from the conduction
electron spin resonance data for bulk.",1104.3718v2
2011-05-27,Mechanisms of nonlinear spin-wave emission from a microwave driven nanocontact,"We present a micromagnetic study of linear and nonlinear spin-wave modes
excited in an extended permalloy thin film by a microwave driven nanocontact.
We show that the linear mode having the frequency equal to the excitation
frequency (f) is driven by the ac Oersted field component perpendicular to the
static external field (applied in-plane of the sample). The nonlinear mode with
the frequency f /2 is excited as an independent eigenmode within a parametric
longitudinal pumping process (due ac Oersted field component parallel to the
bias field). Spectral positions of those modes are determined both in the space
and phase domain. The results are important for the transfer of information
coded into spin-waves between nanocontacts, and for synchronization of spin
transfer torque nano-oscillators.",1105.5512v1
2011-06-21,All-Optical Excitation and Detection of Picosecond Dynamics of Ordered Arrays of Nanomagnets with Varying Areal Density,"We have demonstrated optical excitation and detection of collective
precessional dynamics in arrays of coupled Ni80Fe20 (permalloy) nanoelements
with systematically varying areal density by an all-optical time-resolved Kerr
microscope. We have applied this technique to precisely determine three
different collective regimes in these arrays. At very high areal density, a
single uniform collective mode is observed where the edge modes of the
constituent elements are suppressed. At intermediate areal densities, three
nonuniform collective modes appear and at very low areal density, we observe
noncollective dynamics and only the centre and edge modes of the constituent
elements appear.",1106.4113v2
2011-10-04,Observation of non-linear magnetic vortex gyration by X-ray microscopy and micromagnetic simulations,"Magnetic vortex gyration in a 500 nm wide, 50 nm thick Permalloy square
platelet was investigated using time-resolved scanning transmission x-ray
microscopy and micromagnetic simulations. The response of the vortex core on an
in-plane oscillating magnetic field was studied as a function of the excitation
frequency and amplitude. Non-linear behavior was observed in the form of a
redshift of the gyrotropic resonance. I.e., when the excitation amplitude was
increased, the resonance frequency was found to decrease. The nonlinearity is
in agreement with extensive micromagnetic simulations. This work complements
previous reports on thinner nanostructures where a frequency blueshift was
observed.",1110.0828v1
2011-10-12,First-principles study of the spin-mixing conductance in Pt/Ni$_{81}$Fe$_{19}$ junctions,"Based on the spin-pumping theory and first-principles calculations, the
spin-mixing conductance (SMC) is theoretically studied for Pt/Permalloy
(Ni$_{81}$Fe$_{19}$, Py) junctions. We evaluate the SMC for ideally clean Pt/Py
junctions and examine the effects of interface randomness. We find that the SMC
is generally enhanced in the presence of interface roughness as compared to the
ideally clean junctions. Our estimated SMC is in good quantitative agreement
with the recent experiment for Pt/Py junctions. We propose possible routes to
increase the SMC in Pt/Py junctions by depositing a foreign magnetic metal
layer in Pt, offering guidelines for designing the future spintronic devices.",1110.2546v1
2011-11-18,Exchange Bias Induced by the Fe3O4 Verwey transition,"We present a study of the exchange bias in different configurations of V2O3
thin films with ferromagnetic layers. The exchange bias is accompanied by a
large vertical shift in the magnetization. These effects are only observed when
V2O3 is grown on top of Ni80Fe20 permalloy. The magnitude of the vertical shift
is as large as 60% of the total magnetization which has never been reported in
any system. X-Ray diffraction studies show that the growth conditions promote
the formation of a ferrimagnetic Fe3O4 interlayer. The change in the easy
magnetization axis of Fe3O4 across the Verwey transition at 120 K is correlated
with the appearance of exchange bias and vertical shift in magnetization. Both
phenomena disappear above 120 K, indicating for the first time a direct
relationship between the magnetic signature of the Verwey transition and
exchange bias.",1111.4255v2
2011-11-20,Detection of picosecond magnetization dynamics of 50 nm magnetic dots down to the single dot regime,"We report an all-optical time-domain detection of picosecond magnetization
dynamics of arrays of 50 nm Ni80Fe20 (permalloy) dots down to the single
nanodot regime. In the single nanodot regime the dynamics reveals one dominant
resonant mode corresponding to the edge mode of the 50 nm dot with slightly
higher damping than that of the unpatterned thin film. With the increase in
areal density of the array both the precession frequency and damping increases
significantly due to the increase in magnetostatic interactions between the
nanodots and a mode splitting and sudden jump in apparent damping are observed
at an edge-to-edge separation of 50 nm.",1111.4625v1
2012-01-02,Localized domain-wall excitations in patterned magnetic dots probed by broadband ferromagnetic resonance,"We investigate the magnetization dynamics in circular Permalloy dots with
spatially separated magnetic vortices interconnected by domain walls (double
vortex state). We identify a novel type of quasi one-dimensional (1D) localised
spin wave modes confined along domain walls, connecting each of two vortex
cores with two edge half-antivortices. Variation of the mode eigenfrequencies
with the dot size is in quantitative agreement with the developed model, which
considers a dipolar origin of the localized 1D spin waves or so-called
Winter\'s magnons [J.M. Winter, Phys.Rev. 124, 452 (1961)]. These spin waves
are analogous to the displacement waves of strings, and could be excited in a
wide class of patterned magnetic nanostructures possessing domain walls, namely
in triangular, square, circular or elliptic magnetic dots.",1201.0482v1
2012-02-03,Domain - wall - induced magnetoresistance in pseudo spin-valve/superconductor hybrid structures,"We have studied the interaction between magnetism and superconductivity in a
pseudo-spin-valve structure consisting of a Co/Cu/Py/Nb layer sequence. We are
able to control the magnetization reversal process and monitor it by means of
the giant magnetoresistance effect during transport measurements. By placing
the superconducting Nb-film on the top of the permalloy (Py) electrode instead
of putting it in between the two ferromagnets, we minimize the influence of
spin scattering or spin accumulation onto the transport properties of Nb.
Magnetotransport data reveal clear evidence that the stray fields of domain
walls (DWs) in the pseudo-spin-valve influence the emerging superconductivity
close to the transition temperature by the occurrence of peak-like features in
the magneto-resistance characteristic. Direct comparison with magnetometry data
shows that the resistance peaks occur exactly at the magnetization reversal
fields of the Co and Py layers, where DWs are generated. For temperatures near
the superconducting transition the amplitude of the DW-induced
magnetoresistance increases with decreasing temperature, reaching values far
beyond the size of the giant magnetoresistive response of our structure in the
normal state.",1202.0715v1
2012-02-20,Stability of Spinmotive Force in Perpendicularly Magnetized Nanowires under High Magnetic Fields,"Spinmotive force induced by domain wall motion in perpendicularly magnetized
nanowires is numerically demonstrated. We show that using nanowires with large
magnetic anisotropy can lead to a high stability of spinmotive force under
strong magnetic fields. We observe spinmotive force in the order of tens of
microvolt in a multilayered Co/Ni nanowire and in the order of several hundred
microvolt in a FePt nanowire; the latter is two orders of magnitude greater
than that in permalloy nanowires reported previously. The narrow structure and
low mobility of a domain wall under magnetic fields in perpendicularly
magnetized nanowires permits downsizing of spinmotive force devices.",1202.4256v2
2012-02-25,Magnetization states and switching in narrow-gapped ferromagnetic nanorings,"We study permalloy nanorings that are lithographically fabricated with narrow
gaps that break the rotational symmetry of the ring while retaining the vortex
ground state, using both micromagnetic simulations and magnetic force
microscopy (MFM). The vortex chirality in these structures can be readily set
with an in-plane magnetic field and easily probed by MFM due to the field
associated with the gap, suggesting such rings for possible applications in
storage technologies. We find that the gapped ring edge characteristics (i.e.,
edge profile and gap shape) are critical in determining the magnetization
switching field, thus elucidating an essential parameter in the controls of
devices that might incorporate such structures.",1202.5596v1
2012-03-01,Phase diagram of magnetic domain walls in spin valve nano-stripes,"We investigate numerically the transverse versus vortex phase diagram of
head-to-head domain walls in Co/Cu/Py spin valve nano-stripes (Py: Permalloy),
in which the Co layer is mostly single domain while the Py layer hosts the
domain wall. The range of stability of the transverse wall is shifted towards
larger thickness compared to single Py layers, due to a magnetostatic screening
effect between the two layers. An approached analytical scaling law is derived,
which reproduces faithfully the phase diagram.",1203.0192v2
2012-03-22,A Numerical Model of Crossed Andreev Reflection and Charge Imbalance,"We present a numerical model of local and nonlocal transport properties in a
lateral spin valve structure consisting of two magnetic electrodes in contact
with a third perpendicular superconducting electrode. By considering the
transport paths for a single electron incident at the local F/S interface - in
terms of probabilities of crossed or local Andreev reflection, elastic
cotunneling or quasiparticle transport - we show that this leads to nonlocal
charge imbalance. We compare this model with experimental data from an
aluminum-permalloy (Al/Py) lateral spin valve geometry device and demonstrate
the effectiveness of this simple approach in replicating experimental behavior.",1203.4949v2
2012-03-28,Spin Hall Angle Quantification from Spin Pumping and Microwave Photoresistance,"We present a method to quantify the spin Hall angle (SHA) with spin pumping
and microwave photoresistance measurements. With this method, we separate the
inverse spin Hall effect (ISHE) from other unwanted effects for permalloy/Pt
bilayers using out-of-plane microwave excitation. Through microwave
photoresistance measurements, the in- and out-of-plane precessing angles of the
magnetization are determined and enabled for the exact determination of the
injected pure spin current. This method is demonstrated with an almost perfect
Lorentz line-shape for the obtained ISHE signal and the frequency independent
SHA value as predicted by theory. By varying the Pt thickness, the SHA and
spin-diffusion length of Pt is quantified as 0.012 (0.001) and 8.3 (0.9) nm,
respectively.",1203.6175v1
2012-07-26,Spin-orbit-coupling induced domain-wall resistance in diffusive ferromagnets,"We investigate diffusive transport through a number of domain wall (DW)
profiles of the important magnetic alloy Permalloy taking into account
simultaneously noncollinearity, alloy disorder, and spin-orbit coupling fully
quantum mechanically, from first principles. In addition to observing the known
effects of magnetization mistracking and anisotropic magnetoresistance, we
discover a not-previously identified contribution to the resistance of a DW
that comes from spin-orbit-coupling-mediated spin-flip scattering in a textured
diffusive ferromagnet. This adiabatic DW resistance, which should exist in all
diffusive DWs, can be observed by varying the DW width in a systematic fashion
in suitably designed nanowires.",1207.6277v2
2012-08-24,Domain-wall induced large magnetoresistance effects at zero applied field in ballistic nanocontacts,"We determine magnetoresistance effects in stable and clean permalloy
nanocontacts of variable cross-section, fabricated by UHV deposition and
in-situ electromigration. To ascertain the magnetoresistance (MR) effects
originating from a magnetic domain wall, we measure the resistance values with
and without such a wall at zero applied field. In the ballistic transport
regime, the MR ratio reaches up to 50% and exhibits a previously unobserved
sign change. Our results can be reproduced by recent atomistic calculations for
different atomic configurations of the nanocontact, highlighting the importance
of the detailed atomic arrangement for the MR effect.",1208.4985v1
2012-11-02,Dynamic Spin Injection into Chemical Vapor Deposited Graphene,"We demonstrate dynamic spin injection into chemical vapor deposition (CVD)
grown graphene by spin pumping from permalloy (Py) layers. Ferromagnetic
resonance measurements at room temperature reveal a strong enhancement of the
Gilbert damping at the Py/graphene interface, exceeding that observed in even
Py/platinum interfaces. Similar results are also shown on Co/graphene layers.
This enhancement in the Gilbert damping is understood as the consequence of
spin pumping at the interface driven by magnetization dynamics. Our
observations suggest a strong enhancement of spin-orbit coupling in CVD
graphene, in agreement with earlier spin valve measurements.",1211.0492v1
2012-11-07,Dipolar coupling between nanopillar spin valves and magnetic quantum cellular automata arrays,"We experimentally demonstrate magnetostatic coupling between a nanopillar
pseudo spin valve structure and a linear array of dipole coupled Permalloy
nanomagnets. Using magnetic force microscopy, we study the interaction between
the spin valve and the first element of the array, and present evidence that
the nanomagnet couples with the hard layer of the spin valve for two spin
valves with distinctly different composition. Our study includes a statistical
analysis of antiferromagnetic order within the linear array, and provides
insight into the range of behavior that these arrays can display. These results
bear directly on the design of magnetic quantum cellular automata (MQCA) logic
devices, showing that multilayer devices can couple to simple nanomagnets.
Redesigning the hard layer of the magnetoresistive devices would make them
operational as an electronic input that will allow integration of MQCA networks
in complex electronic circuitry.",1211.1536v2
2012-12-07,Brillouin Light Scattering Spectra as local Temperature Sensors for Thermal Magnons and Acoustic Phonons,"We demonstrate the use of the micro-Brillouin light scattering (micro-BLS)
technique as a local temperature sensor for magnons in a Permalloy thin film
and phonons in the glass substrate. A systematic shift in the frequencies of
two thermally excited perpendicular standing spin wave modes as the film is
uniformly heated allows us to achieve a temperature resolution better than 2.5
K. We demonstrate that the micro-BLS spectra can be used to measure the local
temperatures of phonons and magnons across a thermal gradient. Such local
temperature sensors are useful for investigating spin caloritronic and thermal
transport phenomena in general.",1212.1520v2
2012-12-12,Giant magnetoimpedance of composite wires with an insulation layer,"Composite wires with a three-layered structure exhibit a large giant
magneto-impedance (GMI) effect, which can be used in sensitive magnetic field
sensors. To further investigate the origin of the GMI effect, composite wires
consisting of a highly conductive copper core, a silicon dioxide layer and an
outer Permalloy shell were prepared by radio frequency (RF) magnetron
sputtering. The GMI ratio was measured at various driving current frequencies
and with different insulating layer thicknesses. A theoretical model by
coupling the Maxwell equations to the Landau-Lifschitz-Gilbert equation was
developed to investigate the composite wire impedance and its dependence on
external magnetic field, current frequency and insulating layer thickness.
Experimental results corroborate the theoretical model.",1212.2745v2
2013-01-10,"Comment on ""Physical Origin and Generic Control of Magnonic Band Gaps of Dipole-Exchange Spin Waves in Width-Modulated Nanostrip Waveguides"" [K.-S. Lee, D.-S. Han, and S.-K. Kim, PRL 102, 127202 (2009), arXiv:0811.0411]","In Ref. [PRL 102, 127202 (2009)] Lee et al. reported the existence of large
magnonic bandgaps in one-dimensional width-modulated Permalloy nanostripe
waveguides based on OOMMF simulations. However, as the symmetry of the magnetic
field pulse they applied to excite the spin waves (SWs) was not general, the
entire set of SW branches with A symmetry was omitted from the magnonic band
structures (see below). This omission has unfortunately led to misleading
conclusions of, for instance, the number, width and position of the bandgaps.
We present here the full band structure based on three different theoretical
approaches that gave consistent predictions, thus corroborating the methods
employed, namely, a microscopic approach, OOMMF simulations, and a method based
on the linearized Landau-Lifshitz equation. Further, we provide a physical
interpretation using group theory.",1301.2036v1
2013-05-28,Magnonic band gaps in waveguides with a periodic variation of the saturation magnetization,"We present a micromagnetic analysis of spin-wave propagation in a magnonic
crystal realized as a permalloy spin-wave waveguide with a spatial periodical
variation of its saturation magnetization. Frequency band gaps were clearly
observed in the spin-wave transmission spectra and their origin is traced back
to an overlap of individual band gaps of the fundamental and the higher order
spin-wave width modes. The control of the depth, width and the position in
frequency and space of the rejection band gaps by the width areas with a
reduced magnetization and by the modulation level, are discussed in this study.",1305.6619v1
2013-09-09,Quantitative stray field imaging of a magnetic vortex core,"Thin-film ferromagnetic disks present a vortex spin structure whose dynamics,
added to the small size (~10 nm) of their core, earned them intensive study.
Here we use a scanning nitrogen-vacancy (NV) center microscope to
quantitatively map the stray magnetic field above a 1 micron-diameter disk of
permalloy, unambiguously revealing the vortex core. Analysis of both
probe-to-sample distance and tip motion effects through stroboscopic
measurements, allows us to compare directly our quantitative images to
micromagnetic simulations of an ideal structure. Slight perturbations with
respect to the perfect vortex structure are clearly detected either due to an
applied in-plane magnetic field or imperfections of the magnetic structures.
This work demonstrates the potential of scanning NV microscopy to map tiny
stray field variations from nanostructures, providing a nanoscale,
non-perturbative detection of their magnetic texture.",1309.2171v2
2013-09-24,Influence of heat flow directions on Nernst effects in Py/Pt bilayers,"We investigated the voltages obtained in a thin Pt strip on a Permalloy film
which was subject to in-plane temperature gradients and magnetic fields. The
voltages detected by thin W-tips or bond wires showed a purely symmetric effect
with respect to the external magnetic field which can be fully explained by the
planar Nernst effect (PNE). To verify the influence of the contacts
measurements in vacuum and atmosphere were compared and gave similar results.
We explain that a slightly in-plane tilted temperature gradient only shifts the
field direction dependence but does not cancel out the observed effects.
Additionally, the anomalous Nernst effect (ANE) could be induced by using thick
Au-tips which generated a heat current perpendicular to the sample plane. The
effect can be manipulated by varying the temperature of the Au-tips. These
measurements are discussed concerning their relevance in transverse spin
Seebeck effect measurements.",1309.6237v2
2013-10-17,Electrical Detection of Direct and Alternating Spin Current Injected from a Ferromagnetic Insulator into a Ferromagnetic Metal,"We report room temperature electrical detection of spin injection from a
ferromagnetic insulator (YIG) into a ferromagnetic metal (Permalloy, Py).
Non-equilibrium spins with both static and precessional spin polarizations are
dynamically generated by the ferromagnetic resonance of YIG magnetization, and
electrically detected by Py as dc and ac spin currents, respectively. The dc
spin current is electrically detected via the inverse spin Hall effect of Py,
while the ac spin current is converted to a dc voltage via the spin
rectification effect of Py which is resonantly enhanced by dynamic exchange
interaction between the ac spin current and the Py magnetization. Our results
reveal a new path for developing insulator spintronics, which is distinct from
the prevalent but controversial approach of using Pt as the spin current
detector.",1310.4840v1
2013-10-23,Exchange-dominated Standing Spin Wave Excitations under microwave irradiation in Ni80Fe20 Thin Films,"We investigated the microwave-assisted DC voltages of ferromagnetic
resonances and exchangedominated standing spin wave excitations in two
different in-plane magnetized permalloy thin films via homodyne detection. The
line shapes of ferromagnetic resonance spectra and the dispersion curves of
ferromagnetic resonance and standing spin wave are in agreement of previous
studies, while further investigations of DC voltage spectra for these two
excitations reveal that 1. unlike ferromagnetic resonance signals, the
anti-symmetrical line shapes of standing spin wave excitations are not depend
on the electromagnetic relative phase of assisted microwave, and 2. linewidths
of their DC voltage spectra are distinct. The complicated spin dynamics of
standing spin wave is consequently discussed by applying
Landau-Lifshitz-Gilbert equation in term of exchange interaction.",1310.6108v1
2013-11-04,Non-reciprocal Oersted field contribution to the current-induced frequency shift of magnetostatic surface waves,"The influence of an electrical current on the propagation of magnetostatic
surface waves is investigated in a relatively thick (40 nm) permalloy film both
experimentally and theoretically. Contrary to previously studied thinner films
where the dominating effect is the current-induced spin-wave Doppler shift, the
magnetic field generated by the current (Oersted field) is found to induce a
strong non-reciprocal frequency shift which overcompensates the Doppler shift.
The measured current induced frequency shift is in agreement with the developed
theory. The theory relates the sign of of the frequency shift to the spin wave
modal profiles. The good agreement between the experiment and the theory
confirms a recent prediction of a counter-intuitive mode localization for
magnetostatic surface waves in the dipole-exchange regime.",1311.0676v1
2013-11-13,Thermally activated in-plane magnetization rotation induced by spin torque,"We study the role of thermal fluctuations on the spin dynamics of a thin
permalloy film with a focus on the behavior of spin torque and find that the
thermally assisted spin torque results in new aspects of the magnetization
dynamics. In particular, we uncover the formation of a finite, spin
torque-induced, in-plane magnetization component. The orientation of the
in-plane magnetization vector depends on the temperature and the spin-torque
coupling. We investigate and illustrate that the variation of the temperature
leads to a thermally-induced rotation of the in-plane magnetization.",1311.3120v1
2013-11-30,Fabrication and characterisation of nanospintronic devices,"We report an improved fabrication scheme for carbon based nanospintronic
devices and demonstrate the necessity for a careful data analysis to
investigate the fundamental physical mechanisms leading to magnetoresistance.
The processing with a low-density polymer and an optimised recipe allows us to
improve the electrical, magnetic and structural quality of ferromagnetic
Permalloy contacts on lateral carbon nanotube (CNT) quantum dot spin valve
devices, with comparable results for thermal and sputter deposition of the
material. We show that spintronic nanostructures require an extended data
analysis, since the magnetisation can affect all characteristic parameters of
the conductance features and lead to seemingly anomalous spin transport. In
addition, we report measurements on CNT quantum dot spin valves that seem not
to be compatible with the orthodox theories for spin transport in such
structures.",1312.0159v1
2013-12-05,Strong impact of the eddy-current shielding on ferromagnetic resonance response of sub-skin-depth-thick conducting magnetic multilayers,"Exchange-coupled nonmagnetic (NM) and ferromagnetic (FM) conducting
multilayers are crucial for microwave spintronic devices of the future. We
demonstrate, experimentally and theoretically, that in broadband measurements
of ferromagnetic resonance (FMR) 10-70 nm-thick permalloy (Py) layers are
shielded from the dynamic magnetic field of the microstrip line by eddy
currents circulating in the NM capping layers, which strongly diminishes the
amplitude of magnetisation precession in the FM material. Our findings have
direct implications for designing broadband FMR and measurements of spin
current injection through interfaces realised by placing a conducting
multilayer above a microwave microstrip line. We show that the eddy-current
shielding is very strong at high microwave frequencies (30 GHz) even when the
thickness of the NM capping layer is <5 nm, which is well below the microwave
skin depth for Au, Cu, Ta, Pd, Pt and other NM metals technologically important
for spintronics.",1312.1404v2
2013-12-17,Manipulating domain wall chirality by current pulses in Permalloy/Ir nanostrips,"Using magnetic force microscopy and micromagnetic simulations, we studied the
effect of Oersted magnetic fields on the chirality of transverse magnetic
domain walls in Fe$_{20}$Ni$_{80}$/Ir bilayer nanostrips. Applying nanosecond
current pulses with a current density of around $2\times10^{12}$ A/m$^2$, the
chirality of a transverse domain wall could be switched reversibly and
reproducibly. These current densities are similar to the ones used for
current-induced domain wall motion, indicating that the Oersted field may
stabilize the transverse wall chirality during current pulses and prevent
domain wall transformations.",1312.4918v1
2014-01-22,Current-induced magnetization dynamics at the edge of a two-dimensional electron system with strong spin-orbit coupling,"We experimentally investigate electron transport through the interface
between a permalloy ferromagnet and the edge of a two-dimensional electron
system with strong Rashba-type spin-orbit coupling. We observe strongly
non-linear transport around zero bias at millikelvin temperatures. The observed
nonlinearity is fully suppressed above some critical values of temperature,
magnetic field, and current through the interface. We interpret this behavior
as the result of spin accumulation at the interface and its current-induced
absorption as a magnetization torque.",1401.5719v2
2014-04-03,Enhanced DC Spin Pumping into a Fluctuating Ferromagnet near Tc,"A linear-response formulation of the dc spin pumping, i.e., a spin injection
from a precessing ferromagnet into an adjacent spin sink, is developed in view
of describing many-body effects caused by spin fluctuations in the spin sink.
It is shown that, when an itinerant ferromagnet near Tc is used as the spin
sink, the spin pumping is largely increased owing to the fluctuation
enhancement of the spin conductance across the precessing ferromagnet/spin sink
interface. As an example, the enhanced spin pumping from permalloy into nickel
palladium alloy (Tc ~ 20K) is analyzed by means of a self-consistent
renormalization scheme, and it is predicted that the enhancement can be as
large as tenfold.",1404.0768v2
2014-04-03,Anomalously Weak Cooper Pair-breaking by Exchange Energy in Ferromagnet/Superconductor Bilayers,"We report the superconducting transition temperature $T_c$ vs. thickness
$d_F$ of Ferromagnet/Superconductor (F/S) bilayers, where F is a strong $3d$
ferromagnet (Ni, Ni$_{0.81}$Fe$_{0.19}$ (Permalloy), Co$_{0.5}$Fe$_{0.5}$) and
S = Nb, taken from superfluid density measurements rather than resistivity. By
regrouping the many physical parameters that appear in theory, we show that the
effective exchange energy is determined from the F film thickness $d_F$ where
$T_c$ vs. $d_F$ begins to flatten out. Using this rearranged theory we
conclude: 1) the effective exchange energy, $E_{ex}$, is about 15 times smaller
than measured by ARPES and 5 times smaller than deduced in previous studies
similar to ours; 2) the dirty-limit coherence length, $\xi_{F}$, for Cooper
pairs in F is larger than the electron mean free path, $\ell_F$; and 3) the
$3d$-F/Nb interface is enough of a barrier that Cooper pairs typically must hit
it several times before getting through. The Py/Nb and CoFe/Nb interfaces are
more transparent than the Ni/Nb interface.",1404.1032v1
2014-04-04,Observation of inverse spin Hall effect in bismuth selenide,"Bismuth Selenide (Bi2Se3) is a topological insulator exhibiting helical spin
polarization and strong spin-orbit coupling. The spin-orbit coupling links the
charge current to spin current via the spin Hall effect (SHE). We demonstrate a
Bi2Se3 spin detector by injecting the pure spin current from a magnetic
permalloy layer to a Bi2Se3 thin film and detect the inverse SHE in Bi2Se3. The
spin Hall angle of Bi2Se3 is found to be 0.0093 and the spin diffusion length
in Bi2Se3 to be 6.2 nm at room temperature. Our results suggest that
topological insulators with strong spin-orbit coupling can be used in
functional spintronic devices.",1404.1146v2
2014-09-04,Detection of the dc inverse spin Hall effect due to spin pumping in a novel meander-stripline geometry,"The dc voltage obtained from the inverse spin Hall effect (iSHE) due to spin
pumping in ferromagnet/normal-metal (NM) bilayers can be unintentionally
superimposed with magnetoresistive rectification of ac charge currents in the
ferromagnetic layer. We introduce a geometry in which these spurious
rectification voltages vanish while the iSHE voltage is maximized. In this
geometry, a quantitative study of the dc iSHE is performed in a broad frequency
range for Permalloy/NM multilayers with NM={Pt, Ta, Cu/Au, Cu/Pt}. The
experimentally recorded voltages can be fully ascribed to the iSHE due to spin
pumping. Furthermore we measure a small iSHE voltage in single CoFe thin films.",1409.1290v1
2014-09-30,Origin of inverse Rashba-Edelstein effect at Cu/Bi interface using lateral spin valves,"The spin transport and spin-to-charge current conversion properties of
bismuth are investigated using permalloy/copper/bismuth (Py/Cu/Bi)lateral spin
valve structures. The spin current is strongly absorbed at the surface of Bi,
leading to ultra-short spin diffusion lengths. A spin-to-charge current
conversion is measured, which is attributed to the inverse Rashba-Edelstein
effect at the Cu/Bi interface. The spin-current-induced charge current is found
to change direction with increasing temperature. A theoretical analysis relates
this behavior to the complex spin structure and dispersion of the surface
states at the Fermi energy. The understanding of this phenomenon opens novel
possibilities to exploit spin-orbit coupling to create, manipulate, and detect
spin currents in 2D systems.",1409.8540v2
2014-10-24,Rectification of radio frequency current in giant magnetoresistance spin valve,"We report on a highly efficient spin diode effect in an exchange-biased
spin-valve giant magnetoresistance (GMR) strips. In such multilayer structures,
symmetry of the current distribution along the vertical direction is broken
and, as a result, a non-compensated Oersted field acting on the magnetic free
layer appears. This field, in turn, is a driving force of magnetization
precessions. Due to the GMR effect, resistance of the strip oscillates
following the magnetization dynamics. This leads to rectification of the
applied radio frequency current and induces a direct current voltage $V_{DC}$.
We present a theoretical description of this phenomenon and calculate the spin
diode signal, $V_{DC}$, as a function of frequency, external magnetic field,
and angle at which the external field is applied. A satisfactory quantitative
agreement between theoretical predictions and experimental data has been
achieved. Finally, we show that the spin diode signal in GMR devices is
significantly stronger than in the anisotropic magnetoresistance
permalloy-based devices.",1410.6672v1
2015-01-12,Direct Imaging of Complex Spin Ice Behavior and Ordered Sublattices in Artificial Ferromagnetic Quasicrystals,"We have imaged magnetization textures of permalloy films patterned into
Penrose P2 tilings (P2T) using scanning electron microscopy with polarization
analysis (SEMPA). P2T film segments have near-uniform, bipolar magnetization,
similar to artificial spin ices, but with asymmetric vertex coordination that
induces a more complex spin ice behavior mediated by exchange interactions in
vertex domain walls. Numerical simulations including long-range dipole
interactions agree with SEMPA images of as-grown P2T, and predict a
ferromagnetic ground state for a 2D P2T lattice of classical Ising spins.",1501.02760v1
2015-02-22,Spin-valve Effect in NiFe/MoS2/NiFe Junctions,"Two-dimensional (2D) layered transition metal dichalcogenides (TMDs) have
been recently proposed as appealing candidate materials for spintronic
applications owing to their distinctive atomic crystal structure and exotic
physical properties arising from the large bonding anisotropy. Here we
introduce the first MoS2-based spin-valves that employ monolayer MoS2 as the
nonmagnetic spacer. In contrast with what expected from the semiconducting
band-structure of MoS2, the vertically sandwiched-MoS2 layers exhibit metallic
behavior. This originates from their strong hybridization with the Ni and Fe
atoms of the Permalloy (Py) electrode. The spin-valve effect is observed up to
240 K, with the highest magnetoresistance (MR) up to 0.73% at low temperatures.
The experimental work is accompanied by the first principle electron transport
calculations, which reveal an MR of ~ 9% for an ideal Py/MoS2/Py junction. Our
results clearly identify TMDs as a promising spacer compound in magnetic tunnel
junctions and may open a new avenue for the TMDs-based spintronic applications.",1502.06154v2
2015-03-30,Suppression of Spin Pumping Between Ni$_{80}$Fe$_{20}$ and Cu by a Graphene Interlayer,"We compare ferromagnetic resonance measurements of Permalloy
Ni$_{80}$Fe$_{20}$ (Py) films sputtered onto Cu(111) films with and without a
graphene (Gr) interlayer grown by chemical vapor deposition before Py
deposition. A two-angle sputtering method ensured that neither Gr nor Py was
degraded by the sample preparation process. We find the expected damping
enhancement from spin pumping for the Py/Cu case and no detectable enhancement
for the Py/Gr/Cu case. Since damping is sensitive to effects other than spin
pumping, we used magnetometry to verify that differences in Py magnetostatic
properties are not responsible for the difference in damping. We attribute the
suppression of spin pumping in Py/Gr/Cu to the large contact resistance of the
Gr/Cu interface.",1503.08777v1
2015-04-01,Multiscale modeling of ultrafast element-specific magnetization dynamics of ferromagnetic alloys,"A hierarchical multiscale approach to model the magnetization dynamics of
ferromagnetic ran- dom alloys is presented. First-principles calculations of
the Heisenberg exchange integrals are linked to atomistic spin models based
upon the stochastic Landau-Lifshitz-Gilbert (LLG) equation to calculate
temperature-dependent parameters (e.g., effective exchange interactions,
damping param- eters). These parameters are subsequently used in the
Landau-Lifshitz-Bloch (LLB) model for multi-sublattice magnets to calculate
numerically and analytically the ultrafast demagnetization times. The developed
multiscale method is applied here to FeNi (permalloy) as well as to copper-
doped FeNi alloys. We find that after an ultrafast heat pulse the Ni sublattice
demagnetizes faster than the Fe sublattice for the here-studied FeNi-based
alloys.",1504.00199v1
2015-05-18,Evidence on the macroscopic length scale spin coherence for the edge currents in a narrow HgTe quantum well,"We experimentally investigate spin-polarized electron transport between two
ferromagnetic contacts, placed at the edge of a two-dimensional electron system
with band inversion. The system is realized in a narrow (8~nm) HgTe quantum
well, the ferromagnetic side contacts are formed from a pre-magnetized
permalloy film. In zero magnetic field, we find a significant edge current
contribution to the transport between two ferromagnetic contacts. We
experimentally demonstrate that this transport is sensitive to the mutual
orientation of the magnetization directions of two 200~$\mu$m-spaced
ferromagnetic leads. This is a direct experimental evidence on the
spin-coherent edge transport over the macroscopic distances. Thus, the spin is
extremely robust at the edge of a two-dimensional electron system with band
inversion, confirming the helical spin-resolved nature of edge currents.",1505.04535v1
2015-08-03,Static magnetic proximity effect in Pt/Ni$_{1-x}$Fe$_x$ bilayers investigated by x-ray resonant magnetic reflectivity,"We present x-ray resonant magnetic reflectivity (XRMR) as a very sensitive
tool to detect proximity induced interface spin polarization in Pt/Fe,
Pt/Ni$_{33}$Fe$_{67}$, Pt/Ni$_{81}$Fe$_{19}$ (permalloy), and Pt/Ni bilayers.
We demonstrate that a detailed analysis of the reflected x-ray intensity gives
insight in the spatial distribution of the spin polarization of a non-magnetic
metal across the interface to a ferromagnetic layer. The evaluation of the
experimental results with simulations based on optical data from ab initio
calculations provides the induced magnetic moment per Pt atom in the spin
polarized volume adjacent to the ferromagnet. We find the largest spin
polarization in Pt/Fe and a much smaller magnetic proximity effect in Pt/Ni.
Additional XRMR experiments with varying photon energy are in good agreement
with the theoretical predictions for the energy dependence of the magnetooptic
parameters and allow identifying the optical dispersion $\delta$ and absorption
$\beta$ across the Pt L3-absorption edge.",1508.00379v1
2015-08-06,Interface-driven spin-torque ferromagnetic resonance by Rashba coupling at the interface between non-magnetic materials,"The Rashba-Edelstein effect stems from the interaction between the electron's
spin and its momentum induced by spin-orbit interaction at an interface or a
surface. It was shown that the inverse Rashba-Edelstein effect can be used to
convert a spin- into a charge current. Here, we demonstrate that a Bi/Ag Rashba
interface can even drive an adjacent ferromagnet to resonance. We employ a
spin-torque ferromagnetic resonance excitation/detection scheme which was
developed originally for a bulk spin-orbital effect, the spin Hall effect. In
our experiment, the direct Rashba-Edelstein effect generates an oscillating
spin current from an alternating charge current driving the magnetization
precession in a neighboring permalloy (Py, Ni80Fe20) layer. Electrical
detection of the magnetization dynamics is achieved by a rectification
mechanism of the time dependent multilayer resistance arising from the
anisotropic magnetoresistance.",1508.01410v1
2015-09-03,All-Optical Vector Measurement of Spin-Orbit-Induced Torques Using Both Polar and Quadratic Magneto-Optic Kerr Effects,"We demonstrate that the magneto-optic-Kerr effect with normal light incidence
can be used to obtain quantitative optical measurements of both components of
spin-orbit-induced torque (both the antidamping and effective-field components)
in heavy-metal/ferromagnet bilayers. This is achieved by analyzing the
quadratic Kerr effect as well as the polar Kerr effect. The two effects can be
distinguished by properly selecting the polarization of the incident light. We
use this all-optical technique to determine the spin-orbit torques generated by
a series of Pt/Permalloy samples, finding values in excellent agreement with
spin-torque ferromagnetic resonance measurements.",1509.01266v1
2015-09-10,Role of hexagonal boron nitride in protecting ferromagnetic nanostructures from oxidation,"Ferromagnetic contacts are widely used to inject spin polarized currents into
non-magnetic materials such as semiconductors or 2-dimensional materials like
graphene. In these systems, oxidation of the ferromagnetic materials poses an
intrinsic limitation on device performance. Here we investigate the role of
ex-situ transferred chemical vapour deposited hexagonal boron nitride (hBN) as
an oxidation barrier for nanostructured cobalt and permalloy electrodes. The
chemical state of the ferromagnets was investigated using X-ray photoemission
electron microscopy owing to its high sensitivity and lateral resolution. We
have compared the oxide thickness formed on ferromagnetic nanostructures
covered by hBN to uncovered reference structures. Our results show that hBN
reduces the oxidation rate of ferromagnetic nanostructures suggesting that it
could be used as an ultra-thin protection layer in future spintronic devices.",1509.03087v2
2015-12-15,Moderate Positive Spin Hall Angle in Uranium,"We report measurements of spin pumping and the inverse spin Hall effect in
Ni80Fe20/Uranium bilayers designed to study the efficiency of spin-charge
interconversion in a super-heavy element. We employ broad-band ferromagnetic
resonance on extended films to inject a spin current from the Ni80Fe20
(permalloy) into the uranium layer, which is then converted into an electric
field by the inverse spin Hall effect. Surprisingly, our results suggest a spin
mixing conductance of order 2x10 e19 m-2 and a positive spin Hall angle of
0.004, which are both merely comparable to those of several transition metals.
These results thus support the idea that the electronic configuration may be at
least as important as the atomic number in governing spin pumping across
interfaces and subsequent spin Hall effects. In fact, given that both the
magnitude and the sign are unexpected based on trends in d-electron systems,
materials with unfilled f-electron orbitals may hold additional exploration
avenues for spin physics.",1512.04903v1
2016-01-21,Vortex Dynamics-Mediated Low-Field Magnetization Switching in an Exchange-Coupled System,"A magnetic vortex has attracted significant attention since it is a
topologically stable magnetic structure in a soft magnetic nanodisk. Many
studies have been devoted to understanding the nature of magnetic vortex in
isolated systems. Here we show a new aspect of a magnetic vortex the dynamics
of which strongly affects the magnetic structures of environment. We exploit a
nanodot of an exchange-coupled bilayer with a soft magnetic Ni81Fe19
(permalloy; Py) having a magnetic vortex and a perpendicularly magnetized
L10-FePt exhibiting a large switching field (Hsw). The vortex dynamics with
azimuthal spin waves makes the excess energy accumulate in the Py, which
triggers the reversed-domain nucleation in the L10-FePt at a low magnetic
field. Our results shed light on the non-local mechanism of a reversed-domain
nucleation, and provide with a route for efficient Hsw reduction that is needed
for ultralow-power spintronic devices.",1601.05521v1
2016-01-27,Quantification of a propagating spin-wave-packet created by an ultrashort laser pulse in a thin film of magnetic metal,"Coherent spin-wave generation by focused ultrashort laser pulse irradiation
was investigated for a permalloy thin film at micrometer scale using an
all-optical space and time-resolved magneto-optical Kerr effect. The spin-wave
packet propagating perpendicular to magnetization direction was clearly
observed, however that propagating parallel to the magnetization direction was
not observed. The propagation length, group velocity, center frequency, and
packet-width of the observed spin-wave packet were evaluated and quantitatively
explained in terms of the propagation of a magneto-static spin-wave driven by
ultrafast change of an out-of-plane demagnetization field induced by the
focused-pulse laser.",1601.07247v1
2016-01-28,Spin-Cherenkov effect in a magnetic nanostrip with interfacial Dzyaloshinskii-Moriya interaction,"Spin-Cherenkov effect enables strong excitations of spin waves (SWs) with
nonlinear wave dispersions. The Dzyaloshinskii-Moriya interaction (DMI) results
in anisotropy and nonreciprocity of SWs propagation. In this work, we study the
effect of the interfacial DMI on SW Cherenkov excitations in permalloy
thin-film strips within the framework of micromagnetism. By performing
micromagnetic simulations, it is shown that coherent SWs are excited when the
velocity of a moving magnetic source exceeds the propagation velocity of the
SWs. Moreover, the threshold velocity of the moving magnetic source with finite
DMI can be reduced compared to the case of zero DMI. It thereby provides a
promising route towards efficient SW generation and propagation, with potential
applications in spintronic and magnonic devices.",1601.07755v2
2016-02-11,Thermal spin injection and interface insensitivity in permalloy/aluminum metallic non-local spin valves,"We present measurements of thermal and electrical spin injection in nanoscale
metallic non-local spin valve (NLSV) structures. Informed by measurements of
the Seebeck coefficient and thermal conductivity of representative films made
using a micromachined Si-N thermal isolation platform, we use simple analytical
and finite element thermal models to determine limits on the thermal gradient
driving thermal spin injection and calculate the spin dependent Seebeck
coefficient to be $-0.5\ \mu\mathrm{V}/\mathrm{K}< S_{s}<-1.3\
\mu\mathrm{V}/\mathrm{K}$. This is comparable in terms of the fraction of the
absolute Seebeck coefficient to previous results, despite dramatically smaller
electrical spin injection signals. Since the small electrical spin signals are
likely caused by interfacial effects, we conclude that thermal spin injection
is less sensitive to the FM/NM interface, and possibly benefits from a layer of
oxidized ferromagnet, which further stimulates interest in thermal spin
injection for applications in sensors and pure spin current sources.",1602.03859v2
2016-04-02,Influence of Joule heating on current-induced domain wall depinning,"The domain wall depinning from a notch in a Permalloy nanostrip on top of a
${\rm SiO_2/Si}$ substrate is studied theoretically under application of static
magnetic fields and the injection of short current pulses. The influence of
Joule heating on current-induced domain wall depinning is explored
self-consistently by coupling the magnetization dynamics in the ferromagnetic
strip to the heat transport throughout the system. Our results indicate that
Joule heating plays a remarkable role in these processes, resulting in a
reduction in the critical depinning field and/or in a temporary destruction of
the ferromagnetic order for typically injected current pulses. In agreement
with experimental observations, similar pinning-depinning phase diagrams can be
deduced for both current polarities when the Joule heating is taken into
account. These observations, which are incompatible with the sole contribution
of spin transfer torques, provide a deeper understanding of the physics
underlying these processes and establish the real scope of the spin transfer
torque. They are also relevant for technological applications based on
current-induced domain-wall motion along soft strips.",1604.00522v2
2016-04-15,Chaotic dynamics of magnetic domain walls in nanowires,"The nonlinear dynamics of a transverse domain wall (TDW) in Permalloy and
Nickel nanostrips with two artificially patterned pinning centers is studied
numerically up to rf frequencies. The phase diagram frequency - driving
amplitude shows a rich variety of dynamical behaviors depending on the material
parameters and the type and shape of pinning centers. We find that T-shaped
traps (antinotches) create a classical double well Duffing potential that leads
to a small chaotic region in the case of Nickel and a large one for Py. In
contrast, the rectangular constrictions (notches) create an exponential
potential that leads to larger chaotic regions interspersed with periodic
windows for both Py and Ni. The influence of temperature manifests itself by
enlarging the chaotic region and activating thermal jumps between the pinning
sites while reducing the depinning field at low frequency in the notched
strips.",1604.04438v1
2016-04-16,A broadband Ferromagnetic Resonance dipper probe for magnetic damping measurements from 4.2 K to 300 K,"A dipper probe for broadband Ferromagnetic Resonance (FMR) operating from 4.2
K to room temperature is described. The apparatus is based on a 2-port
transmitted microwave signal measurement with a grounded coplanar waveguide.
The waveguide generates a microwave field and records the sample response. A
3-stage dipper design is adopted for fast and stable temperature control. The
temperature variation due to FMR is in the milli-Kelvin range at liquid helium
temperature. We also designed a novel FMR probe head with a spring-loaded
sample holder. Improved signal-to-noise ratio and stability compared to a
common FMR head are achieved. Using a superconducting vector magnet we
demonstrate Gilbert damping measurements on two thin film samples using a
vector network analyzer with frequency up to 26 GHz: 1) A Permalloy film of 5
nm thickness and 2) a CoFeB film of 1.5 nm thickness. Experiments were
performed with the applied magnetic field parallel and perpendicular to the
film plane.",1604.04688v1
2016-04-22,Nanoscale control of heat and spin conductance in artificial spin chains,"We describe a mechanism to control energy and magnetisation currents in an
artificial spin-chain, consisting of an array of Permalloy nano-disks coupled
through the magneto-dipolar interaction. The chain is kept out of equilibrium
by two thermal baths with different temperatures connected to its ends, which
control the current propagation. Transport is enhanced by applying a uniform
radio frequency pump field resonating with some of the spin-wave modes of the
chain. Moreover, the two currents can be controlled independently by tuning the
static field applied on the chain. Thus we describe two effective means for the
independent control of coupled currents and the enhancement of thermal and
spin-wave conductivity in a realistic magnonics device, suggesting that similar
effects could be observed in a large class of nonlinear oscillating systems.",1604.06572v3
2016-05-10,Nanocavity optomechanical torque magnetometry and radiofrequency susceptometry,"Nanophotonic optomechanical devices allow observation of nanoscale vibrations
with sensitivity that has dramatically advanced metrology of nanomechanical
structures [1-9] and has the potential to impact studies of nanoscale physical
systems in a similar manner [10, 11]. Here we demonstrate this potential with a
nanophotonic optomechanical torque magnetometer and radiofrequency (RF)
magnetic susceptometer. Exquisite readout sensitivity provided by a nanocavity
integrated within a torsional nanomechanical resonator enables observations of
the unique net magnetization and RF-driven responses of single mesoscopic
magnetic structures in ambient conditions. The magnetic moment resolution is
sufficient for observation of Barkhausen steps in the magnetic hysteresis of a
lithographically patterned permalloy island [12]. In addition, significantly
enhanced RF susceptibility is found over narrow field ranges and attributed to
thermally assisted driven hopping of a magnetic vortex core between neighboring
pinning sites [13]. The on-chip magneto-susceptometer scheme offers a promising
path to powerful integrated cavity optomechanical devices for quantitative
characterization of magnetic micro- and nanosystems in science and technology.",1605.03138v2
2016-06-03,Crystal Structure Manipulation of the Exchange Bias in an Antiferromagnetic Film,"Exchange bias is one of the most extensively studied phenomena in magnetism,
since it exerts a unidirectional anisotropy to a ferromagnet (FM) when coupled
to an antiferromagnet (AFM) and the control of the exchange bias is therefore
very important for technological applications, such as magnetic random access
memory and giant magnetoresistance sensors. In this letter, we report the
crystal structure manipulation of the exchange bias in epitaxial hcp Cr2O3
films. By epitaxially growing twined (10-10) oriented Cr2O3 thin films, of
which the c axis and spins of the Cr atoms lie in the film plane, we
demonstrate that the exchange bias between Cr2O3 and an adjacent permalloy
layer is tuned to in-plane from out-of-plane that has been observed in (0001)
oriented Cr2O3 films. This is owing to the collinear exchange coupling between
the spins of the Cr atoms and the adjacent FM layer. Such a highly anisotropic
exchange bias phenomenon is not possible in polycrystalline films.",1606.01086v1
2016-06-09,Snell's Law for Spin Waves,"We report the experimental observation of Snell's law for magneto-static spin
waves in thin ferromagnetic Permalloy films by imaging incident, refracted and
reflected waves. We use a thickness step as the interface between two media
with different dispersion relation. Since the dispersion relation for
magneto-static waves in thin ferromagnetic films is anisotropic, deviations
from the isotropic Snell's law known in optics are observed for incidence
angles larger than 25\textdegree{} with respect to the interface normal between
the two magnetic media. Furthermore, we can show that the thickness step
modifies the wavelength and the amplitude of the incident waves. Our findings
open up a new way of spin wave steering for magnonic applications.",1606.02895v1
2016-09-20,Positive Exchange Bias between Permalloy and Twined (10-10)-Cr2O3 Films,"We report the discovery of a positive exchange bias between Ni80Fe20 (Py) and
twined (10-10)-Cr2O3 film near its blocking temperature (TB) when it is cooled
in an in-plane magnetic field applied along 45 degrees from the two spin
configurations of the Cr atoms. This is an abnormal behavior compared to the
negative exchange bias at all temperatures below TB when the cooling and
measuring magnetic fields are applied along one of the two spin configurations
of the Cr atoms. We speculate these results could be related to the exchange
interactions between the twined structure of the (10-10)-Cr2O3 film epitaxially
grown on the rutile (001)-TiO2 substrate.",1609.06216v1
2016-10-14,Electric-field tunable spin waves in PMN-PT/NiFe heterostructure: experiment and micromagnetic simulations,"We present a comprehensive theoretical and experimental study of
voltage-controlled standing spin waves resonance (SSWR) in PMN-PT/NiFe
multiferroic heterostructures patterned into microstrips. A spin-diode
technique was used to observe ferromagnetic resonance (FMR) mode and SSWR in
NiFe strip mechanically coupled with a piezoelectric substrate. Application of
an electric field to a PMNPT creates a strain in permalloy and thus shifts the
FMR and SSWR fields due to the magnetostriction effect. The experimental
results are compared with micromagnetic simulations and a good agreement
between them is found for dynamics of FMR and SSWR with and without electric
field. Moreover, micromagnetic simulations enable us to discuss the amplitude
and phase spatial distributions of FMR and SSWR modes, which are not directly
observable by means of spin diode detection technique.",1610.04500v1
2017-07-25,3D MOKE spin-orbit torque magnetometer,"We demonstrate simultaneous detection of current driven antidamping-like and
field-like spin-orbit torques in heavy metal/ferromagnetic metal bilayers by
measuring all three magnetization components m_(x,) m_y, and m_z using the
vector magneto-optic Kerr effect. We have also implemented a self-calibration
method to accurately determine the effective fields of spin-orbit torques. With
this technique, we investigate the magnitude and direction of spin-orbit
torques in a series of platinum/permalloy samples. The values found are in
excellent agreement with results obtained via quadratic magneto-optic Kerr
effect, planar Hall effect, and spin transfer ferromagnetic resonance
measurements.",1707.08565v1
2017-11-23,Effect of Notch Structure on Magnetic Domain Movement in Planar Nanowires,"We present the direct observation of magnetic domain motion in permalloy
nanowires with notches using a wide-field Kerr microscopy technique. The domain
wall motion can be modulated by the size and shape of the notch structure in
the nanowires. It is demonstrated that the coercive fields can be tuned by
modulating the notches. The experimental results are consistent with the
micro-magnetic simulation results. The relationship between the notch angle and
the domain nuclease are also studied. This work is useful for the design and
development of the notch-based spintronic devices.",1711.08788v1
2017-11-28,Transmission x-ray microscopy at low temperatures - analyzing supercurrents with high spatial resolution,"Scanning transmission x-ray microscopy has been used to image electric
currents in superconducting films at temperatures down to 20 K. The magnetic
stray field of supercurrents in a thin YBaCuO film is mapped into a
soft-magnetic coating of permalloy. The so created local magnetization of the
ferromagnetic film can be detected by dichroic absorption of polarized x-rays.
To enable high-quality measurements in transmission geometry the whole
heterostructure of ferromagnet, superconductor and single-crystalline substrate
has been thinned to an overall thickness of less than 1 micron. With this novel
technique local supercurrents can be analyzed in a wide range of temperatures
and magnetic fields. A magnetic resolution of less than 100nm together with
simultaneously obtained nanostructural data allow the correlation of local
supercurrents with the micro- and nanostructure of the superconducting film.",1711.10230v1
2018-05-21,"11,11,12,12-tetracyanonaphtho-2,6-quinodimethane in Contact with Ferromagnetic Electrodes for Organic Spintronics","Spinterface engineering has shown quite important roles in organic
spintronics as it can improve spin injection or extraction. In this study,
11,11,12,12-tetracyanonaptho-2,6-quinodimethane (TNAP) is introduced as an
interfacial layer for a prototype interface of Fe/TNAP. We report an
element-specific investigation of the electronic and magnetic structures of
Fe/TNAP system by use of near edge X-Ray absorption fine structure (NEXAFS) and
X-ray magnetic circular dichroism (XMCD). Strong hybridization between TNAP and
Fe and induced magnetization of N atoms in TNAP molecule are observed. XMCD sum
rule analysis demonstrates that the adsorption of TNAP reduces the spin moment
of Fe by 12%. In addition, induced magnetization in N K-edge of TNAP has also
been found with other commonly used ferromagnets in organic spintronics, such
as La0.7Sr0.3MnO3 and permalloy, which makes TNAP a very promising molecule for
spinterface engineering in organic spintronics.",1805.07906v1
2018-05-25,"Calculating the transport properties of magnetic materials from first-principles including thermal and alloy disorder, non-collinearity and spin-orbit coupling","A density functional theory based two-terminal scattering formalism that
includes spin-orbit coupling and spin non-collinearity is described. An
implementation using tight-binding muffin-tin orbitals combined with extensive
use of sparse matrix techniques allows a wide variety of inhomogeneous
structures to be flexibly modelled with various types of disorder including
temperature induced lattice and spin disorder. The methodology is illustrated
with calculations of the temperature dependent resistivity and magnetization
damping for the important substitutional disordered magnetic alloy Permalloy
(Py), Ni$_{80}$Fe$_{20}$. Comparison of calculated results with recent
experimental measurements of the damping (including its temperature dependence)
indicates that the scattering approach captures the most important
contributions to this important property.",1805.10062v1
2018-06-12,Asymmetric motion of magnetically actuated artificial cilia,"Most microorganisms use hair-like cilia with asymmetric beating to perform
vital bio-physical processes. In this paper, we demonstrate a novel fabrication
method for creating magnetic artificial cilia capable of such biologically
inspired asymmetrical beating pattern essential for creating microfluidic
transport in low Reynolds number. The cilia are fabricated using a lithographic
process in conjunction with deposition of magnetic nickel-iron permalloy to
create flexible filaments that can be manipulated by varying an external
magnetic field. A rotating permanent magnet is used to actuate the cilia. We
examine the kinematics of a cilium and demonstrate that the cilium motion is
defined by an interplay among elastic, magnetic, and viscous forces.
Specifically, the forward stroke is induced by the rotation of the magnet which
bends the cilium, whereas the recovery stroke is defined by the straightening
of the deformed cilium, releasing the accumulated elastic potential energy.
This difference in dominating forces acting during the forward stroke and the
recovery stroke leads to an asymmetrical beating pattern of the cilium. Such
magnetic cilia can find applications in microfluidic pumping, mixing, and other
fluid handling processes.",1806.04320v1
2018-06-15,Design of a CubeSat Payload to Test a Magnetic Measurement System for Space-borne Gravitational Wave Detectors,"Space observatories for gravitational radiation such as LISA are equipped
with dedicated on-board instrumentation capable of measuring magnetic fields
with low-noise conditions at millihertz frequencies. The reason is that the
core scientific payload can only operate successfully if the magnetic
environment meets certain strict low-frequency requirements. With this purpose,
a simplified version of the proposed magnetic measurement system for LISA has
been developed for a six-unit CubeSat, which will make it possible to improve
the technology readiness level (TRL) of the instrument. The special feature of
the experiment is that the magnetic sensors integrated in the payload are
magnetically shielded to low-frequency fluctuations by using a small
cylindrical permalloy enclosure. This will allow the in-flight noise
characterization of the system under the CubeSat orbit environment. Therefore,
a CubeSat platform will offer the opportunity to measure the capability of the
instrument and will guide the progress towards the improved magnetic
measurement system for LISA. This article describes the principal
characteristics and implementation of the CubeSat payload.",1806.05913v1
2018-06-25,Wideband and on-chip excitation for dynamical spin injection into graphene,"Graphene is an ideal material for spin transport as very long spin relaxation
times and lengths can be achieved even at room temperature. However, electrical
spin injection is challenging due to the conductivity mismatch problem. Spin
pumping driven by ferromagnetic resonance is a neat way to circumvent this
problem as it produces a pure spin current in the absence of a charge current.
Here, we show spin pumping into single layer graphene in micron scale devices.
A broadband on-chip RF current line is used to bring micron scale permalloy
(Ni$_{80}$Fe$_{20}$) pads to ferromagnetic resonance with a magnetic field
tunable resonance condition. At resonance, a spin current is emitted into
graphene, which is detected by the inverse spin hall voltage in a close-by
platinum electrode. Clear spin current signals are detected down to a power of
a few milliwatts over a frequency range of 2 GHz to 8 GHz. This compact device
scheme paves the way for more complex device structures and allows the
investigation of novel materials.",1806.09356v1
2018-09-04,Increasing the performance of the superconducting spin valve using a Heusler alloy,"We have studied superconducting properties of the spin-valve thin layer
heterostructures CoO$_x$/F1/Cu/F2/Cu/Pb where the ferromagnetic F1 layer was
standardly made of Permalloy whereas for the F2 layer we have taken a specially
prepared film of the Heusler alloy Co$_2$Cr$_{1-x}$Fe$_x$Al with a small degree
of spin polarization of the conduction band. The heterostructures demonstrate a
significant superconducting spin-valve effect, i.e. a complete switching on and
off of the superconducting current flowing through the system by manipulating
the mutual orientations of the magnetization of the F1 and F2 layers. The
magnitude of the effect is doubled in comparison with the previously studied
analogous multilayers with the F2 layer made of the strong ferromagnet Fe.
Theoretical analysis shows that a drastic enhancement of the switching effect
is due to a smaller exchange field in the heterostructure coming from the
Heusler film as compared to Fe. This enables to approach almost ideal
theoretical magnitude of the switching in the Heusler-based multilayer with the
F2 layer thickness of $\sim 1$\,nm.",1809.00876v1
2018-09-17,On the speed of domain walls in thin nanotubes: the transition from the linear to the magnonic regime,"Numerical simulations of domain wall propagation in thin nanotubes when an
external magnetic field is applied along the nanotube axis have shown an
unexpected behavior described as a transition from a linear to a magnonic
regime. As the applied magnetic field increases, the initial regime of linear
growth of the speed with the field is followed by a sudden change in slope
accompanied by the emission of spin waves. In this work an analytical formula
for the speed of the domain wall that explains this behavior is derived by
means of an asymptotic study of the Landau Lifshitz Gilbert equation for thin
nanotubes. We show that the dynamics can be reduced to a one dimensional
hyperbolic reaction diffusion equation, namely, the damped double Sine Gordon
equation, which shows the transition to the magnonic regime as the domain wall
speed approaches the speed of spin waves. This equation has been previously
found to describe domain wall propagation in weak ferromagnets with the
mobility proportional to the Dzyaloshinskii-Moriya interaction constant, for
Permalloy nanotubes the mobility is proportional to the nanotube radius.",1809.06278v3
2018-11-13,Enhanced domain wall velocity near a ferromagnetic instability,"Assuming a Fermi liquid behavior for $s$-conduction electrons, we rewrite the
extended Landau-Lifshitz-Gilbert (LLG) equation renormalized by interactions
through the Landau parameters $F^{a}_{l}$ ($l=0,1,2 \cdots$) in an explicit
form to describe the dynamic of a domain wall (DW) due to spin transfer torque
phenomenon. The interaction between spins of the \textit{s}-conduction
electrons explains qualitatively the DW velocity experimental observations in
$\mathrm{Ni_{81}}\mathrm{Fe_{19}}$ (Permalloy) recalculated by us without
defects or impurity hypothesis. Close to Stoner ferromagnetic instability point
where $F^{a}_{0} \approx -0.99$, the DW velocity becomes high
($v^{*}_{DW}\approx 600$ $ms^{-1}$) and critical spin current density becomes
reduced ($j^{*}_{c}\approx1\times10^{12}$ $Am^{-2}$) when compared to that
calculated by nonadiabatic approach. At the critical point, the DW velocity
diverges while critical spin current density at the same point goes to zero.
Our theory also provides a prediction to looking for materials in which is
possible applies a smallest critical spin current density and observes higher
DW velocity.",1811.05380v4
2018-11-14,Relation between spin Hall effect and anomalous Hall effect in 3$d$ ferromagnetic metals,"We study the mechanisms of the spin Hall effect (SHE) and anomalous Hall
effect (AHE) in 3$d$ ferromagnetic metals (Fe, Co, permalloy
(Ni$_{81}$Fe$_{19}$; Py), and Ni) by varying their resistivities and
temperature. At low temperatures where the phonon scattering is negligible, the
skew scattering coefficients of the SHE and AHE in Py are related to its spin
polarization. However, this simple relation breaks down for Py at higher
temperatures as well as for the other ferromagnetic metals at any temperature.
We find that, in general, the relation between the SHE and AHE is more complex,
with the temperature dependence of the SHE being much stronger than that of
AHE.",1811.05589v2
2019-11-03,Nanowire magnetic force sensors fabricated by focused electron beam induced deposition,"We demonstrate the use of individual magnetic nanowires (NWs), grown by
focused electron beam induced deposition (FEBID), as scanning magnetic force
sensors. Measurements of their mechanical susceptibility, thermal motion, and
magnetic response show that the NWs posses high-quality flexural mechanical
modes and a strong remanent magnetization pointing along their long axis.
Together, these properties make the NWs excellent sensors of weak magnetic
field patterns, as confirmed by calibration measurements on a micron-sized
current-carrying wire and magnetic scanning probe images of a permalloy disk.
The flexibility of FEBID in terms of the composition, geometry, and growth
location of the resulting NWs, makes it ideal for fabricating scanning probes
specifically designed for imaging subtle patterns of magnetization or current
density.",1911.00912v1
2019-11-03,Magnetic damping modulation in $IrMn_{3}/Ni_{80}Fe_{20}$ via the magnetic spin Hall effect,"Non-collinear antiferromagnets can have additional spin Hall effects due to
the net chirality of their magnetic spin structure, which provides for more
complex spin-transport phenomena compared to ordinary non-magnetic materials.
Here we investigated how ferromagnetic resonance of permalloy
($Ni_{80}Fe_{20}$) is modulated by spin Hall effects in adjacent epitaxial
$IrMn_{3}$ films. We observe a large dc modulation of the ferromagnetic
resonance linewidth for currents applied along the [001] $IrMn_{3}$ direction.
This very strong angular dependence of spin-orbit torques from dc currents
through the bilayers can be explained by the magnetic spin Hall effect where
$IrMn_{3}$ provides novel pathways for modulating magnetization dynamics
electrically.",1911.00943v1
2017-05-16,"Note: Derivative divide, a method for the analysis of broadband ferromagnetic resonance in the frequency domain","Broadband ferromagnetic resonance (bbFMR) spectroscopy is an established
experimental tool to quantify magnetic properties. Due to frequency-dependent
transmission of the microwave setup, bbFMR measurements in the frequency domain
require a suitable background removal method. Here, we present a measurement
and data analysis protocol that allows to perform quantitative frequency-swept
bbFMR measurements without the need for a calibration of the microwave setup.
The method, its limitations and advantages are described in detail. Finally the
method is applied to evaluate FMR spectra of a permalloy thin film. The
extracted material parameters are in very good agreement with those obtained
using a conventional analysis in field-space.",1705.05694v2
2018-07-09,Spin wave dynamics in artificial anti spin-ice systems: experimental and theoretical investigations,"Reversed structures of artificial spin-ice systems, where elongated holes
with elliptical shape (antidots) are arranged into a square array with two
orthogonal sublattices, are referred to as anti-squared spin-ice. Using
Brillouin light scattering spectroscopy and plane wave method calculations, we
investigate the spin wave propagation perpendicular to the applied field
direction for two 20 nm thick Permalloy nanostructures which differ by the
presence of single and double elliptical antidots. For the spin waves
propagation along the principal antidot lattice axis, the spectrum consists of
flat bands separated by several frequency gaps which are the effect of spin
wave amplitude confinement in the regions between antidots. Contrarily, for
propagation direction at 45 degrees with respect to the antidot symmetry axis,
straight and narrow channels of propagation are formed, leading to broadening
of bands and closing of the magnonics gaps. Interestingly, in this case, extra
magnonic band gaps occur due to the additional periodicity along this
direction. The width and the position of these gaps depend on the presence of
single or double antidots. In this context, we discuss possibilities for the
tuning of spin wave spectra in anti-squared spin ice structures.",1807.03016v1
2018-07-27,Optimization of Multi-Frequency Magnonic Waveguides with Enhanced Group Velocities by Exchange Coupled Ferrimagnet/Ferromagnet Bilayers,"We report broadband spectroscopy and numerical analysis by which we explore
propagating spin waves in a magnetic bilayer consisting of a 23 nm thick
permalloy film deposited on 130 nm thick $Y_{3}Fe_{5}O_{12}$. In the bilayer,
we observe a characteristic mode that exhibits a considerably larger group
velocity at small in-plane magnetic field than both the magnetostatic and
perpendicular standing spin waves. Using the finite element method, we confirm
the observations by simulating the mode profiles and dispersion relations. They
illustrate the hybridization of spin wave modes due to exchange coupling at the
interface. The high-speed propagating mode found in the bilayer can be utilized
to configure multi-frequency spin wave channels enhancing the performance of
spin wave based logic devices.",1807.10508v2
2018-10-05,Remagnetization in the array of ferromagnetic nanowires with periodic and quasiperiodic order,"We investigate experimentally and theoretically the magnetization reversal
process in one-dimensional magnonic structures composed of permalloy nanowires
of the two different widths and finite length arranged in a periodic and
quasiperiodic order. The main features of the hysteresis loop are determined by
different shape anisotropies of the component elements and the dipolar
interactions between them. We showed, that the dipolar interactions between
nanowires forming a ribbon can be controlled by change a distance between the
neighboring ribbons. The quasiperiodic order can influence the hysteresis loop
by introduction additional tiny switching steps when the dipolar interactions
are sufficiently strong.",1810.02796v1
2018-10-09,Non-uniform spin wave softening in 2D magnonic crystals as a tool for opening omnidirectional magnonic band gaps,"By means of the plane wave method we study spin wave dynamics in
two-dimensional bi-component magnonic crystals based on a squeezed hexagonal
lattice and consist of a permalloy thin film with cobalt inclusions. We explore
the dependence of a spin wave frequency on the external magnetic field,
especially in weak fields where the mode softening takes place. For considered
structures, the mode softening proves to be highly non-uniform on both the mode
number and the wave vector. We found this effect to be responsible for the
omnidirectional band gap opening. Moreover, we show that the enhancement of the
demagnetizing field caused by the squeezing of the structure is of crucial
importance for the non-uniform mode softening. This allows us to employ this
mechanism to design magnonic gaps with different sensitivity for the tiny
change of the external field. The effects we have found should be useful in
designing and optimization of spin wave filters highly tunable by a small
external magnetic field.",1810.04005v3
2018-10-19,Magnon properties of random alloys,"We study magnon properties in terms of spin stiffness, Curie temperatures and
magnon spectrum of Fe-Ni, Co-Ni and Fe-Co random alloys using a combination of
electronic structure calculations and atomistic spin dynamics simulations.
Influence of the disorder are studied in detail by use of large supercells with
random atomic arrangement. It is found that disorder affects the magnon
spectrum in vastly different ways depending on the system. Specifically, it is
more pronounced in Fe-Ni alloys compared to Fe-Co alloys. In particular, the
magnon spectrum at room temperature in Permalloy (Fe$_{20}$Ni$_{80}$) is found
to be rather diffuse in a large energy interval while in Fe$_{75}$Co$_{25}$ it
forms sharp branches. Fe-Co alloys are very interesting from a technological
point of view due to the combination of large Curie temperatures and very low
calculated Gilbert damping of $\sim$0.0007 at room temperature for Co
concentrations around 20--30\%.",1810.08487v1
2018-10-31,"Comment on ""Optical detection of transverse spin-Seebeck effect in permalloy film using Sagnac interferometer microscopy""","Measuring spin currents and spin accumulations is challenging. This is mainly
because of their small size and the lack of a standard spin detector comparable
to conventional ampere meters or voltage detectors. It is all the more pleasing
to hear about new methods for detecting spin currents and spin accumulations. A
recent example is the paper of McLaughlin et al. [Phys. Rev. B 95, 180401
(2017)], who report novel measurements of the transverse spin-Seebeck effect
(TSSE) in metals by optical means using a Sagnac interferometer microscope.
However, because no standard procedures or reference measurements are available
for verification, critical discussions are crucial for evaluation of such novel
experimental approaches. In our comment, we estimate the size of the effect
observed by McLaughlin et al. To illustrate that the estimated size is
exceptionally large, we use a comparison with another spin-caloritronic effect:
the spin-dependent Seebeck effect. Such a large TSSE is in contradiction with
previous experiments that could not resolve a TSSE signal. Therefore, we
suggest that signal measured by McLaughlin et al. is not or not only caused by
the TSSE.",1810.13220v1
2012-09-04,Microscopic Theory of Magnon-Drag Thermoelectric Transport in Ferromagnetic Metals,"A theoretical study of the magnon-drag Peltier and Seebeck effects in
ferromagnetic metals is presented. A magnon heat current is described
perturbatively from the microscopic viewpoint with respect to electron--magnon
interactions and the electric field. Then, the magnon-drag Peltier coefficient
$\Pi_\MAG$ is obtained as the ratio between the magnon heat current and the
electric charge current. We show that $\Pi_\MAG=C_\MAG T^{5/2}$ at a low
temperature $T$; that the coefficient $C_\MAG$ is proportional to the spin
polarization $P$ of the electric conductivity; and that $P>0$ for $C_\MAG<0$,
but $P<0$ for $C_\MAG>0$. From experimental results for magnon-drag Peltier
effects, we estimate that the strength of the electron--magnon interaction is
about 0.3 eV$\cdot\AA^{3/2}$ for permalloy.",1209.0685v2
2012-09-21,Broadband probing magnetization dynamics of the coupled vortex state permalloy layers in nanopillars,"Broadband magnetization response of coupled vortex state magnetic dots in
layered nanopillars was explored as a function of in-plane magnetic field and
interlayer separation. For dipolarly coupled circular Py(25 nm)/Cu(20 nm)/Py(25
nm) nanopillars of 600 nm diameter, a small in-plane field splits the
eigenfrequencies of azimuthal spin wave modes inducing an abrupt transition
between in-phase and out-of-phase kinds of the low-lying coupled spin wave
modes. The critical field for this splitting is determined by antiparallel
chiralities of the vortices in the layers. Qualitatively similar (although more
gradual) changes occur also in the exchange coupled Py(25 nm)/Cu(1 nm)/Py(25
nm) tri-layer nanopillars. These findings are in qualitative agreement with
micromagnetic dynamic simulations.",1209.4822v1
2014-06-27,Observation of propagating edge spin waves modes,"Broadband magnetization response of equilateral triangular 1000 nm Permalloy
dots has been studied under an in-plane magnetic field, applied parallel
(buckle state) and perpendicular (Y state) to the triangles base. Micromagnetic
simulations identify edge spin waves (E-SWs) in the buckle state as SWs
propagating along the two adjacent edges. These quasi one-dimensional spin
waves emitted by the vertex magnetic charges gradually transform from
propagating to standing due to interference and are weakly affected by dipolar
interdot interaction and variation of the aspect ratio. Spin waves in the Y
state have a two dimensional character. These findings open perspectives for
implementation of the E-SWs in magnonic crystals and thin films.",1406.7186v1
2014-06-27,Spin waves along the edge states,"Spin waves have been studied experimentally and by simulations in 1000 nm
side equilateral triangular Permalloy dots in the Buckle state (B, with
in-plane field along the triangle base) and the Y state (Y, with in-plane field
perpendicular to the base). The excess of exchange energy at the triangles
edges creates channels that allow effective spin wave propagation along the
edges inthe B state. These quasi one-dimensional spin waves emitted by the
vertex magnetic charges gradually transform from propagating to standing due to
interference and(as pointed out by simulations) areweakly affected by
smallvariations of the aspect ratio(from equilateral to isosceles dots) or by
interdot dipolar interaction present in our dot arrays. Spin waves excited in
the Y state have mainly a two-dimensional character.Propagation of the spin
waves along the edge states in triangular dots opens possibilities for creation
of new and versatile spintronic devices.",1406.7200v1
2018-02-12,Spin-orbit torque and spin pumping in YIG/Pt with interfacial insertion layers,"We experimentally investigate spin-orbit torque and spin pumping in
Y$_3$Fe$_5$O$_{12}$(YIG)/Pt bilayers with ultrathin insertion layers at the
interface. An insertion layer of Cu suppresses both spin-orbit torque and spin
pumping, whereas an insertion layer of Ni$_{80}$Fe$_{20}$ (permalloy, Py)
enhances them, in a quantitatively consistent manner with the reciprocity of
the two spin transmission processes. However, we observe a large enhancement of
Gilbert damping with the insertion of Py that cannot be accounted for solely by
spin pumping, suggesting significant spin-memory loss due to the interfacial
magnetic layer. Our findings indicate that the magnetization at the YIG-metal
interface strongly influences the transmission and depolarization of pure spin
current.",1802.03865v3
2018-02-18,New Description of Evolution of Magnetic Phases in Artificial Honeycomb Lattice,"Artificial magnetic honeycomb lattice provides a two-dimensional archetypal
system to explore novel phenomena of geometrically frustrated magnets.
According to theoretical reports, an artificial magnetic honeycomb lattice is
expected to exhibit several phase transitions to unique magnetic states as a
function of reducing temperature. Experimental investigations of permalloy
artificial honeycomb lattice of connected ultra- small elements, ~ 12 nm,
reveal a more complicated behavior. First, upon cooling the sample to
intermediate temperature, T ~ 175 K, the system manifests a non-unique state
where the long range order co-exists with short-range magnetic charge order and
weak spin ice state. Second, at much lower temperature, T ~ 6 K, the long-range
spin solid state exhibits a re-entrant behavior. Both observations are in
direct contrast to the present understanding of this system. New theoretical
approaches are needed to develop a comprehensive formulation of this two
dimensional magnet.",1802.06323v1
2018-02-19,Temperature Dependent Magnetism in Artificial Honeycomb Lattice of Connected Elements,"Artificial magnetic honeycomb lattices are expected to exhibit a broad and
tunable range of novel magnetic phenomena that would be difficult to achieve in
natural materials, such as long-range spin ice, entropy-driven magnetic
charge-ordered state and spin-order due to the spin chirality. Eventually, the
spin correlation is expected to develop into a unique spin solid state density
ground state, manifested by the distribution of the pairs of vortex states of
opposite chirality. Here we report the creation of a new artificial permalloy
honeycomb lattice of ultra-small connecting bonds, with a typical size of
$\simeq$ 12 nm. Detail magnetic and neutron scattering measurements on the
newly fabricated honeycomb lattice demonstrate the evolution of magnetic
correlation as a function of temperature. At low enough temperature, neutron
scattering measurements and micromagnetic simulation suggest the development of
loop state of vortex configuration in this system.",1802.06631v1
2018-08-06,Spin wave dispersion and intensity correlation in width-modulated nanowire arrays: A Brillouin light scattering study,"Using Brillouin light scattering spectroscopy and dynamical matrix method
calculations, we study collective spin waves in dense arrays of periodically
double-side width-modulated Permalloy nanowires. Width modulation is achieved
by creating a sequence of triangular notches on the two parallel nanowire
sides, with a periodicity of p=1000 nm, and tunable relative displacement (D)
of the notches sequence on the two lateral sides. Both symmetric (D=0) and
asymmetric (D= 250 and 500 nm) width-modulated nanowires were investigated. We
have found that the detected modes have Bloch-type character and belong to a
doublet deriving from the splitting of the modes characteristics of the
nanowire with homogeneous width. Interestingly, the amplitude of the magnonic
band, the frequency difference of the doublet, as well as their relative
scattering intensity, can be efficiently controlled by increasing D rather than
having single- or symmetric (D=0) double-side width-modulation.",1808.01732v1
2018-08-10,Ferromagnetic Josephson junctions for cryogenic memory,"Josephson junctions containing ferromagnetic materials have attracted intense
interest both because of their unusual physical properties and because they
have potential application for cryogenic memory. There are two ways to store
information in such a junction: either in the amplitude of the critical current
or in the ground-state phase difference across the junction; the latter is the
topic of this paper. We have recently demonstrated two different ways to
achieve phase control in such junctions: the first uses junctions containing
two magnetic layers in a ""pseudo spin valve"" configuration, while the second
uses junctions containing three magnetic layers with non-collinear
magnetizations. The demonstration devices, however, have not yet been optimized
for use in a large-scale cryogenic memory array. In this paper we outline some
of the issues that must be considered to perform such an optimization, and we
provide a speculative ""phase-diagram"" for the nickel-permalloy spin-valve
system showing which combinations of ferromagnetic layer thicknesses should
produce useful devices.",1808.03639v1
2018-08-28,An Intrinsic Spin Orbit Torque Nano-Oscillator,"Spin torque and spin Hall effect nanooscillators generate high intensity spin
wave auto oscillations on the nanoscale enabling novel microwave applications
in spintronics, magnonics, and neuromorphic computing. For their operation,
these devices require externally generated spin currents either from an
additional ferromagnetic layer or a material with a high spin Hall angle. Here
we demonstrate highly coherent field and current tunable microwave signals from
nanoconstrictions in single 15 and 20 nm thick permalloy layers. Using a
combination of spin torque ferromagnetic resonance measurements, scanning
microBrillouin light scattering microscopy, and micromagnetic simulations, we
identify the autooscillations as emanating from a localized edge mode of the
nanoconstriction driven by spin orbit torques. Our results pave the way for
greatly simplified designs of auto oscillating nanomagnetic systems only
requiring a single ferromagnetic layer.",1808.09330v1
2019-06-01,Coherent ac spin current transmission across an antiferromagnetic CoO insulator,"The recent discovery of spin-current transmission through antiferromagnetic
(AFM) insulating materials opens up unprecedented opportunities for fundamental
physics and spintronics applications. The great mystery currently surrounding
this topic is: how could THz AFM magnons mediate a GHz spin current? This
mis-match of frequencies becomes particularly critical for the case of coherent
ac spin-current, raising the fundamental question of whether a GHz ac
spin-current can ever keep its coherence inside an AFM insulator and so drive
the spin precession of another FM layer coherently? Utilizing element- and
time-resolved x-ray pump-probe measurements on Py/Ag/CoO/Ag/Fe75Co25/MgO(001)
heterostructures, we demonstrate that a coherent GHz ac spin current pumped by
the permalloy (Py) ferromagnetic resonance (FMR) can transmit coherently across
an antiferromagnetic CoO insulating layer to drive a coherent spin precession
of the FM Fe75Co25 layer. Further measurement results favor thermal magnons
rather than evanescent spin waves as the mediator of the coherent ac spin
current in CoO.",1906.00155v1
2019-06-16,Tunable Magnetic Domain Walls for Therapeutic Neuromodulation at Cellular Level: Stimulating Neurons Through Magnetic Nanowires,"Cellular-level neuron stimulation has attracted much attention in the areas
of prevention, diagnosis and treatment of neurological disorders. Herein, we
propose a spintronic neurostimulator based on the domain wall movement inside
stationary magnetic nanowires driven by the spin transfer torque. The
electromotive forces generated by the domain wall motion can serve as highly
localized stimulation signals for neuron cells. Our simulation results show
that the induced electric field from the domain wall motion in permalloy
nanowires can reach up to 14 V/m, which is well above the reported threshold
stimulation signal for clinical applications. The proposed device operates on a
current range of several uA which is 10^3 times lower compared to magnetic
stimulation by microcoils. The duration and amplitude of the stimulating signal
can be controlled by adjusting the applied current density, the geometry of the
nanowire, and the magnetic properties of the nanowire material.",1906.08701v1
2020-04-08,Charge-to-spin conversion efficiency in ferromagnetic nanowires by spin torque ferromagnetic resonance: Reconciling lineshape and linewidth analysis methods,"Spin orbit torques are of great interest for switching the magnetization
direction in nanostructures, moving skyrmions and exciting spin waves. The
standard method of determining their efficiency is by spin torque ferromagnetic
resonance (ST-FMR), a technique that involves analyzing the resonance linewidth
or lineshape. On microstuctures these two analysis methods are quite
consistent. Here we present ST-FMR results on permalloy (Ni$_{80}$Fe$_{20}$)
nanowires -- with widths varying from $150$ to 800 nm -- that show that the
standard model used to analyze the resonance linewidth and lineshape give
different results; the efficiency appears greatly enhanced in nanowires when
the lineshape method is used. A ST-FMR model that properly accounts for the
sample shape is presented and shows much better consistency between the two
methods. Micromagnetic simulations are used to verify the model. These results
and the more accurate nanowire model presented are of importance for
characterizing and optimizing charge-to-spin conversion efficiencies in
nanostructures.",2004.03784v1
2016-03-15,Ordering in rolled-up single-walled ferromagnetic nanomembranes,"Magnetization of soft-ferromagnetic nano- and microtubes of nanometer-thin
walls (a single-widening rolled-up nanomembranes) is theoretically studied
using analytical and numerical approaches including different stress-induced
anisotropies. Within the analytical study, we consider magnetostatic effects
qualitatively, with an effective anisotropy, while they are fully treated in
the micromagnetic simulations (limited to the tubes of submicrometer diameters
however). Basic types of the periodic ordering have been established and their
presence in nanotubes of polycrystalline Permalloy and cobalt has been verified
within the simulations. The domain structure is basically determined by a
material-deposition-induced helical stress or a cooling-induced axial stress
via the volume magnetostriction while it is influenced by the distribution of
magnetic charges as well. Also, it is dependent on the initial state of the
magnetization process.",1603.04883v2
2016-11-20,Selective sensitivity in Kerr microscopy,"A new technique for contrast separation in wide-field magneto-optical Kerr
microscopy is introduced. Utilizing the light from eight light emitting diodes,
guided to the microscope by glass fibers and being switched synchronously with
the camera exposure, domain images with orthogonal in-plane sensitivity can be
displayed simultaneously at real-time and images with pure in-plane or polar
contrast can be obtained. The benefit of this new method of contrast separation
is demonstrated for permalloy films, a NdFeB sinter magnet, and a cobalt
crystal. Moreover, the new technique is shown to strongly enhance the
sensitivity of Kerr microscopy by eliminating parasitic contrast contributions
occurring in conventional setups. A doubling of the in-plane domain contrast
and a sensitivity to Kerr rotations as low as 0.6~mdeg is demonstrated",1612.02027v1
2017-02-16,Extended spin model in atomistic simulations of alloys,"An extended atomistic spin model allowing for studies of the finite
temperature magnetic properties of alloys is proposed. The model is obtained by
extending the Heisenberg Hamiltonian via a parameterization from a first
principles basis, interpolating from both the low temperature ferromagnetic and
the high temperature paramagnetic reference states. This allows us to treat
magnetic systems with varying degree of itinerant character within the model.
Satisfactory agreement with both previous theoretical studies and experiments
are obtained in terms of Curie temperatures and paramagnetic properties. The
proposed model is not restricted to elements but is also applied to binary
alloys, such as the technologically important material Permalloy, where
significant differences in the finite magnetic properties of Fe and Ni magnetic
moments are found. The proposed model strives to find the right compromise
between accuracy and computational feasibility for accurate modeling, even for
complex magnetic alloys and compounds.",1702.05011v1
2017-02-22,Domain wall motion by localized temperature gradients,"Magnetic domain wall (DW) motion induced by a localized Gaussian temperature
profile is studied in a Permalloy nanostrip within the framework of the
stochastic Landau-Lifshitz-Bloch equation. The different contributions to
thermally induced DW motion, entropic torque and magnonic spin transfer torque,
are isolated and compared. The analysis of magnonic spin transfer torque
includes a description of thermally excited magnons in the sample. A third
driving force due to a thermally induced dipolar field is found and described.
Finally, thermally induced DW motion is studied under realistic conditions by
taking into account the edge roughness. The results give quantitative insights
into the different mechanisms responsible for domain wall motion in temperature
gradients and allow for comparison with experimental results.",1702.06725v1
2017-06-11,Absorbing boundary layers for spin wave micromagnetics,"Micromagnetic simulations are used to investigate the effects of different
absorbing boundary layers (ABLs) on spin waves (SWs) reflected from the edges
of a magnetic nano-structure. We define the conditions that a suitable ABL must
fulfill and compare the performance of abrupt, linear, polynomial and tan
hyperbolic damping profiles in the ABL. We first consider normal incidence in a
permalloy stripe and propose a transmission line model to quantify reflections
and calculate the loss introduced into the stripe due to the ABL. We find that
a parabolic damping profile absorbs the SW energy efficiently and has a low
reflection coefficient, thus performing much better than the commonly used
abrupt damping profile. We then investigated SWs that are obliquely incident at
26.6, 45 and 63.4 degrees on the edge of a yttrium-iron-garnet film. The
parabolic damping profile again performs efficiently by showing a high SW
energy transfer to the ABL and a low reflected SW amplitude.",1706.03325v1
2017-10-02,Quantum point contact: a case of spin-resolved electron transport,"The work presents the extended theoretical model of the electrical
conductance in non-magnetic and magnetic nano-size point contacts. The
developed approach describes diffusive, quasi-ballistic, ballistic and quantum
regimes of the spin-resolved conductance. It is based on the electron transport
through metallic junction within approach of the circular constriction. The
model provides unified description of the contact resistance from Maxwell
diffusive through the ballistic to purely quantum transport regimes without any
residual terms depending from the scale. An application are given for
experimental treatment of the golden nanocontacts as a non-magnetic case and
Permalloy nanowire with/without domain wall as example for the magnetic system.
The model of quantum point contact assumes that contact area can be replaced by
the quantum object (i.e. magnetic tunnel junction, narrow domain wall, etc.),
where potential energy profile determine its electrical properties.",1710.00496v1
2017-10-03,Nonlocal electrical detection of spin accumulation generated by Anomalous Hall effects in mesoscopic Ni_81Fe_19 films,"Spin accumulation generated by the anomalous Hall effects (AHE) in mesoscopic
ferromagnetic Ni81Fe19 (permalloy or Py) films is detected electrically by a
nonlocal method. The reciprocal phenomenon, inverse spin Hall effects (ISHE),
can also be generated and detected all-electrically in the same structure. For
accurate quantitative analysis, a series of nonlocal AHE/ISHE structures and
supplementary structures are fabricated on each sample substrate to account for
statistical variations and to accurately determine all essential physical
parameters in-situ. By exploring Py thicknesses of 4 nm, 8 nm, and 12 nm, the
Py spin diffusion length {\lambda}_Py is found to be much shorter than the film
thicknesses. The product of {\lambda}_Py and the Py spin Hall angle {\alpha}_SH
is determined to be independent of thickness and resistivity:
{\alpha}_SH*{\lambda}_Py= (0.066 +/- 0.009) nm at 5 K and (0.041 +/- 0.010) nm
at 295 K. These values are comparable to those obtained from mesoscopic Pt
films.",1710.01186v1
2017-10-25,Collective spin waves in arrays of Permalloy nanowires with single-side periodically modulated width,"We have experimentally and numerically investigated the dispersion of
collective spin waves prop-agating through arrays of longitudinally magnetized
nanowires with periodically modulated width. Two nanowire arrays with
single-side modulation and different periodicity of modulation were studied and
compared to the nanowires with homogeneous width. The spin-wave dispersion,
meas-ured up to the third Brillouin zone of the reciprocal space, revealed the
presence of two dispersive modes for the width-modulated NWs, whose amplitude
of magnonic band depends on the modula-tion periodicity, and a set of
nondispersive modes at higher frequency. These findings are different from
those observed in homogeneous width NWs where only the lowest mode exhibits
sizeable dis-persion. The measured spin-wave dispersion has been satisfactorily
reproduced by means of dynam-ical matrix method. Results presented in this work
are important in view of the possible realization of frequency tunable magnonic
device.",1710.09163v1
2019-03-03,Near-Unity Spin Hall Ratio in Ni$_x$Cu$_{1-x}$ Alloys,"We report a large spin Hall effect in the 3$d$ transition metal alloy
Ni$_x$Cu$_{1-x}$ for $x\in\left\{ 0.3,0.75\right\} $, detected via the
ferromagnetic resonance of a Permalloy (Py = Ni$_{80}$Fe$_{20}$) film deposited
in a bilayer with the alloy. A thickness series at $x$ = 0.6, for which the
alloy is paramagnetic at room temperature, allows us to determine the spin Hall
ratio $\theta_{\rm{SH}}\approx1$, spin diffusion length $\lambda_{\rm{s}}$,
spin mixing conductance $G_{\uparrow\downarrow}$, and damping
$\alpha_{\rm{SML}}$ due to spin memory loss . We compare our results with
similar experiments on Py/Pt bilayers measured using the same method. Ab initio
band structure calculations with disorder and spin-orbit coupling suggest an
intrinsic spin Hall effect in Ni$_x$Cu$_{1-x}$ alloys, although the experiments
here cannot distinguish between extrinsic and intrinsic mechanisms.",1903.00910v2
2019-03-05,Strong Coupling between Microwave Photons and Nanomagnet Magnons,"Coupled microwave photon-magnon hybrid systems offer promising applications
by harnessing various magnon physics. At present, in order to realize high
coupling strength between the two subsystems, bulky ferromagnets with large
spin numbers are utilized, which limits their potential applications for
scalable quantum information processing. In this paper, by enhancing single
spin coupling strength using lithographically defined superconducting
resonators, we report high cooperativities between a resonator mode and a
Kittel mode in nanometer thick Permalloy wires. The on-chip, lithographically
scalable, and superconducting quantum circuit compatible design provides a
direct route towards realizing hybrid quantum systems with nanomagnets, whose
coupling strength can be precisely engineered and dynamic properties can be
controlled by various mechanisms derived from spintronic studies.",1903.01887v3
2019-03-19,Broadband magnetoelastic coupling in magphonic crystals for high-frequency nanoscale spin wave generation,"Spin waves are promising candidates for information carriers in advanced
technology. The interactions between spin waves and acoustic waves in magnetic
nanostructures are of much interest because of their potential application for
spin wave generation, amplification and transduction. We investigate
numerically the dynamics of magnetoelastic excitations in a one-dimensional
magphonic crystal consisting of alternating layers of permalloy and cobalt. We
use the plane wave method and the finite element method for frequency- and
time-domain simulations, respectively. The studied structure is optimized for
hybridization of specific spin-wave and acoustic dispersion branches in the
entire Brillouin zone in a broad frequency range. We show that this type of
periodic structure can be used for efficient generation of high-frequency spin
waves.",1903.08024v1
2019-05-02,Anomalous spin Hall angle of a metallic ferromagnet determined by a multiterminal spin injection/detection device,"We report on the determination of the anomalous spin Hall angle in the
ferromagnetic metal alloy cobalt-iron (Co$_{25}$Fe$_{75}$, CoFe). This is
accomplished by measuring the spin injection/detection efficiency in a
multiterminal device with nanowires of platinum (Pt) and CoFe deposited onto
the magnetic insulator yttrium iron garnet (Y$_3$Fe$_5$O$_{12}$, YIG). Applying
a spin-resistor model to our multiterminal spin transport data, we determine
the magnon conductivity in YIG, the spin conductance at the YIG/CoFe interface
and finally the anomalous spin Hall angle of CoFe as a function of its spin
diffusion length in a single device. Our experiments clearly reveal a negative
anomalous spin Hall angle of the ferromagnetic metal CoFe, but a vanishing
ordinary spin Hall angle. This is in contrast to the results reported for the
ferromagnetic metals Co and permalloy.",1905.00663v1
2019-05-02,Negligible thermal contributions to the spin pumping signal in ferromagnetic metal-Platinum bilayers,"Spin pumping by ferromagnetic resonance is one of the most common technique
to determine spin hall angles, Edelstein lengths or spin diffusion lengths of a
large variety of materials. In recent years, rising concerns have appeared
regarding the interpretation of these experiments, underlining that the signal
could arise purely from thermoelectric effects, rather than from coherent spin
pumping. Here, we propose a method to evaluate the presence or absence of
thermal effects in spin pumping signals, by combining bolometry and spin
pumping by ferromagnetic resonance measurements, and comparing their timescale.
Using a cavity to perform the experiments on Pt\Permalloy and La0.7Sr0.3MnO3\Pt
samples, we conclude on the absence of any measurable thermoelectric
contribution such as the spin Seebeck and anomalous Nernst effects at resonance",1905.00771v2
2020-03-13,Experimental demonstration and analysis of random field effects in ferromagnet/antiferromagnet bilayers,"More than 30 years ago, Malozemoff (Phys. Rev. B 35, 3679 (1987))
hypothesized that exchange interaction at the interface between a ferromagnet
(F) and an antiferromagnet (AF) can act as an effective random field, which can
profoundly affect the magnetic properties of the system. However, until now
this hypothesis has not been directly experimentally tested. We utilize
magnetoelectronic measurements to analyze the effective exchange fields at
Permalloy/CoO interface. Our results cannot be explained in terms of
quasi-uniform effective exchange fields, but are in agreement with the
random-field hypothesis of Malozemoff. The presented approach opens a new route
for the quantitative analysis of effective exchange fields and anisotropies in
magnetic heterostructures for memory, sensing and computing applications.",2003.06295v2
2021-04-22,Theory for electrical detection of the magnon Hall effect induced by dipolar interactions,"We derive the anomalous Hall contributions arising from dipolar interactions
to diffusive spin transport in magnetic insulators. Magnons, the carriers of
angular momentum in these systems, are shown to have a non-zero Berry
curvature, resulting in a measurable Hall effect. For yttrium iron garnet (YIG)
thin films we calculate both the anomalous and magnon spin conductivities. We
show that for a magnetic field perpendicular to the film the anomalous Hall
conductivity is finite. This results in a non-zero Hall signal, which can be
measured experimentally using Permalloy strips arranged like a Hall bar on top
of the YIG thin film. We show that electrical detection and injection of spin
is possible, by solving the resulting diffusion-relaxation equation for a Hall
bar. We predict the experimentally measurable Hall coefficient for a range of
temperatures and magnetic field strengths. Most strikingly, we show that there
is a sign change of the Hall coefficient associated with increasing the
thickness of the film.",2104.11304v1
2021-08-02,Spin Wave Computing using pre-recorded magnetization patterns,"We propose a novel type of a spin wave computing device, based on a bilayer
structure which includes a bias layer, made from a hard magnetic material and a
propagation layer, made from a magnetic material with low damping, for example,
Yttrium Garnet (YiG) or Permalloy. The bias layer maintains a stable
pre-recorded magnetization pattern, generating a bias field with a desired
spatial dependence, which in turn sets the equilibrium magnetization inside the
propagation layer. When an external source applies an RF field or spinwave to
the propagation layer, excited spin waves scatter on the magnetization's
inhomogenuities, resulting in a complex interference behavior. One thus has the
ability to adjust spin wave propagation properties simply by altering the
magnetization in the bias layer. We demonstrate that the phenomenon can be
utilized to perform a variety of computational operations, including Fourier
Transform, Vector-Matrix multiplication and Grover search algorithm, with the
operational parameters exceeding conventional designs by orders of magnitude.",2108.00909v1
2021-10-25,Femtosecond laser comb driven perpendicular standing spin waves,"We study femtosecond laser comb driven sustained and coherent spin wave (SW)
generation in permalloy (Py) films over a thickness range of $d =$ 40--100 nm.
A simple rapid demagnetization model describes the dependence of the observed
SW intensity on laser power for all film thicknesses. In the thicker films we
observe laser comb excited perpendicular standing spin waves up to third order
and to 18 multiples of the 1 GHz laser repetition rate. Our results demonstrate
the versatility of femtosecond combs as contact-less SW point sources over a
wide range of film thickness and type of SW modes.",2110.12947v1
2016-11-09,Effect of nanostructure layout on spin pumping phenomena in antiferromagnet/ nonmagnetic metal/ ferromagnet multilayered stacks,"In this work we focus on magnetic relaxation in Mn$_{80}$Ir$_{20}$(12 nm)/
Cu(6 nm)/ Py($d_\mathrm{F}$) antiferromagnet/Cu/ferromagnet (AFM/Cu/FM)
multilayers with different thickness of the ferromagnetic permalloy layer. An
effective FM-AFM interaction mediated via the conduction electrons in the
nonmagnetic Cu spacer -- the spin-pumping effect -- is detected as an increase
in the linewidth of the ferromagnetic resonance (FMR) spectra and a shift of
the resonant magnetic field. We further find experimentally that the
spin-pumping-induced contribution to the linewidth is inversely proportional to
the thickness of the Py layer. We show that this thickness dependence likely
originates from the dissipative dynamics of the free and localized spins in the
AFM layer. The results obtained could be used for tailoring the dissipative
properties of spintronic devices incorporating antiferromagnetic layers.",1611.02865v1
2017-01-19,Understanding magnetotransport signatures in networks of connected permalloy nanowires,"The change in electrical resistance associated with the application of an
external magnetic field is known as the magnetoresistance (MR). The measured MR
is quite complex in the class of connected networks of single-domain
ferromagnetic nanowires, known as ""artificial spin ice"", due to the
geometrically-induced collective behavior of the nanowire moments. We have
conducted a thorough experimental study of the MR of a connected honeycomb
artificial spin ice, and we present a simulation methodology for understanding
the detailed behavior of this complex correlated magnetic system. Our results
demonstrate that the behavior, even at low magnetic fields, can be
well-described only by including significant contributions from the vertices at
which the legs meet, opening the door to new geometrically-induced MR
phenomena.",1701.05618v1
2017-01-30,Magnetic diode at $T$ = 300 K,"We report the finding of unidirectional electronic properties, analogous to a
semiconductor diode, in two-dimensional artificial permalloy honeycomb lattice
of ultra-small bond, with a typical length of ~ 12 nm. The unidirectional
transport behavior, characterized by the asymmetric colossal enhancement in
differential conductivity at a modest current application of ~ 10-15 $\mu$A,
persists to T = 300 K in honeycomb lattice of thickness ~ 6 nm. The asymmetric
behavior arises without the application of magnetic field. A qualitative
analysis of experimental data suggests the role of magnetic charge or monopoles
in the unusual observations with strong implication for spintronics.",1701.08455v3
2019-01-07,Simultaneous Optical and Electrical Spin-Torque Magnetometry with Stroboscopic Detection of Spin-Precession Phase,"Spin-based coherent information processing and encoding utilize the
precession phase of spins in magnetic materials. However, the detection and
manipulation of spin precession phases remain a major challenge for advanced
spintronic functionalities. By using simultaneous electrical and optical
detection, we demonstrate the direct measurement of the precession phase of
Permalloy ferromagnetic resonance driven by the spin-orbit torques from
adjacent heavy metals. The spin Hall angle of the heavy metals can be
independently determined from concurrent electrical and optical signals. The
stroboscopic optical detection also allows spatially measuring local
spin-torque parameters and the induced ferromagnetic resonance with
comprehensive amplitude and phase information. Our study offers a route towards
future advanced characterizations of spin-torque oscillators, magnonic
circuits, and tunnelling junctions, where measuring the current-induced spin
dynamics of individual nanomagnets are required.",1901.01923v1
2019-01-25,Current-Induced Torques with Dresselhaus Symmetry Due to Resistance Anisotropy in 2D Materials,"We report measurements of current-induced torques in heterostructures of
Permalloy (Py) with TaTe$_2$, a transition-metal dichalcogenide (TMD) material
possessing low crystal symmetry, and observe a torque component with
Dresselhaus symmetry. We suggest that the dominant mechanism for this
Dresselhaus component is not a spin-orbit torque, but rather the Oersted field
arising from a component of current that flows perpendicular to the applied
voltage due to resistance anisotropy within the TaTe$_2$. This type of
transverse current is not present in wires made from a single uniform layer of
a material with resistance anisotropy, but will result whenever a material with
resistance anisotropy is integrated into a heterostructure with materials
having different resistivities, thereby producing a spatially non-uniform
pattern of current flow. This effect will therefore influence measurements in a
wide variety of heterostructures incorporating 2D TMD materials and other
materials with low crystal symmetries.",1901.08908v1
2019-07-15,Tuning edge localized spin waves in magnetic microstripes by proximate magnetic structures,"The propagation of edge localized spin waves (E-SWs) in yttrium iron garnet
(YIG) microstripes with/without the proximate magnetic microstructures is
investigated by micromagnetic simulations. A splitting of the dispersion curve
with the presence of permalloy (Py) stripe is also observed. The E-SWs on the
two edges of YIG stripe have different wavelengths, group velocities, and decay
lengths at the same frequencies. The role of the Py stripe was found to be the
source of the inhomogeneous static dipolar field without dynamic coupling with
YIG. This work opens new perspectives for the design of innovative SW
interference-based logic devices.",1907.06718v1
2019-09-04,Two-axis cavity optomechanical torque characterization of magnetic microstructures,"Significant new functionality is reported for torsion mechanical tools aimed
at full magnetic characterizations of both spin statics and dynamics in micro-
and nanostructures. Specifically, two orthogonal torque directions are
monitored and the results co-analyzed to separate magnetic moment and magnetic
susceptibility contributions to torque, as is desired for characterization of
anisotropic three-dimensional structures. The approach is demonstrated through
application to shape and microstructural disorder-induced magnetic anisotropies
in lithographically patterned permalloy, and will have utility for the
determination of important magnetic thin-film and multilayer properties
including interface anisotropy and exchange bias. The results reflect
remarkable sensitivity of the out-of-plane magnetic torque to the nature of
small edge domains perpendicular to the applied field direction, and also
contain tantalizing indications of direct coupling to spin dynamics at the
frequency of the mechanics.",1909.01949v1
2019-09-09,Modulation of magnon spin transport in a magnetic gate transistor,"We demonstrate a modulation of up to 18% in the magnon spin transport in a
magnetic insulator (Y$_{3}$Fe$_{5}$O$_{12}$, YIG) using a common ferromagnetic
metal (permalloy, Py) as a magnetic control gate. A Py electrode, placed
between two Pt injector and detector electrodes, acts as a magnetic gate in our
prototypical magnon transistor device. By manipulating the magnetization
direction of Py with respect to that of YIG, the transmission of magnons
through the Py|YIG interface can be controlled, resulting in a modulation of
the non-equilibrium magnon density in the YIG channel between the Pt injector
and detector electrodes. This study opens up the possibility of using the
magnetic gating effect for magnon-based spin logic applications.",1909.03775v1
2019-09-11,Determining key spin-orbitronic parameters by means of propagating spin waves,"We characterize spin wave propagation and its modification by an electrical
current in Permalloy(Py)/Pt bilayers with Py thickness between 4 and 20 nm.
First, we analyze the frequency non-reciprocity of surface spin waves and
extract from it the interfacial Dzyaloshinskii-Moriya interaction constant
$D_s$ accounting for an additional contribution due to asymmetric surface
anisotropies. Second, we measure the spin-wave relaxation rate and deduce from
it the Py/Pt spin mixing conductance $g^{\uparrow\downarrow}_{eff}$. Last,
applying a \textit{dc} electrical current, we extract the spin Hall
conductivity $\sigma_{SH}$ from the change of spin wave relaxation rate due to
the spin-Hall spin transfer torque. We obtain a consistent picture of the spin
wave propagation data for different film thicknesses using a single set of
parameters $D_s=0.25$ pJ/m, $g^{\uparrow\downarrow}_{eff} = 3.2\times 10^{19}$
m$^{-2}$ and $\sigma_{SH}=4\times10^{5}$ S/m.",1909.04935v1
2019-10-11,Investigation of spin orbit torque driven dynamics in ferromagnetic heterostructures,"We use time-resolved (TR) measurements based on the polar magneto-optical
Kerr effect (MOKE) to study the magnetization dynamics excited by spin orbit
torques in Py (Permalloy)/Pt and Ta/CoFeB bilayers. The analysis reveals that
the field-like (FL) spin orbit torque (SOT) dominates the amplitude of the
first oscillation cycle of the magnetization precession and the damping-like
(DL) torque determines the final steady-state magnetization. In our bilayer
samples, we have extracted the effective fields, hFL and hDL, of the two SOTs
from the time-resolved magnetization oscillation spectrum. The extracted values
are in good agreement with those extracted from time-integrated DCMOKE
measurements, suggesting that the SOTs do not change at high frequencies. We
also find that the amplitude ratio of the first oscillation to steady state is
linearly proportional to the ratio hFL/hDL. The first oscillation amplitude is
inversely proportional to, whereas the steady state value is independent of,
the applied external field along the current direction.",1910.04945v1
2019-10-16,Spin-Wave frequency division multiplexing in an yttrium iron garnet microstripe magnetized by inhomogeneous field,"Spin waves are promising candidates for information processing and
transmission in a broad frequency range. In the realization of magnonic
devices, the frequency depended division of the spin wave frequencies is a
critical function for parallel information processing. In this work, we
demonstrate a proof-of-concept spin-wave frequency division multiplexing method
by magnetizing a homogenous magnetic microstripe with an inhomogeneous field.
The symmetry breaking additional field is introduced by a permalloy stripe
simply placed in lateral proximity to the waveguide. Spin waves with different
frequencies can propagate independently, simultaneously and separately in space
along the shared waveguide. This work brings new potentials for parallel
information transmission and processing in magnonics.",1910.07136v1
2019-10-30,Understanding Thermal Annealing of Artificial Spin Ice,"We have performed a detailed study of thermal annealing of the moment
configuration in artificial spin ice. Permalloy (Ni$_{80}$Fe$_{20}$) artificial
spin ice samples were examined in the prototypical square ice geometry,
studying annealing as a function of island thickness, island shape, and
annealing temperature and duration. We also measured the Curie temperature as a
function of film thickness, finding that thickness has a strong effect on the
Curie temperature in regimes of relevance to many studies of the dynamics of
artificial spin ice systems. Increasing the interaction energy between island
moments and reducing the energy barrier to flipping the island moments allows
the system to more closely approach the collective low energy state of the
moments upon annealing, suggesting new channels for understanding the
thermalization processes in these important model systems.",1910.14158v1
2019-10-31,Coherent spin pumping in a strongly coupled magnon-magnon hybrid system,"We experimentally identify coherent spin pumping in the magnon-magnon hybrid
modes of permalloy/yttrium iron garnet (Py/YIG) bilayers. Using broadband
ferromagnetic resonance, an ""avoided crossing"" is observed between the uniform
mode of Py and the spin wave mode of YIG due to the fieldlike interfacial
exchange coupling. We also identify additional linewidth suppression and
enhancement for the in-phase and out-of-phase hybrid modes, respectively,
\textcolor{black}{which can be interpreted as concerted dampinglike torque from
spin pumping}. Our analysis predicts inverse proportionality of both fieldlike
and dampinglike torques to the square root of the Py thickness, which
quantitatively agrees with experiments.",1910.14470v2
2020-01-08,Assessing different approaches to ab initio calculations of spin wave stiffness,"Ab initio calculations of the spin wave stiffness constant $D$ for elemental
Fe and Ni performed by different groups in the past have led to values with a
considerable spread of 50-100 %. We present results for the stiffness constant
$D$ of Fe, Ni, and permalloy Fe$_{0.19}$Ni$_{0.81}$ obtained by three different
approaches: (i) by finding the quadratic term coefficient of the power
expansion of the spin wave energy dispersion, (ii) by a damped real-space
summation of weighted exchange coupling constants, and (iii) by integrating the
appropriate expression in reciprocal space. All approaches are implemented by
means of the same Korringa-Kohn-Rostoker (KKR) Green function formalism. We
demonstrate that if properly converged, all procedures yield comparable values,
with uncertainties of 5-10 % remaining. By a careful analysis of the influence
of various technical parameters we estimate the margin of errors for the
stiffness constants evaluated by different approaches and suggest procedures to
minimize the risk of getting incorrect results.",2001.02558v2
2020-05-03,Unconventional spin-orbit torque in transition metal dichalcogenide/ferromagnet bilayers from first-principles calculations,"Motivated by recent observations of unconventional out-of-plane dampinglike
torque in \ch{WTe2}/Permalloy bilayer systems, we calculate the spin-orbit
torque generated in two-dimensional transition metal dichalcogenide
(TMD)-ferromagnet heterostructures using first-principles methods and linear
response theory. Our numerical calculation of spin-orbit torques in
\ch{WTe2}/Co and \ch{MoTe2}/Co heterostructures shows both conventional and
novel dampinglike torkances (torque per electric field) with comparable
magnitude, around $100~\hbar/2e~(\rm \Omega\cdot cm)^{-1}$, for an electric
field applied perpendicular to the mirror plane of the TMD layer. To gain
further insight into the source of dampinglike torque, we compute the spin
current flux between the TMD and Co layers and find good agreement between the
two quantities. This indicates that the conventional picture of dampinglike
spin-orbit torque, whereby the torque results from the spin Hall effect plus
spin transfer torque, largely applies to TMD/Co bilayer systems.",2005.01109v2
2020-06-22,Vortices in Kekulene Molecules,"Kekulene is an aromatic hydrocarbon with formula C48H24 arranged in the shape
of a closed super-ring as shown in Fig. 2. It consists of a sublattice with 48
C atoms with spin 5/2 and a 24 hydrogen sublattice with spin 2. In this
communication, we use Monte Carlo simulations to determine the magnetic
structures present in Kekulene for several temperatures (T) and dipole
anisotropies ({\delta} = D/J). Our results show that there are two regimes at
low temperature separated by a crossover at 2.5 < {\delta}cross < 3.0. For
{\delta} < {\delta}cross the ground state has a unique vortex configuration. In
the region {\delta} > {\delta}cross arrangements of vortices-antivortices
(V-AV) appears. As temperature raises the vortex structure disorders and small
oscillations take over. The importance on synthesizing this molecule grounds in
the possibility of building real planar structures of sizes at least 10 times
smaller than the earlier proposed permalloy nanodots. It is worthy to mention
that Kekulene is a planar structure with atomic thickness, which is a great
advantage compared with other nanomagnetic structures.",2006.12660v1
2020-06-30,Spin-orbit torque magnetization switching in MoTe2/permalloy heterostructures,"The ability to switch magnetic elements by spin-orbit-induced torques has
recently attracted much attention for a path towards high-performance,
non-volatile memories with low power consumption. Realizing efficient
spin-orbit-based switching requires harnessing both new materials and novel
physics to obtain high charge-to-spin conversion efficiencies, thus making the
choice of spin source crucial. Here we report the observation of spin-orbit
torque switching in bilayers consisting of a semimetallic film of 1T'-MoTe2
adjacent to permalloy. Deterministic switching is achieved without external
magnetic fields at room temperature, and the switching occurs with currents one
order of magnitude smaller than those typical in devices using the
best-performing heavy metals. The thickness dependence can be understood if the
interfacial spin-orbit contribution is considered in addition to the bulk spin
Hall effect. Further threefold reduction in the switching current is
demonstrated with resort to dumbbell-shaped magnetic elements. These findings
foretell exciting prospects of using MoTe2 for low-power semimetal material
based spin devices.",2006.16618v1
2020-07-01,Magnetic asymmetry induced anomalous spin-orbit torque in IrMn,"We demonstrate an anomalous spin-orbit torque induced by the broken magnetic
symmetry in the antiferromagnet IrMn. We study the magnetic structure of three
phases of IrMn thin films using neutron diffraction technique. The magnetic
mirror symmetry M' is broken laterally in both L10-IrMn and L12-IrMn3 but not
{\gamma}-IrMn3. We observe an out-of-plane damping-like spin-orbit torque in
both L10-IrMn/permalloy and L12-IrMn3/permalloy bilayers but not in
{\gamma}-IrMn3/permalloy. This is consistent with both the symmetry analysis on
the effects of a broken M' on spin-orbit torque and the theoretical predictions
of the spin Hall effect and the Rashba-Edelstein effect. In addition, the
measured spin-orbit torque efficiencies are 0.61+-0.01, 1.01+-0.03 and
0.80+-0.01 for the L10, L12 and {\gamma} phases, respectively. Our work
highlights the critical roles of the magnetic asymmetry in spin-orbit torque
generation.",2007.00262v1
2020-07-09,Repeated deterministic defect-assisted switching of magnetic vortex core polarity,"Because of its stability, the polarity of a magnetic vortex core (VC) is a
candidate for binary data storage. Switching can be accomplished, e.g, by
driving the VC above a critical velocity $v_c$. Here, we report on controlled
and repeated switching of VC polarity by significantly reducing $v_c$ locally.
We excite vortex dynamics in thin Permalloy disks with a magnetic field pulse,
and map the two-dimensional VC trajectory using time-resolved Kerr microscopy.
In pristine samples, we observe normal gyrotropic motion of the VC. After
laser-induced generation of defects, however, we observe repeated VC reversal
at much-reduced critical velocities as low as 20 m/s. Micromagnetic simulations
reveal how local reduction of exchange coupling can create VC reversal sites
for deterministic VC switching.",2007.05015v1
2020-07-29,Tuning Spin Current Injection at Ferromagnet/Non-Magnet Interfaces by Molecular Design,"There is a growing interest in utilizing the distinctive material properties
of organic semiconductors for spintronic applications. Here, we explore
injection of pure spin current from Permalloy into a small molecule system
based on dinaphtho[2,3-b:2,3-f]thieno[3,2-b]thiophene (DNTT) at ferromagnetic
resonance. The unique tunability of organic materials by molecular design
allows us to study the impact of interfacial properties on the spin injection
efficiency systematically. We show that both, spin injection efficiency at the
interface as well as the spin diffusion length can be tuned sensitively by the
interfacial molecular structure and side chain substitution of the molecule.",2007.16068v1
2021-01-20,Spin-current mediated exchange coupling in MgO-based magnetic tunnel junctions,"Heterostructures composed of ferromagnetic layers that are mutually
interacting through a nonmagnetic spacer are at the core of magnetic sensor and
memory devices. In the present study, layer-resolved ferromagnetic resonance
was used to investigate the coupling between the magnetic layers of a
Co/MgO/Permalloy magnetic tunnel junction. Two magnetic resonance peaks were
observed for both magnetic layers, as probed at the Co and Ni L3 x-ray
absorption edges, showing a strong interlayer interaction through the
insulating MgO barrier. A theoretical model based on the
Landau-Lifshitz-Gilbert-Slonczewski equation was developed, including exchange
coupling and spin pumping between the magnetic layers. Fits to the experimental
data were carried out, both with and without a spin pumping term, and the
goodness of the fit was compared using a likelihood ratio test. This rigorous
statistical approach provides an unambiguous proof of the existence of
interlayer coupling mediated by spin pumping.",2101.08157v1
2021-05-12,Various facets of magnetic charge correlation: Micromagnetic and distorted waveBorn approximation simulations study,"The emergent concept of magnetic charge quasi-particle provides a new realm
to study the evolution of magnetic properties in two-dimensional artificially
frustrated magnets. We report on the exploration of magnetic phases due to
various magnetic charge correlation using the complementary numerical
techniques of micromagnetic and distorted wave Born approximation simulations
in artificial permalloy honeycomb lattice. The honeycomb element length varies
between 10 nm and 100 nm, while the width and thickness are kept within the
single domain limit. In addition to the charge ordered loop state, we observe
disordered charge arrangement, characterized by the random distribution of
$\pm$Q charges, in single domain size honeycomb lattice. As the length of
honeycomb element increases, low multiplicity magnetic charges tend to form
contiguous bands in thinner lattice. Thin honeycomb lattice with 100 nm element
length exhibits a perfect spin ice pattern, which remains unaffected to the
modest increase in the width of element size. We simulate scattering profiles
under the pretext of distorted wave Born approximation formalism for the
micromagnetic phases. The results are expected to provide useful guidance in
the experimental investigation of magnetic phases in artificial honeycomb
magnet.",2105.05753v1
2021-05-24,Phase-resolved electrical detection of coherently coupled magnonic devices,"We demonstrate the electrical detection of magnon-magnon hybrid dynamics in
yttrium iron garnet/permalloy (YIG/Py) thin film bilayer devices. Direct
microwave current injection through the conductive Py layer excites the hybrid
dynamics consisting of the uniform mode of Py and the first standing spin wave
($n=1$) mode of YIG, which are coupled via interfacial exchange. Both the two
hybrid modes, with Py or YIG dominated excitations, can be detected via the
spin rectification signals from the conductive Py layer, providing phase
resolution of the coupled dynamics. The phase characterization is also applied
to a nonlocally excited Py device, revealing the additional phase shift due to
the perpendicular Oersted field. Our results provide a device platform for
exploring hybrid magnonic dynamics and probing their phases, which are crucial
for implementing coherent information processing with magnon excitations",2105.11057v1
2021-07-05,Identifying intrinsic and extrinsic mechanisms of anisotropic magnetoresistance with terahertz probes,"Identifying the intrinsic and extrinsic origins of magneto-transport in
spin-orbit coupled systems has long been a central theme in condensed matter
physics. However, it has been elusive owing to the lack of an appropriate
experimental tool. In this work, using terahertz time-domain spectroscopy, we
unambiguously disentangle the intrinsic and extrinsic contributions to the
anisotropic magnetoresistance (AMR) of a permalloy film. We find that the
scattering-independent intrinsic contribution to AMR is sizable and is as large
as the scattering-dependent extrinsic contribution to AMR. Moreover, the
portion of intrinsic contribution to total AMR increases with increasing
temperature due to the reduction of extrinsic contribution. Further
investigation reveals that the reduction of extrinsic contribution is caused by
the phonon/magnon-induced negative AMR. Our result will stimulate further
researches on other spin-orbit-interaction-induced phenomena for which
identifying the intrinsic and extrinsic contributions is important.",2107.01770v1
2021-07-21,Pinning and gyration dynamics of magnetic vortices revealed by correlative Lorentz and bright-field imaging,"Topological magnetic textures are of great interest in various scientific and
technological fields. To allow for precise control of nanoscale magnetism, it
is of great importance to understand the role of intrinsic defects in the host
material. Here, we use conventional and time-resolved Lorentz microscopy to
study the effect of grain size in polycrystalline permalloy films on the
pinning and gyration orbits of vortex cores inside magnetic nanoislands. To
assess static pinning, we use in-plane magnetic fields to shift the core across
the island while recording its position. This enables us to produce highly
accurate two-dimensional maps of pinning sites. Based on this technique, we can
generate a quantitative map of the pinning potential for the core, which we
identify as being governed by grain boundaries. Furthermore, we investigate the
effects of pinning on the dynamic behavior of the vortex core using
stroboscopic Lorentz microscopy, harnessing a new photoemission source that
accelerates image acquisition by about two orders of magnitude. We find
characteristic changes to the vortex gyration in the form of increased
dissipation and enhanced bistability in samples with larger grains.",2107.10208v1
2021-11-04,Mechanism of magnetic diode in artificial honeycomb lattice,"Spin diode is important prerequisite to practical manifestation of spin
electronics. Yet, a functioning magnetic diode at room temperature is still
illusive. Here, we reveal diode-type phenomena due to magnetic charge mediated
conduction in artificial honeycomb geometry, made of concave shape single
domain permalloy element. We find that honeycomb lattice defies symmetry by
populating vertices with low and high multiplicity magnetic charges, causing
asymmetric magnetization, in applied current of opposite polarity. High
multiplicity units create highly resistive network, thereby inhibiting magnetic
charge dynamics propelled electrical conduction. However, practical realization
of this effect requires modest demagnetization factor in constituting element.
Concave structure fulfills the condition. Subsequently, magnetic diode behavior
emerges across broad thermal range of $T$ = 40K - 300K. The finding is a
departure from the prevailing notion of spin-charge interaction as the sole
guiding principle behind spintronics. Consequently, a new vista, mediated by
magnetic charge interaction, is envisaged for spintronic research",2111.02929v3
2021-11-15,Nonstanding spin waves in a single rectangular permalloy microstrip under uniform magnetic excitation,"Ferromagnetic resonance modes in a single rectangular Ni$_{80}$Fe$_{20}$
microstrip were directly imaged using time-resolved scanning transmission x-ray
microscopy combined with a phase-locked ferromagnetic resonance excitation
scheme and the findings were corroborated by micromagnetic simulations.
Although under uniform excitation in a single confined microstructure typically
standing spin waves are expected, all imaged spin waves showed a nonstanding
character both, at and off resonance, the latter being additionally detected
with microantenna-based ferromagnetic resonance. The effect of the edge quality
on the spin waves was observed in micromagnetic simulations.",2111.07773v3
2022-01-21,Eigenmodes of twisted spin-waves in a thick ferromagnetic nanodisk,"Magnetic vortex is topologically nontrivial and commonly found in
ferromagnetic nanodisks. So far, three classes spin-wave eigenmodes, i.e.,
gyrotropic, azimuthal and radial modes, have been identified in ferromagnetic
nanodisks. Here, using micromagnetic simulation and analytical calculation, we
reveal twisted spin-wave modes in a thick permalloy (Ni0.8Fe0.2) nanodisk. The
twisted spin-waves carry topological charges, which sign depends on the core
polarity of the magnetic vortex in the nanodisk. By applying rotating magnetic
fields at one end of the sample, we observe continuous generation of twisted
spin-waves that have characteristic spiral phase front and carry topological
charge l = 1, -1, 2 and -2. The dispersion relation of twisted spin-waves is
derived analytically and the result is in good agreement with micromagnetic
numerical calculations.",2201.08621v1
2022-01-26,Local ferromagnetic resonance measurements of mesoscopically patterned ferromagnets using deterministically placed nanodiamonds,"Nitrogen-vacancy centers in diamond have recently been established as
effective sensors of the magnetization dynamics in vicinal ferromagnetic
materials. We demonstrate sub-100 nm placement accuracy of
nitrogen-vacancy-containing nanodiamonds and use these as local sensors that
probe optically detected ferromagnetic resonance in mesoscopically patterned
Permalloy islands. These measurements reveal variations in the ferromagnetic
resonance signal at different sites on these structures with distinct behavior
in the edge and the bulk of patterned features. These test measurements
establish an easily implemented approach for spatially targeted measurements of
spin dynamics in mesoscale ferromagnets. In principle, the methodology can also
be extended to local studies of nanoscale ferromagnets such as single magnetic
nanowires and nanoparticles.",2201.10722v1
2022-03-30,Hybrid magnonics for short-wavelength spin waves facilitated by a magnetic heterostructure,"Recent research on hybrid magnonics has been restricted by the long magnon
wavelengths of the ferromagnetic resonance modes. We present an experiment on
the hybridization of 250-nm wavelength magnons with microwave photons in a
multimode magnonic system consists of a planar cavity and a magnetic bilayer.
The coupling between magnon modes in the two magnetic layers, i.e., the uniform
mode in Permalloy (Py) and the perpendicular standing spin waves (PSSWs) in
YIG, serves as an effective means for exciting short-wavelength PSSWs, which is
further hybridized with the photon mode of the microwave resonator. The
demonstrated magnon-photon coupling approaches the superstrong coupling regime,
and can even be achieved near zero bias field.",2203.16310v1
2022-05-13,Micromagnetics of magnetic chemical modulations in soft-magnetic cylindrical nanowires,"We analyze the micromagnetics of short longitudinal modulations of a
high-magnetization material in cylindrical nanowires made of a soft-magnetic
material of lower magnetization such as permalloy, combining magnetic
microscopy, analytical modeling, and micromagnetic simulations. The mismatch of
magnetization induces curling of magnetization around the axis in the
modulations, in an attempt to screen the interfacial magnetic charges. The
curling angle increases with modulation length, until a plateau is reached with
nearly full charge screening for a specific length scale~$\Delta_\mathrm{mod}$,
larger than the dipolar exchange length of any of the two materials. The
curling circulation can be switched by the Oersted field arising from a charge
current with typical magnitude $10^{12} A/m^{2}$ for a diameter of $\sim$100
nm, and reaching a maximum for $\Delta_\mathrm{mod}$.",2205.06705v2
2022-06-28,Collective ferromagnetism of artificial square spin ice,"We have studied the temperature and magnetic field dependence of the total
magnetic moment of large-area permalloy artificial square spin ice arrays. The
temperature dependence and hysteresis behavior are consistent with the coherent
magnetization reversal expected in the Stoner-Wohlfarth model, with clear
deviations due to inter-island interactions at small lattice spacing. Through
micromagnetic simulations, we explore this behavior and demonstrate that the
deviations result from increasingly complex magnetization reversal at small
lattice spacing, induced by inter-island interactions, and depending critically
on details of the island shapes. These results establish new means to tune the
physical properties of artificial spin ice structures and other interacting
nanomagnet systems, such as patterned magnetic media.",2206.14147v1
2022-08-10,Efficient spin-to-charge interconversion in Weyl semimetal TaP at room temperature,"In this paper we present spin-to-charge current conversion properties in the
Weyl semimetal TaP by means of the inverse Rashba-Edelstein effect (IREE) with
the integration of this quantum material with the ferromagnetic metal Permalloy
$(Py=Ni_{81}Fe_{19})$. The spin currents are generated in the Py layer by the
spin pumping effect (SPE) from microwave-driven ferromagnetic resonance and are
detected by a dc voltage along the TaP crystal, at room temperature. We observe
a field-symmetric voltage signal without the contamination of asymmetrical
lines due to spin rectification effects observed in studies using metallic
ferromagnets. The observed voltage is attributed to spin-to-charge current
conversion based on the IREE, made possible by the spin-orbit coupling induced
intrinsically by the bulk band structure of Weyl semimetals. The measured IREE
coefficient ${\lambda}_{IREE}=(0.30 \pm{0.01})$ nm is two orders of magnitude
larger than in graphene and is comparable to or larger than the values reported
for some metallic interfaces and for several topological insulators.",2208.05151v1
2022-09-23,Mapping AC Susceptibility with Quantum Diamond Microscope,"We present a novel technique for determining the microscale AC susceptibility
of magnetic materials. We use magnetic field sensing properties of
nitrogen-vacancy (\ce{NV-}) centers in diamond to gather quantitative data
about the magnetic state of the magnetic material under investigation. In order
to achieve the requisite speed in imaging, a lock-in camera is used to perform
pixel-by-pixel lock-in detection of \ce{NV-} photo-luminescence. In addition, a
secondary sensor is employed to isolate the effect of the excitation field from
fields arising from magnetic structures on \ce{NV-} centers. We demonstrate our
experimental technique by measuring the AC susceptibility of soft permalloy
micro-magnets at excitation frequencies of up to \SI{20}{\hertz} with a spatial
resolution of \SI{1.2}{\micro \meter} and a field of view of \SI{100}{\um}. Our
work paves the way for microscopic measurement of AC susceptibilities of
magnetic materials relevant to physical, biological, and material sciences.",2209.11610v1
2022-10-04,The spin-flop transition in the quasi two dimensional antiferromagnet MnPS3 detected via thermally generated magnon transport,"We present the detection of the spin-flop transition in the antiferromagnetic
van der Waals material MnPS3 via thermally generated nonlocal magnon transport
using permalloy detector strips. The inverse anomalous spin Hall effect has the
unique power to detect an out-of-plane spin accumulation which enables us to
detect magnons with an out-of-plane spin polarization; in contrast to strips of
high spin-orbit material such as Pt which only possess the spin Hall effect and
are only sensitive to an in-plane spin polarization of the spin accumulation.
We show that nonlocal magnon transport is able to measure the spin-flop
transition in the absence of other spurious effects. Our measurements show the
detection of magnons generated by the spin Seebeck effect before and after the
spin-flop transition where the signal reversal of the magnon spin accumulation
agrees with the OOP spin polarization carried by magnon modes before and after
the SF transition.",2210.01418v1
2022-10-13,Effect of interfaces on supercurrent through ferromagnetic materials,"Ferromagnetic Josephson junctions exhibit fascinating physics and the
potential for applications in superconducting logic and memory. The junctions
in a demonstrated superconducting memory prototype contain a magnetic
spin-valve structure with Ni as the fixed layer and NiFe (Permalloy) as the
free layer. However, NiFe exhibits poor supercurrent transmission, which limits
the efficiency of the Josephson junction. We have previously shown that the
supercurrent transmission through a Cu/NiFe/Cu trilayer can be improved by
adding thin layers of Ni between the Cu and NiFe -- possibly due to the
advantageous spin-dependent transport properties of the Cu/Ni interfaces. In
this work we explore this idea further by replacing the Cu/NiFe interfaces with
Pd/NiFe, which also have more desirable transport properties. Compared to the
reference junctions containing Cu/NiFe interfaces, the new junctions exhibit an
increase in the $\pi$-state supercurrent by a factor of 2 along with a change
in the position of the first $0-\pi$ transition.",2210.07151v2
2023-03-09,Phase-resolved optical characterization of nanoscale spin waves,"We study theoretically and experimentally the process of Brillouin light
scattering on an array of silicon disks on a thin Permalloy layer. We show that
phase-resolved Brillouin light scattering microscopy performed on an array of
weakly interacting dielectric nanoresonators can detect nanoscale waves and
measure their dispersion. In our experiment, we were able to map the evolution
of the phase of the spin wave with a wavelength of 209 nm with a precision of 6
nm. These results demonstrate the feasibility of all-optical phase-resolved
characterization of nanoscale spin waves.",2303.05339v1
2023-04-07,A two-color dual-comb system for time-resolved measurements of ultrafast magnetization dynamics using triggerless asynchronous optical sampling,"We report on an Er-doped fiber (EDF)-laser-based dual-comb system that allows
us to perform triggerless asynchronous optical sampling (ASOPS) pump-probe
measurements of ultrafast demagnetization and spin precession in magnetic
materials. Because the oscillation frequencies of the two frequency-comb light
sources are highly stabilized, the pulse-to-pulse timing jitter is sufficiently
suppressed and data accumulation without any trigger signals is possible. To
effectively induce spin precession in ferromagnetic thin films, the spectral
bandwidth of the output of one of the EDF frequency comb sources is broadened
by a highly nonlinear fiber and then amplified at a wavelength of about 1030 nm
by a Yb-doped fiber amplifier. The output of the other frequency comb source is
converted to about 775 nm by second harmonic generation. We used this system to
observe the ultrafast demagnetization and spin precession dynamics on the
picosecond and nanosecond time scales in a permalloy thin film. This
time-domain spectroscopy system is promising for the rapid characterization of
spin-wave generation and propagation dynamics in magnetic materials.",2304.03666v1
2023-04-28,Competing signatures of intersite and interlayer spin transfer in the ultrafast magnetization dynamics,"Optically driven intersite and interlayer spin transfer are individually
known as the fastest processes for manipulating the spin order of magnetic
materials on the sub 100 fs time scale. However, their competing influence on
the ultrafast magnetization dynamics remains unexplored. In our work, we show
that optically induced intersite spin transfer (also known as OISTR) dominates
the ultrafast magnetization dynamics of ferromagnetic alloys such as Permalloy
(Ni80Fe20) only in the absence of interlayer spin transfer into a substrate.
Once interlayer spin transfer is possible, the influence of OISTR is
significantly reduced and interlayer spin transfer dominates the ultrafast
magnetization dynamics. This provides a new approach to control the
magnetization dynamics of alloys on extremely short time scales by fine-tuning
the interlayer spin transfer.",2304.14957v1
2023-04-29,Magnetization precession after non-collinear dual optical excitation,"We investigate the impact of non-collinear dual optical excitation on the
magnetization precession in a permalloy thin film using two ultrashort laser
pulses. By analyzing the magnetization dynamics using time-resolved
magneto-optical methods, we find that the excitation with two ultrashort
optical pulses introduces a long-lasting modification of the electron system
seen as a sizable decrease of the precession frequency and significant increase
(about 25%) of the decay time. Our results reveal that the observed effect
strongly depends on the respective polarization of the two excitation pulses
and the time delay between two optical pulses. Our findings indicate the
occurrence of a new nonlinear opto-spin effect during photoexcitation with two
interfering optical pulses which can potentially be observed in various
materials and at different photon wavelengths.",2305.00259v2
2023-05-01,Coherent and incoherent magnons induced by strong ultrafast demagnetization in thin permalloy films,"Understanding spin dynamics on femto- and picosecond timescales offers new
opportunities for faster and more efficient spintronic devices. Here, we
experimentally investigate the coherent spin dynamics after ultrashort laser
excitation by time-resolved magneto optical Kerr effect (TR-MOKE) in thin
Ni80Fe20 films. We provide a detailed study of the magnetic field and pump
fluence dependence of the coherent precessional dynamics. We show that the
coherent precession lifetime increases with the applied external magnetic field
which cannot be understood by viscous Gilbert damping of the coherent magnons.
Instead, it can be explained by nonlinear magnon interactions and by the change
in the fraction of incoherent magnons. This interpretation is in agreement with
the observed trends of the coherent magnon amplitude and lifetime as a function
of the exciting laser fluence. Our results provide a new insight into the
magnetization relaxation processes in ferromagnetic thin films, which is of
great importance for further spintronic applications.",2305.00814v2
2023-05-13,Suhl Instabilities in Nanoscopic Spheroids,"We simulate the magnetization dynamics of a permalloy spheroid of nanoscopic
size in zero external field, such that both dipolar and exchange interactions
are important. Low excitation power is used to obtain the frequencies and mode
patterns of many normal modes. At higher power, non-linear three and four mode
couplings between magnons carrying orbital angular momentum are observed to
give rise to Suhl instabilities. Suhl's analysis of the selection rules
governing the allowed processes is extended to initial states other than
uniform precession. These rules are studied and confirmed by the simulations.
Both down- and up-conversion are seen as well as three and four-mode processes.
General trends are inferred for preferred instabilities among those that are
allowed, although the thresholds for some instabilities appear to be very high.",2305.07986v1
2023-06-24,Magnon confinement in an all-on-chip YIG cavity resonator using hybrid YIG/Py magnon barriers,"Confining magnons in cavities can introduce new functionalities to magnonic
devices, enabling future magnonic structures to emulate established photonic
and electronic components. As a proof-of-concept, we report magnon confinement
in a lithographically defined all-on-chip YIG cavity created between two
YIG/Permalloy bilayers. We take advantage of the modified magnetic properties
of covered/uncovered YIG film to define on-chip distinct regions with
boundaries capable of confining magnons. We confirm this by measuring multiple
spin pumping voltage peaks in a 400 nm wide platinum strip placed along the
center of the cavity. These peaks coincide with multiple spin-wave resonance
modes calculated for a YIG slab with the corresponding geometry. The
fabrication of micrometer-sized YIG cavities following this technique
represents a new approach to control coherent magnons, while the spin pumping
voltage in a nanometer-sized Pt strip demonstrates to be a non-invasive local
detector of the magnon resonance intensity.",2306.14029v2
2023-07-04,Electrically-controlled hybrid superconductor-ferromagnet cell for high density cryogenic memory,"We report the fabrication and testing, at 4.2 K, of an SISFS device, where S,
F, and I denote a superconductor (Nb), a ferromagnetic material (permalloy),
and an insulator (AlOx), respectively. The F layer covers about one half of the
top electrode of the SIS Josephson junction and is positioned off-center.
Electric current, I _tr, along the S electrode can change the magnetization of
the F layer in such a way that, for one direction of I_tr, a magnetic flux
penetrates the junction perpendicular to the layers, whereas for the opposite
direction, the perpendicular magnetic flux can be removed. In the former state,
the modulation pattern of the Josephson critical current, Ic, in the magnetic
field, H, may acquire minimum near H=0, and restores its usual shape with
maximum in the second state. These states can be used for building a compact
cryogenic memory compatible with single flux quantum electronics.",2307.01433v1
2023-07-29,Single-spin spectroscopy of spontaneous and phase-locked spin torque oscillator dynamics,"We employ N-$V$ magnetometry to measure the stray field dynamics of a
ferromagnetic permalloy nanowire driven by spin-orbit torques. Specifically, we
observe the optically detected magnetic resonance (ODMR) signatures of both
spontaneous DC-driven magnetic oscillations and phase-locking to a second
harmonic drive, developing a simple macrospin model that captures the salient
features. We also observe signatures of dynamics beyond the macrospin model,
including an additional ODMR feature (associated with a second SW mode) and one
mode sapping power from another. Our results provide additional insight into
N-$V$-spin wave coupling mechanisms, and represent a new modality for
sub-wavelength N-$V$ scanned probe microscopy of nanoscale magnetic
oscillators.",2307.16049v1
2023-08-22,Observation of Current-induced Nonlinear Spin Polarization in Pt-Py Bilayers,"We experimentally observe nonlinear spin polarization in metallic bilayers of
platinum and permalloy by means of spin-torque ferromagnetic resonance (ST-FMR)
with the spin-Hall effects. The ST-FMR results under massive dc current
injection contain striking features, which are not caused by extrinsic Joule
heating, but by intrinsic nonlinear spin polarization. The emergence of
nonlinear spin polarization is consistent with observation of unidirectional
spin-Hall magnetoresistance due to magnon generation/annihilation. Moreover,
the magnon generation (annihilation) leads to effective magnetization shrinkage
(expansion) revealed by the ST-FMR measurements. The present study paves a way
to spin-Hall effect based nonlinear spintronic devices as well as
6th-generation mobile communication light sources.",2308.11156v2
2023-11-19,Unraveling oscillations at ferro(para)magnetic and non-collinear antiferromagnetic interfaces,"Here, we show that the ferro(para)magnetic and non-collinear
antiferromagnetic interfaces contribute to oscillating signals observed in the
magnetoresistance. We associate the effect with the fact that the spins on the
surface of IrMn3 produce instability in the surface magnetoresistance of the
material, which is sensitive to the magnetic field. We carried out experiments
using bilayers of IrMn3 under permalloy (Py) and IrMn3 under platinum (Pt). The
oscillations were intensely evident at the Py/IrMn3 interface and less explicit
at the Pt/IrMn3 interface. We carried out the experiments using pulsed current,
with a square pulse width of 1{\mu}s and amplitudes of 20 {\mu}A to 20 mA. The
oscillating signals are proportional to the crystallographic direction of the
material, the ferromagnetism of the material adjacent to IrMn3, and sensitive
to the amplitude of the pulsed current. We believe that observation is a way of
transmitting encoded information through magnetoresistance.",2311.11401v1
2024-03-25,Detection of spin pumping free of rectification and thermal artefacts in molecular-based ferromagnetic insulator V[TCNE]x~2,"The molecular-based ferrimagnetic insulator V(TCNE)x has gained recent
interest for efficient spin-wave excitation due to its low Gilbert damping
ratio a=4E-5, and narrow ferromagnetic resonance linewidth f=1Oe. Here we
report a clean spin pumping signal detected on V(TCNE)x/metal bilayer
structures, free from spin rectification or thermal artifacts. On-chip coupling
of microwave power is achieved via a coplanar waveguide to measure the in-plane
angle-dependence of the inverse spin-Hall effect under ferromagnetic resonance
conditions with respect to a constant external magnetic field. A signature of
pure spin current from V(TCNE)x is observed in both platinum and permalloy
metal layers, demonstrating the utility of V(TCNE)x for magnon spintronics
studies in molecule/solid-state heterostructures.",2403.16429v2
2024-04-04,Direct visualization of local magnetic domain dynamics in a 2D Van der Walls material/ferromagnet interface,"Exploring new strategies for controlling the magnetic domain propagation is
the key to realize ultrafast, high-density domain wall-based memory and logic
devices for next generation computing. These strategies include strain
modulation in multiferroic devices, geometric confinement and area-selective
pinning of domain wall. 2D Van der Waals materials introduce localized
modifications to the interfacial magnetic order, enabling control over the
propagation of magnetic domains. Here, using Lorentz-Transmission Electron
Microscopy (L-TEM) along with the Modified Transport of Intensity equations
(MTIE), we demonstrate controlled domain expansion with in-situ magnetic field
in a ferromagnet (Permalloy, NiFe) interfacing with a 2D Van der Waals material
Graphene (Gr). The Gr/NiFe interface exhibits distinctive domain expansion rate
with magnetic field selectively near the interface which is further analyzed
using micromagnetic simulations. Our findings are crucial for comprehending
direct visualization of interface controlled magnetic domain expansion,
offering insights for developing future domain wall-based technology.",2404.03177v1
2000-01-19,Fermi surface origin of the interrelationship between magnetocrystalline anisotropy and compositional order in transitional metal alloys,"Recently, we outlined a scheme to investigate the effects of compositional
order on the magnetocrystalline anisotropy of alloys from a first-principles
electronic structure point of view \{Phys. Rev. Lett. {\bf 83}, 5369 (1999)\}
and showed that compositional order enhances the magnitude of
magnetocrystalline anisotropy energy (MAE) of Co$_{0.5}$Pt$_{0.5}$ alloy by
some two orders of magnitude as well as affecting the equilibrium magnetization
direction. Here we describe our scheme in detail and present an in-depth study
of the effect by demonstrating its Fermi surface origin. In
Co$_{0.25}$Pt$_{0.75}$ alloy we find that the perfect $ L1_2 $ structure has a
very small MAE whereas imposition of directional order enhances the MAE by two
orders of magnitude. We also present the effect of lattice distortion
(tetragonalization) on the MAE on the same footing and find that in the
Co$_{0.5}$Pt$_{0.5}$ alloy it accounts for only about 20% of the observed MAE,
thus confirming that compositional order is the major player in the enhancement
of MAE. We also examine the directional chemical order that can be produced by
magnetic annealing within the same framework. We extract a Fermi surface
mechanism for the effect in an explicit study of permalloy. Finally, we propose
that the Fermi surface plays a major role in the strong coupling between
magnetocrystalline anisotropy and compositional order in many magnetic alloys.",0001271v1
2002-04-25,Statics and Fast Dynamics of Nanomagnets with Vortex Structure,"Within the framework of the Landau-Lifshitz-Gilbert equation, using permalloy
parameters, we study the statics and dynamics of flat circular magnetic
nano-structures with an in-plane magnetic vortex configuration, putting
particular emphasis on the (planar) vorticity of the magnetic state and on the
(perpendicular) polarisation of the vortex center (which may be shifted with
respect to the center of the circle). These binary degrees of freedom can in
principle be used to manipulate two independent bits of information.
  Studying switching processes induced by in-plane and out-of plane field
pulses we find that it is possible to switch the vorticity of the magnetic dot
on a time scale of 40 ps in strong enough and short enough perpendicular
external field pulses (B_z^ext \approx 0.5 T, duration \approx 40 ps). But for
realistically small values of the Gilbert damping, only the vorticity can be
switched this fast, and it turns out that it is better to dismiss the center of
the circle totally, concentrating on flat 'nano-rings' with an inner radius R_1
and an outer radius R_2. On these 'nano-rings' the vortex state is more stable,
and with respect to the switching of the vorticity these structures have
similar properties as circular dots.",0204541v3
2005-06-09,Magnetoresistance Anisotropy of Polycrystalline Cobalt Films: Geometrical-Size- and Domain-Effects,"The magnetoresistance (MR) of 10 nm to 200 nm thin polycrystalline Co-films,
deposited on glass and insulating Si(100), is studied in fields up to 120 kOe,
aligned along the three principal directions with respect to the current:
longitudinal, transverse (in-plane), and polar (out-of-plane). At technical
saturation, the anisotropic MR (AMR) in polar fields turns out to be up to
twice as large as in transverse fields, which resembles the yet unexplained
geometrical size-effect (GSE), previously reported for Ni- and Permalloy films.
Upon increasing temperature, the polar and transverse AMR's are reduced by
phonon-mediated sd-scattering, but their ratio, i.e. the GSE remains unchanged.
Basing on Potters's theory [Phys.Rev.B 10, 4626(1974)], we associate the GSE
with an anisotropic effect of the spin-orbit interaction on the sd-scattering
of the minority spins due to a film texture. Below magnetic saturation, the
magnitudes and signs of all three MR's depend significantly on the domain
structures depicted by magnetic force microscopy. Based on hysteresis loops and
taking into account the GSE within an effective medium approach, the three MR's
are explained by the different magnetization processes in the domain states.
These reveal the importance of in-plane uniaxial anisotropy and out-of-plane
texture for the thinnest and thickest films, respectively.",0506232v1
2008-11-05,Self organized mode locking effect in superconductor / ferromagnet hybrids,"The vortex dynamics in a low temperature superconductor deposited on top of a
rectangular array of micrometer size permalloy triangles is investigated
experimentally. The rectangular unit cell is such that neighboring triangles
physically touch each other along one direction. This design stabilizes
remanent states which differ from the magnetic vortex state typical of
individual non-interacting triangles. Magnetic Force Microscopy images have
revealed that the magnetic landscape of the template can be switched to an
ordered configuration after magnetizing the sample with an in-plane field. The
ordered phase exhibits a broad flux flow regime with relatively low critical
current and a highly anisotropic response. This behavior is caused by the
spontaneous formation of two separated rows of vortices and antivortices along
each line of connected triangles. The existence of a clear flux flow regime
even for zero external field supports this interpretation. The density of
induced vortex-antivortex pairs is directly obtained using a high frequency
measurement technique which allows us to resolve the discrete motion of
vortices. Strikingly, the presence of vortex-antivortex rows gives rise to a
self organized synchronized motion of vortices which manifests itself as field
independent Shapiro steps in the current-voltage characteristics.",0811.0798v1
2009-02-15,Sudden Critical Current Drops Induced in S/F Structures,"In the search for new physical properties of S/F structures, we have found
that the superconductor critical current can be controlled by the domain state
of the neighboring ferromagnet. The superconductor is a thin wire of thickness
d_{s} ~ 2 xi_{S}. Nb/Co and Nb/Py (Permalloy Ni_{80}Fe_{20}) bilayer structures
were grown with a significant magnetic anisotropy. Critical current
measurements of Nb/Co structures with ferromagnet thickness d_{F} > 30nm show
sudden drops in two very defined steps when the measurements are made along the
hard axes direction (i.e. current track parallel to hard anisotropy axes
direction). These drops disappear when they are made along the easy axis
direction or when the ferromagnet thickness is below 30nm. The drops are
accompanied by vortex flux flow. In addition magnetorestistance measurements
close to Tc show a sharp increase near saturation fields of the ferromagnet.
Similar results are reproduced in Nb/Py bilayer structure with the ferromagnet
thickness d_{F} ~ 50nm along the easy anisotropy axes. These results are
explained as being due to spontaneous vortex formation and flow induced by
Bloch domain walls of the ferromagnet underneath. We argue these Bloch domain
walls produce a 2D vortex-antivortex lattice structure.",0902.2572v2
2009-08-30,Measurement of spin memory lengths in PdNi and PdFe ferromagnetic alloys,"Weakly ferromagnetic alloys are being used by several groups in the study of
superconducting/ferromagnetic hybrid systems. Because spin-flip and spin-orbit
scattering in such alloys disrupt the penetration of pair correlations into the
ferromagnetic material, it is desirable to have a direct measurement of the
spin memory length in such alloys. We have measured the spin memory length at
4.2 K in sputtered Pd0.88Ni0.12 and Pd0.987Fe0.013 alloys using methods based
on current-perpendicular-to-plane giant magnetoresistance. The alloys are
incorporated into hybrid spin valves of various types, and the spin memory
length is determined by fits of the Valet-Fert spin-transport equations to data
of magnetoresistance vs. alloy thickness. For the case of PdNi alloy, the
resulting values of the spin memory length are lsf(PdNi) = 2.8 +/- 0.5 nm and
5.4 +/- 0.6 nm, depending on whether or not the PdNi is exchange biased by an
adjacent Permalloy layer. For PdFe, the spin memory length is somewhat longer,
lsf(PdFe) = 9.6 +/- 2 nm, consistent with earlier measurements indicating lower
spin-orbit scattering in that material. Unfortunately, even the longer spin
memory length in PdFe may not be long enough to facilitate observation of
spin-triplet superconducting correlations predicted to occur in
superconducting/ferromagnetic hybrid systems in the presence of magnetic
inhomogeneity.",0908.4375v1
2010-04-09,Thermally driven spin injection from a ferromagnet into a non-magnetic metal,"Creating, manipulating and detecting spin polarized carriers are the key
elements of spin based electronics. Most practical devices use a perpendicular
geometry in which the spin currents, describing the transport of spin angular
momentum, are accompanied by charge currents. In recent years, new sources of
pure spin currents, i.e., without charge currents, have been demonstrated and
applied. In this paper, we demonstrate a conceptually new source of pure spin
current driven by the flow of heat across a ferromagnetic/non-magnetic metal
(FM/NM) interface. This spin current is generated because the Seebeck
coefficient, which describes the generation of a voltage as a result of a
temperature gradient, is spin dependent in a ferromagnet. For a detailed study
of this new source of spins, it is measured in a non-local lateral geometry. We
developed a 3D model that describes the heat, charge and spin transport in this
geometry which allows us to quantify this process. We obtain a spin Seebeck
coefficient for Permalloy of -3.8 microvolt/Kelvin demonstrating that thermally
driven spin injection is a feasible alternative for electrical spin injection
in, for example, spin transfer torque experiments.",1004.1566v1
2011-03-30,Magnetic domain-wall velocity enhancement induced by a transverse magnetic field,"Spin dynamics of field-driven domain walls (DWs) guided by Permalloy
nanowires are studied by high-speed magneto-optic polarimetry and numerical
simulations. DW velocities and spin configurations are determined as functions
of longitudinal drive field, transverse bias field, and nanowire width.
Nanowires having cross-sectional dimensions large enough to support vortex wall
structures exhibit regions of drive-field strength (at zero bias field) that
have enhanced DW velocity resulting from coupled vortex structures that
suppress oscillatory motion. Factor of ten enhancements of the DW velocity are
observed above the critical longitudinal drive-field (that marks the onset of
oscillatory DW motion) when a transverse bias field is applied. Nanowires
having smaller cross-sectional dimensions that support transverse wall
structures also exhibit a region of higher mobility above the critical field,
and similar transverse-field induced velocity enhancement but with a smaller
enhancement factor. The bias-field enhancement of DW velocity is explained by
numerical simulations of the spin distribution and dynamics within the
propagating DW that reveal dynamic stabilization of coupled vortex structures
and suppression of oscillatory motion in the nanowire conduit resulting in
uniform DW motion at high speed.",1103.6056v1
2011-09-30,Cooling and heating with electron spins: Observation of the spin Peltier effect,"The Peltier coefficient describes the amount of heat that is carried by an
electrical current when it passes through a material. Connecting two materials
with different Peltier coefficients causes a net heat flow towards or away from
the interface, resulting in cooling or heating at the interface - the Peltier
effect. Spintronics describes the transport of charge and angular momentum by
making use of separate spin-up and spin-down channels. Recently, the merger of
thermoelectricity with spintronics has given rise to a novel and rich research
field named spin caloritronics. Here, we report the first direct experimental
observation of refrigeration/heating driven by a spin current, a new spin
thermoelectric effect which we call the spin Peltier effect. The heat flow is
generated by the spin dependency of the Peltier coefficient inside the
ferromagnetic material. We explored the effect in a specifically designed spin
valve pillar structure by measuring the temperature using an electrically
isolated thermocouple. The difference in heat flow between the two magnetic
configurations leads to a change in temperature. With the help of 3-D finite
element modeling, we extracted permalloy spin Peltier coefficients in the range
of -0.9 to -1.3 mV. These results enable magnetic control of heat flow and
provide new functionality for future spintronic devices.",1109.6898v1
2011-12-08,200 ps Vortex Core Reversal by Azimuthal Spin Waves,"Spin wave mediated vortex core reversal has been investigated by
time-resolved scanning transmission X-ray microscopy (STXM). Movies showing the
development of the spin wave and vortex core magnetization dynamics during
unidirectional vortex core reversal could be taken in Permalloy discs, 1.6 \mu
m in diameter and 50 nm thick, during excitation with rotating ac field bursts
of one period duration at 4.5 GHz and with amplitudes up to 4 mT.
Unidirectional switching is achieved by taking advantage of an asymmetry for CW
or CCW excitation caused by the gyrofield. The differences in the magnetization
dynamics due to this asymmetry could be imaged during continuous excitation
with multi-GHz rotating fields. All our experimental results are in good
agreement with micromagnetic simulations.
  In addition, for the sample geometry given above, simulations reveal a lower
limit of about 200 ps for the time of unidirectional vortex core switching,
which cannot be overcome by shortening the excitation length or by increasing
the excitation amplitude. We explain this limitation by the finite time needed
for an energy transfer of the global excitation towards the center of the
sample. Thus smaller samples will allow for much shorter vortex core reversal
times.",1112.1903v1
2012-06-07,Anisotropic magnetothermoelectric power of ferromagnetic thin films,"We compare the behavior of the magnetothermoelectric power (MTEP)in metallic
ferromagnetic thin films of Ni80Fe20 (Permalloy; Py), Co and CrO2 at
temperatures in the range of 100 K to 400 K. In 25 nm thick Py films and 50 nm
thick Co films both the anisotropic magnetoresistance (AMR) and MTEP show a
relative change in resistance and thermoelectric power (TEP) of the order of
0.2% when the magnetic field is reversed, and in both cases there is no
significant change in AMR or MTEP any more after the saturation field has been
reached. Surprisingly, both Py and Co films have opposite MTEP behavior
although both have the same sign for AMR and TEP. The data on 100 nm films of
fully spin-polarized CrO2, grown both on TiO2 and on sapphire, show a different
picture. The MTEP behavior at low fields shows peaks similar to the AMR in
these films, with variations up to 1%. With increasing field both the MR and
the MTEP variations keeps growing, with MTEP showing relative changes of 1.5%
with the thermal gradient along the b-axis and even 20% with the gradient along
the c-axis, with an intermediate value of 3% for the film on sapphire. It
appears that the low-field effects are due to magnetic domain switching, while
the high-field effects are intrinsic to the electronic structure of CrO2.",1206.1527v2
2013-05-04,Effect of perpendicular uniaxial anisotropy on the annihilation fields of magnetic vortices,"The magnetic vortex structure, that is present in several nanoscopic systems,
is stable and can be manipulated through the application of a magnetic field or
a spin polarized current. The size and shape of the core are strongly affected
by the anisotropy, however its role on the core behavior has not yet been
clarified. In the present work we investigate the influence of a perpendicular
anisotropy on the annihilation and shape of magnetic vortex cores in permalloy
disks. We have used both micromagnetic simulations with the OOMMF code, and an
analytical model that assumes that the shape of the core does not change during
the hysteresis cycle, known as the rigid core model, to calculate the
annihilation fields. In both cases we found that the annihilation fields
decrease with increasing perpendicular anisotropy for almost all the structures
investigated. The simulations show that for increasing anisotropy or dot
thickness, or both, the vortex core profile changes its shape, becoming
elongated. For every dot thickness, this change does not depend on the dot
radius, but on the relative distance of the core from the center of the dot.",1305.0942v2
2013-10-28,Precise determination of the spectroscopic g-factor using broadband ferromagnetic resonance spectroscopy,"We demonstrate that the spectroscopic g-factor can be determined with high
precision and accuracy by broadband ferromagnetic resonance measurements and
applying an asymptotic analysis to the data. Spectroscopic data used to
determine the g-factor is always obtained over a finite range of frequencies,
which can result in significant errors in the fitted values of the
spectroscopic g-factor. We show that by applying an asymptotic analysis to
broadband datasets, precise values of the intrinsic g-factor can be determined
with errors well below 1 %, even when the exact form of the Kittel equation
(which describes the relationship between the frequency and resonance field) is
unknown. We demonstrate this methodology with measured data obtained for
sputtered Ni80Fe20 (""Permalloy"") thin films of varied thicknesses, where we
determine the bulk g-factor value to be 2.109 +/- 0.003. Such an approach is
further validated by application to simulated data that includes both noise and
an anisotropy that is not included in the Kittel equation that was used in the
analysis. Finally, we show a correlation of thickness and interface structure
to the magnitude of the asymptotic behavior, which provide insight into
additional mechanisms that may induce deviations from the Kittel equation.",1310.7515v1
2015-12-07,Current Driven Domain Wall Depinning in Notched Permalloy Nanowires,"In this work, we have investigated the domain wall (DW) depinning behavior in
the notched nanowire by a micromagnetic simulation. A transverse domain wall
(TW) was initially positioned at the center of notch and 1 ns length current
pulse was applied to depin the DW with respect to the notch size s and the wire
width variation. We have observed the depinning current density Jd which was a
minimum current to escape DW from the notch. It was found that the depinning
current density decreased as the wire width and the notch size increased. In
the depinning process, we observed the inner structure of DW generally
transformed from TW to anti-vortex wall (AVW). Interestingly, for the case of s
less than 70 nm, AVW formed and depinned closely to the period when current
pulse was active, while for s larger than 70 nm, AVW formed until the current
pulse went to zero and then depinned after flipped TW was formed. It can be
explained that the transformation of DW inner structures were affected by the
spin torque energy and contributed to DW depinning behavior from the notched
nanowires.",1512.01954v1
2016-01-21,Detection of spin pumping from YIG by spin-charge conversion in a Au/Ni$_{80}$Fe$_{20}$ spin-valve structure,"Many experiments have shown the detection of spin-currents driven by
radio-frequency spin pumping from yttrium iron garnet (YIG), by making use of
the inverse spin-Hall effect, which is present in materials with strong
spin-orbit coupling, such as Pt. Here we show that it is also possible to
directly detect the resonance-driven spin-current using Au/permalloy (Py,
Ni$_{80}$Fe$_{20}$) devices, where Py is used as a detector for the spins
pumped across the YIG/Au interface. This detection mechanism is equivalent to
the spin-current detection in metallic non-local spin-valve devices. By finite
element modeling we compare the pumped spin-current from a reference Pt strip
with the detected signals from the Au/Py devices. We find that for one series
of Au/Py devices the calculated spin pumping signals mostly match the
measurements, within 20%, whereas for a second series of devices additional
signals are present which are up to a factor 10 higher than the calculated
signals from spin pumping. We also identify contributions from thermoelectric
effects caused by the resonant (spin-related) and non-resonant heating of the
YIG. Thermocouples are used to investigate the presence of these thermal
effects and to quantify the magnitude of the Spin-(dependent-)Seebeck effect.
Several additional features are observed, which are also discussed.",1601.05605v1
2016-07-22,Magnetic diffuse scattering in artificial kagome spin ice,"The study of magnetic correlations in dipolar-coupled nanomagnet systems with
synchrotron x-ray scattering provides a means to uncover emergent phenomena and
exotic phases, in particular in systems with thermally active magnetic moments.
From the diffuse signal of soft x-ray resonant magnetic scattering, we have
measured magnetic correlations in a highly dynamic artificial kagome spin ice
with sub-70-nm Permalloy nanomagnets. On comparing experimental scattering
patterns with Monte Carlo simulations based on a needle-dipole model, we
conclude that kagome ice I phase correlations exist in our experimental system
even in the presence of moment fluctuations, which is analogous to bulk spin
ice and spin liquid behavior. In addition, we describe the emergence of
quasi-pinch-points in the magnetic diffuse scattering in the kagome ice I
phase. These quasi-pinch-points bear similarities to the fully developed pinch
points with singularities of a magnetic Coulomb phase, and continually evolve
into the latter on lowering the temperature. The possibility to measure
magnetic diffuse scattering with soft x rays opens the way to study magnetic
correlations in a variety of nanomagnetic systems.",1607.06673v1
2016-09-19,Geometrical complexity of the antidots unit cell effect on the spin wave excitations spectra,"We have investigated theoretically (with micromagnetic simulations and plane
wave method) and experimentally (with ferromagnetic resonance and Brillouin
light scattering) three types of antidot lattices (ADLs) based on permalloy
thin films with increased complexity of the unit cell: simple square,
bi-component square and wave-like ADL. We have found that placing a small
additional antidot in the center of the unit cell of the square ADL modify
significantly the spin wave spectrum and its dependence on the orientation of
the in-plane magnetic field. We also check the further changes of spin wave
spectrum resulting from the introduction of air-gaps connecting small and large
antidots. In particular, the presence of small antidots change the dependence
of the frequency of the fundamental mode on the angle of the in-plane applied
magnetic field. The air-gaps strongly discriminates the propagation of spin
waves in two principal direction of ADL lattice, orthogonal to each other. In
spite of these spectral changes, the spatial distribution of the spin wave
amplitude generally preserves some similarities for all three structures. We
also highlighted out the role of defects in the ADL in the observed spectra.
The obtained results can be interesting for the magnonics applications of the
magnonic crystals.",1609.05663v1
2016-09-28,Quantitative separation of the anisotropic magnetothermopower and planar Nernst effect by the rotation of an in-plane thermal gradient,"A thermal gradient as the driving force for spin currents plays a key role in
spin caloritronics. In this field the spin Seebeck effect (SSE) is of major
interest and was investigated in terms of in-plane thermal gradients inducing
perpendicular spin currents (transverse SSE) and out-of-plane thermal gradients
generating parallel spin currents (longitudinal SSE). Up to now all spincaloric
experiments employ a spatially fixed thermal gradient. Thus anisotropic
measurements with respect to well defined crystallographic directions were not
possible. Here we introduce a new experiment that allows not only the in-plane
rotation of the external magnetic field, but also the rotation of an in-plane
thermal gradient controlled by optical temperature detection. As a consequence,
the anisotropic magnetothermopower and the planar Nernst effect in a permalloy
thin film can be measured simultaneously and reveal a phase shift, that allows
the quantitative separation of the thermopower, the anisotropic
magnetothermopower and the planar Nernst effect.",1609.08822v1
2017-12-20,Optical Manipulation of Magnetic Vortex Visualized in situ by 4D Electron Microscopy,"Understanding the fundamental dynamics of topological vortex and antivortex
naturally formed in micro/nanoscale ferromagnetic building blocks under
external perturbations is crucial to magnetic vortex based information
processing and spintronic devices. All previous studies have focused on
magnetic vortex-core switching via external magnetic fields, spin-polarized
currents, or spin waves, which have largely prohibited the investigation of
novel spin configurations that could emerge from the ground states in
ferromagnetic disks and their underlying dynamics. Here, we report in situ
visualization of femtosecond laser quenching induced magnetic vortex change in
various symmetric ferromagnetic Permalloy disks by Lorentz phase imaging using
4D electron microscopy. Besides the switching of magnetic vortex chirality and
polarity, we observed with distinct occurrence frequencies a plenitude of
complex magnetic structures that have never been observed by magnetic field or
current assisted switching. These complex magnetic structures consist of a
number of newly created topological magnetic defects (vortex and antivortex)
strictly conserving the topological winding number, demonstrating the direct
impact of topological invariant on the magnetization dynamics in ferromagnetic
disks. Their spin configurations show mirror or rotation symmetry due to the
geometrical confinement of the disks. Combined micromagnetic simulations with
the experimental observations reveal the underlying magnetization dynamics and
formation mechanism of the optical quenching induced complex magnetic
structures. Their distinct occurrence rates are pertinent to their
formation-growth energetics and pinning effects at the disk edge. Based on
these findings, we propose a paradigm of optical-quenching-assisted fast
switching of vortex cores for the control of magnetic vortex based information
recording and spintronic devices.",1712.07280v1
2017-12-20,Unifying ultrafast demagnetization and intrinsic Gilbert damping in Co/Ni bilayers with electronic relaxation near the Fermi surface,"The ability to controllably manipulate the laser-induced ultrafast magnetic
dynamics is a prerequisite for future high speed spintronic devices. The
optimization of devices requires the controllability of the ultrafast
demagnetization time, , and intrinsic Gilbert damping, . In previous attempts
to establish the relationship between and , the rare-earth doping of a
permalloy film with two different demagnetization mechanism is not a suitable
candidate. Here, we choose Co/Ni bilayers to investigate the relations between
and by means of time-resolved magneto-optical Kerr effect (TRMOKE) via
adjusting the thickness of the Ni layers, and obtain an approximately
proportional relation between these two parameters. The remarkable agreement
between TRMOKE experiment and the prediction of breathing Fermi-surface model
confirms that a large Elliott-Yafet spin-mixing parameter is relevant to the
strong spin-orbital coupling at the Co/Ni interface. More importantly, a
proportional relation between and in such metallic films or heterostructures
with electronic relaxation near Fermi surface suggests the local spin-flip
scattering domains the mechanism of ultrafast demagnetization, otherwise the
spin-current mechanism domains. It is an effective method to distinguish the
dominant contributions to ultrafast magnetic quenching in metallic
heterostructures by investigating both the ultrafast demagnetization time and
Gilbert damping simultaneously. Our work can open a novel avenue to manipulate
the magnitude and efficiency of Terahertz emission in metallic heterostructures
such as the perpendicular magnetic anisotropic Ta/Pt/Co/Ni/Pt/Ta multilayers,
and then it has an immediate implication of the design of high frequency
spintronic devices.",1712.07323v1
2018-01-16,Spin-orbit-torque and magnetic damping in tailored ferromagnetic bilayers,"We study spin-orbit-torque-driven ferromagnetic resonance (FMR) in
ferromagnetic (FM) bilayers, consisting of Co and permalloy (Py), sandwiched
between Pt and MgO layers. We find that the FM layer in contact with the Pt
layers dominantly determines that spin Hall angle, which is consistent with the
spin-transparency model. By contrast, the FMR linewidths are considerably
influenced not only by the spin-pumping effect across the Pt|FM in terface but
also by the spin relaxation such as two-magnon scattering at the FMMgO
interface.The CoMgO interface leads to notably increased FMR linewidths, while
the Py|MgO interface has less effect. This different contribution of each
interface to the spin Hall angel and dissipation parameter suggests that the
stack configuration of Pt|Co|Py|MgO requires less writing energy than
Pt|Py|Co|MgO in spin-orbit-torque-driven magnetic switching. Our approach
offers a promising method to optimize material parameters by engineering either
interfaces in contact with the heavy-metal or the oxide layer.",1801.05131v2
2018-05-31,Comparison of magnetic and structural properties of permalloy Ni80Fe20 grown by dc and high power impulse magnetron sputtering,"We study the microstructure and magnetic properties of Ni80Fe20 thin films
grown by high power impulse magnetron sputtering (HiPIMS), and compare with
films grown by dc magnetron sputtering (dcMS). The films were grown under a
tilt angle of 35{\deg} to identical thickness of 37 nm using both techniques,
at different pressure (0.13-0.73 Pa) and substrate temperature (room
temperature and 100 {\deg}C). All of our films display effective in-plane
uniaxial anisotropy with square easy axis and linear hard axis magnetization
traces. X-ray diffraction reveals that there is very little change in grain
size within the pressure and temperature ranges explored. However, variations
in film density, obtained by X-ray reflectivity measurements, with pressure
have a significant effect on magnetic properties such as anisotropy field (Hk)
and coercivity (Hc). Depositions where adatom energy is high produce dense
films, while low adatom energy results in void-rich films with higher Hk and
Hc. The latter applies to our dcMS deposited films at room temperature and high
pressure. However, the HiPIMS deposition method gives higher adatom energy than
the dcMS and results in dense films with low Hk and Hc. The surface roughness
is found to increase with increased pressure, in all cases, however it showed
negligible contribution to the increase in Hk and Hc.",1805.12580v2
2019-11-29,Real space observation of magnon interaction with driven space-time crystals,"The concept of Space-Time Crystals (STC), i.e. translational symmetry
breaking in time and space, was recently proposed and experimentally
demonstrated for quantum systems. Here, we transfer this concept to magnons and
experimentally demonstrate a driven STC at room temperature. The STC is
realized by strong homogeneous micro-wave pumping of a micron-sized permalloy
(Py) stripe and is directly imaged by Scanning Transmission X-ray Microscopy
(STXM). For a fundamental understanding of the formation of the STC,
micromagnetic simulations are carefully adapted to model the experimental
findings. Beyond the mere generation of a STC, we observe the formation of a
magnonic band structure due to back folding of modes at the STC's Brillouin
zone boundaries. We show interactions of magnons with the STC that appear as
lattice scattering. This results in the generation of ultra short spin waves
down to 100 nm wavelength that cannot be described by classical dispersion
relations for linear spin wave excitations. We expect that room temperature
STCs will be a useful tool to investigate non-linear wave physics, as they can
be easily generated and manipulated to control their spatial and temporal band
structure.",1911.13192v1
2018-10-11,"Magnons in a Quasicrystal: Propagation, Localization and Extinction of Spin Waves in Fibonacci Structures","Magnonic quasicrystals exceed the possibilities of spin wave (SW)
manipulation offered by regular magnonic crystals, because of their more
complex SW spectra with fractal characteristics. Here, we report the direct
x-ray microscopic observation of propagating SWs in a magnonic quasicrystal,
consisting of dipolarly coupled permalloy nanowires arranged in a
one-dimensional Fibonacci sequence. SWs from the first and second band as well
as evanescent waves from the band gap between them are imaged. Moreover,
additional mini-band gaps in the spectrum are demonstrated, directly indicating
an influence of the quasiperiodicity of the system. The experimental results
are interpreted using numerical calculations and we deduce a simple model to
estimate the frequency position of the magnonic gaps in quasiperiodic
structures. The demonstrated features of SW spectra in one-dimensional magnonic
quasicrystals allows utilizing this class of metamaterials for magnonics and
makes them an ideal basis for future applications.",1810.04931v2
2018-02-18,Spin Solid versus Magnetic Charge Ordered State in Artificial Honeycomb Lattice of Connected Elements,"The nature of magnetic correlation at low temperature in two-dimensional
artificial magnetic honeycomb lattice is a strongly debated issue. While
theoretical researches suggest that the system will develop a novel zero
entropy spin solid state as T --> 0 K, a confirmation to this effect in
artificial honeycomb lattice of connected elements is lacking. We report on the
investigation of magnetic correlation in newly designed artificial permalloy
honeycomb lattice of ultra-small elements, with a typical length of ~ 12 nm,
using neutron scattering measurements and temperature dependent micromagnetic
simulations. Numerical modeling of the polarized neutron reflectometry data
elucidates the temperature dependent evolution of spin correlation in this
system. As temperature reduces to ~ 7 K, the system tends to develop novel spin
solid state, manifested by the alternating distribution of magnetic vortex
loops of opposite chiralities. Experimental results are complemented by
temperature dependent micromagnetic simulations that confirm the dominance of
spin solid state over local magnetic charge ordered state in the artificial
honeycomb lattice with connected elements. Our results enable a direct
investigation of novel spin solid correlation in the connected honeycomb
geometry of two-dimensional artificial structure.",1802.06322v1
2018-12-02,Direct detection of induced magnetic moment and efficient spin-to-charge conversion in graphene/ferromagnetic structures,"This article shows that the spin-to-charge current conversion in single-layer
graphene (SLG) by means of the inverse Rashba-Edelstein effect (IREE) is made
possible with the integration of this remarkable 2D-material with the unique
ferrimagnetic insulator yttrium iron garnet (YIG = $Y_{3}Fe_{5}O_{12}$) as well
as with the ferromagnetic metal permalloy (Py = $Ni_{81}Sb_{19}$). By means of
X-ray absorption spectroscopy (XAS) and magnetic circular dichroism (XMCD)
techniques, we show that the carbon atoms of the SLG acquires an induced
magnetic moment due to the proximity effect with the magnetic layer. The spin
currents are generated in the magnetic layer by spin pumping from microwave
driven ferromagnetic resonance and are detected by a dc voltage along the
graphene layer, at room temperature. The spin-to-charge current conversion,
occurring at the graphene layer, is explained by the extrinsic spin-orbit
interaction (SOI) induced by the proximity effect with the ferromagnetic layer.
The results obtained for the SLG/YIG and SLG/Py systems confirm very similar
values for the IREE parameter, which are larger than the values reported in
previous studies for SLG. We also report systematic investigations of the
electronic and magnetic properties of the SLG/YIG by means of scanning
tunneling microscopy (STM).",1812.00455v1
2018-12-13,Scaling of intrinsic domain wall magneto-resistance with confinement in electromigrated nanocontacts,"In this work we study the evolution of intrinsic domain wall
magnetoresistance (DWMR) with domain wall confinement. Clean permalloy notched
half-ring nanocontacts are fabricated using a special ultra-high vacuum
electromigration procedure to tailor the size of the wire in-situ and through
the resulting domain wall confinement we tailor the domain wall width from a
few tens of nm down to a few nm. Through measurements of the dependence of the
resistance with respect to the applied field direction we extract the
contribution of a single domain wall to the MR of the device, as a function of
the domain wall width in the confining potential at the notch. In this size
range, an intrinsic positive MR is found, which dominates over anisotropic MR,
as confirmed by comparison to micromagnetic simulations. Moreover, the MR is
found to scale monotonically with the size of the domain wall, $\delta_{DW}$,
as 1/$\delta_{DW}^b$, with $b=2.31\pm 0.39 $. The experimental result is
supported by quantum-mechanical transport simulations based on ab-initio
density functional theory calculations.",1812.05689v1
2020-08-29,Unveiling the polarity of the spin-to-charge current conversion in $Bi_2Se_3$,"We report an investigation of the spin- to charge-current conversion in
sputter-deposited films of topological insulator $Bi_2Se_{3}$ onto single
crystalline layers of YIG $(Y_{3}Fe_{5}O_{12})$ and polycrystalline films of
Permalloy $(Py = Ni_{81}Fe_{19})$. Pure spin current was injected into the
$Bi_{2}Se_{3}$ layer by means of the spin pumping process in which the spin
precession is obtained by exciting the ferromagnetic resonance of the
ferromagnetic film. The spin-current to charge-current conversion, occurring at
the $Bi_{2}Se_{3}/$ferromagnet interface, was attribute to the inverse
Rashba-Edelstein effect (IREE). By analyzing the data as a function of the
$Bi_{2}Se_{3}$ thickness we calculated the IREE length used to characterize the
efficiency of the conversion process and found that 1.2 pm
$\leq|{\lambda}_{IREE}|\leq$ 2.2 pm. These results support the fact that the
surface states of $Bi_{2}Se_{3}$ have a dominant role in the spin-charge
conversion process, and the mechanism based on the spin diffusion process plays
a secondary role. We also discovered that the spin- to charge-current mechanism
in $Bi_{2}Se_{3}$ has the same polarity as the one in Ta, which is the opposite
to the one in Pt. The combination of the magnetic properties of YIG and Py,
with strong spin-orbit coupling and dissipationless surface states
topologically protected of $Bi_{2}Se_{3}$ might lead to spintronic devices with
fast and efficient spin-charge conversion.",2008.12900v1
2016-03-17,Proposal of a micromagnetic standard problem for ferromagnetic resonance simulations,"Nowadays, micromagnetic simulations are a common tool for studying a wide
range of different magnetic phenomena, including the ferromagnetic resonance. A
technique for evaluating reliability and validity of different micromagnetic
simulation tools is the simulation of proposed standard problems. We propose a
new standard problem by providing a detailed specification and analysis of a
sufficiently simple problem. By analyzing the magnetization dynamics in a thin
permalloy square sample, triggered by a well defined excitation, we obtain the
ferromagnetic resonance spectrum and identify the resonance modes via Fourier
transform. Simulations are performed using both finite difference and finite
element numerical methods, with \textsf{OOMMF} and \textsf{Nmag} simulators,
respectively. We report the effects of initial conditions and simulation
parameters on the character of the observed resonance modes for this standard
problem. We provide detailed instructions and code to assist in using the
results for evaluation of new simulator tools, and to help with numerical
calculation of ferromagnetic resonance spectra and modes in general.",1603.05419v1
2017-01-09,Spin-Wave Modes in Transition from a Thin Film to a Full Magnonic Crystal,"Spin-wave modes are studied under the gradual transition from a flat thin
film to a 'full' (one-dimensional) magnonic crystal. For this purpose, the
surface of a pre-patterned 36.8 nm thin permalloy film was sequentially ion
milled resulting in magnonic hybrid structures, referred to as
surface-modulated magnonic crystals, with increasing modulation depth. After
each etching step, ferromagnetic resonance measurements were performed yielding
the spin-wave resonance modes in backward-volume and Damon-Eshbach geometry.
The spin-wave spectra of these hybrid systems reveal an even larger variety of
spin-wave states compared to the 'full' magnonic crystal. The measurements are
corroborated by quasi-analytical theory and micromagnetic simulations in order
to study the changing spin-wave mode character employing spin-wave mode
profiles. In backward-volume geometry, a gradual transition from the uniform
mode in the film limit to a fundamental mode in the thin part of the magnonic
crystal was observed. Equivalently, the first and the second film modes are
transform into a center and an edge mode of the thick part of the magnonic
crystal. Simple transition rules from the $n^{\mathrm{th}}$ film mode to the
$m^{\mathrm{th}}$ mode in the 'full' magnonic crystal are formulated unraveling
the complex mode structure particularly in the backward-volume geometry. An
analogous analysis was performed in the Damon-Eshbach geometry.",1702.05675v3
2017-10-17,Dirac-Surface-State-Dominated Spin to Charge Current Conversion in the Topological Insulator $(Bi_{0.22}Sb_{0.78})_2Te_3$ Films at Room Temperature,"We report the spin to charge current conversation in an intrinsic topological
insulator (TI) $(Bi_{0.22}Sb_{0.78})_2Te_3$ film at room temperature. The spin
currents are generated in a thin layer of permalloy (Py) by two different
processes, spin pumping (SPE) and spin Seebeck effects (SSE). In the first we
use microwave-driven ferromagnetic resonance of the Py film to generate a SPE
spin current that is injected into the TI $(Bi_{0.22}Sb_{0.78})_2Te_3$ layer in
direct contact with Py. In the second we use the SSE in the longitudinal
configuration in Py without contamination by the Nernst effect made possible
with a thin NiO layer between the Py and $(Bi_{0.22}Sb_{0.78})_2Te_3$ layers.
The spin-to-charge current conversion is attributed to the inverse Edelstein
effect (IEE) made possible by the spin-momentum locking in the electron Fermi
contours due to the Rashba field. The measurements by the two techniques yield
very similar values for the IEE parameter, which are larger than the reported
values in the previous studies on topological insulators.",1710.06224v1
2019-03-13,"Epitaxial growth, structural characterization and exchange bias of non-collinear antiferromagnetic Mn$_{3}$Ir thin films","Antiferromagnetic materials are of great interest for spintronics. Here we
present a comprehensive study of the growth, structural characterization, and
resulting magnetic properties of thin films of the non-collinear
antiferromagnet Mn$_{3}$Ir. Using epitaxial engineering on MgO (001) and
Al$_{2}$O$_{3}$ (0001) single crystal substrates, we control the growth of
cubic ${\gamma}$-Mn$_{3}$Ir in both (001) and (111) crystal orientations, and
discuss the optimization of growth conditions to achieve high-quality crystal
structures with low surface roughness. Exchange bias is studied in bilayers,
with exchange bias fields as large as -29 mT (equivalent to a unidirectional
anisotropy constant of 11.5 nJ cm$^{-2}$) measured in Mn$_{3}$Ir (111) /
permalloy heterostructures at room temperature. In addition, a distinct
dependence of blocking temperature on in-plane crystallographic direction in
Mn$_{3}$Ir (001) / Py bilayers is observed. These findings are discussed in the
context of chiral antiferromagnetic domain structures, and will inform progress
towards topological antiferromagnetic spintronic devices.",1903.05539v1
2019-05-16,Element-specific visualization of dynamic magnetic coupling in a Co/Py bilayer microstructure,"We present the element-specific and time resolved visualization of uniform
ferromagnetic resonance excitations of a Permalloy (Py) disk - Cobalt (Co)
stripe bilayer microstructure. The transverse high frequency component of the
resonantly excited magnetization is sampled in the ps regime by a combination
of ferromagnetic resonance (FMR) and scanning transmission X-ray microscopy
(STXM- FMR) recording snapshots of the local magnetization precession of Py and
Co with nanometer spatial resolution. The approach allows us to individually
image the resonant dynamic response of each element, and we find that angular
momentum is transferred from the Py disk to the Co stripe and vice versa at
their respective resonances. The integral (cavity) FMR spectrum of our sample
shows an unexpected additional third resonance. This resonance is observed in
the STXM-FMR experiments as well and our microscopic findings suggest that it
is governed by magnetic exchange between Py and Co, showing for the Co stripe a
difference in relative phase of the magnetization due to stray field influence.",1905.06772v6
2021-10-04,Separation of Artifacts from Spin-Torque Ferromagnetic Resonance Measurements of Spin-Orbit Torque for the Low-Symmetry van der Waals Semi-Metal ZrTe$_\textbf{3}$,"We measure spin-orbit torque generated by exfoliated layers of the
low-symmetry semi-metal ZrTe$_3$ using the spin-torque ferromagnetic resonance
(ST-FMR) technique. When the ZrTe$_3$ has a thickness greater than about 10 nm,
artifacts due to spin pumping and/or resonant heating can cause the standard
ST-FMR analysis to overestimate the true magnitude of the torque efficiency by
as much as a factor of 30, and to indicate incorrectly that the spin-orbit
torque depends strongly on the ZrTe$_3$ layer thickness. Artifact-free
measurements can still be achieved over a substantial thickness range by the
method developed recently to detect ST-FMR signals in the Hall geometry as well
as the longitudinal geometry. ZrTe$_3$/Permalloy samples generate a
conventional in-plane anti-damping spin torque efficiency
$\xi_{||}^{\text{DL}}$ = 0.014 $\pm$ 0.004, and an unconventional in-plane
field-like torque efficiency $|\xi_{||}^{\text{FL}}|$ = 0.003 $\pm$ 0.001. The
out-of-plane anti-damping torque is negligible. We suggest that artifacts
similarly interfere with the standard ST-FMR analysis for other van der Waals
samples thicker than about 10 nm.",2110.01720v2
2008-06-26,Ferromagnetic resonance force spectroscopy of individual sub-micron size samples,"We review how a magnetic resonance force microscope (MRFM) can be applied to
perform ferromagnetic resonance (FMR) spectroscopy of \emph{individual}
sub-micron size samples. We restrict our attention to a thorough study of the
spin-wave eigen-modes excited in permalloy (Py) disks patterned out of the same
43.3 nm thin film. The disks have a diameter of either 1.0 or $0.5 \mu$m and
are quasi-saturated by a perpendicularly applied magnetic field. It is shown
that \emph{quantitative} spectroscopic information can be extracted from the
MRFM measurements. In particular, the data are extensively compared with
complementary approximate models of the dynamical susceptibility: i) a 2D
analytical model, which assumes an homogeneous magnetization dynamics along the
thickness and ii) a full 3D micromagnetic simulation, which assumes an
homogeneous magnetization dynamics below a characteristic length scale $c$ and
which approximates the cylindrical sample volume by a discretized
representation with regular cubic mesh of lateral size $c=3.9$ nm. In our
analysis, the distortions due to a breaking of the axial symmetry are taken
into account, both models incorporating the possibility of a small misalignment
between the applied field and the normal of the disks.",0806.4244v1
2017-04-20,Coupled mode theory for the acoustic wave and spin wave interaction in the magphonic crystals: Propagating magnetoelastic waves,"We have investigated co-directional and contra-directional couplings between
spin wave and acoustic wave in one-dimensional periodic structure (magphonic
crystal). The system consists of two ferromagnetic layers alternating in space.
We have taken into consideration materials commonly used in magnonics: yttrium
iron garnet, CoFeB, permalloy, and cobalt. The coupled mode theory (CMT)
formalism have been successfully implemented to describe magnetoelastic
interaction as a periodic perturbation in the magphonic crystal. The results of
CMT calculations have been verified by more rigorous simulations by
frequency-domain plane wave method and time-domain finite element method. The
presented resonant coupling in the magphonic crystal is an active in-space
mechanism which spatially transfers energy between propagating spin and
acoustic modes, thus creating propagating magnetoelastic wave. We have shown,
that CMT analysis of the magnetoelastic coupling is an useful tool to optimize
and design a spin wave - acoustic wave transducer based on a magphonic
crystals. The effect of spin wave damping has been included to the model to
discuss the efficiency of such a device. Our model shows that it is possible to
obtain forward conversion of the acoustic wave to the spin wave in case of
co-directional coupling and backward conversion in case of contra-directional
coupling.",1704.06118v1
2019-01-03,Calculating spin transport properties from first principles: spin currents,"Local charge and spin currents are evaluated from the solutions of fully
relativistic quantum mechanical scattering calculations for systems that
include temperature-induced lattice and spin disorder as well as intrinsic
alloy disorder. This makes it possible to determine material-specific spin
transport parameters at finite temperatures. Illustrations are given for a
number of important materials and parameters at 300 K. The spin-flip diffusion
length $l_{\rm sf}$ of Pt is determined from the exponential decay of a spin
current injected into a long length of thermally disordered Pt; we find $l_{\rm
sf}^{\rm Pt}= 5.3\pm0.4 \,$nm. For the ferromagnetic substitutional disordered
alloy Permalloy (Py), we inject currents that are fully polarized parallel and
antiparallel to the magnetization and calculate $l_{\rm sf}$ from the
exponential decay of their difference; we find $l_{\rm sf}^{\rm Py}= 2.8 \pm
0.1 \,$nm. The transport polarization $\beta$ is found from the asymptotic
polarization of a charge current in a long length of Py to be $\beta = 0.75 \pm
0.01$. The spin Hall angle $\Theta_{\rm sH}$ is determined from the transverse
spin current induced by the passage of a longitudinal charge current in
thermally disordered Pt; our best estimate is $\Theta_{\rm sH}^{\rm Pt}=4.5 \pm
1 \%$ corresponding to the experimental room temperature bulk resistivity $\rho
=10.8 \mu \Omega \,$cm.",1901.00703v1
2019-04-10,Optical excitation of propagating magnetostatic waves in an epitaxial Galfenol film by an ultrafast magnetic anisotropy change,"Using a time-resolved optically-pumped scanning optical microscopy technique
we demonstrate the laser-driven excitation and propagation of spin waves in a
20-nm film of a ferromagnetic metallic alloy Galfenol epitaxially grown on a
GaAs substrate. In contrast to previous all-optical studies of spin waves we
employ laser-induced thermal changes of magnetocrystalline anisotropy as an
excitation mechanism. A tightly focused 70-fs laser pulse excites packets of
magnetostatic surface waves with a $e^{-1}$ propagation length of 3.4 $\mu$m,
which is comparable with that of permalloy. As a result, laser-driven
magnetostatic spin waves are clearly detectable at distances up to 10 $\mu$m,
which promotes epitaxial Galfenol films to the limited family of materials
suitable for magnonic devices. A pronounced in-plane magnetocrystalline
anisotropy of the Galfenol film offers an additional degree of freedom for
manipulating the spin waves' parameters. Reorientation of an in-plane external
magnetic field relative to the crystallographic axes of the sample tunes the
frequency, amplitude and propagation length of the excited waves.",1904.05171v2
2019-04-30,Tunable ferromagnetic resonance in coupled trilayers with crossed in-plane and perpendicular magnetic anisotropies,"A novel approach to tune the ferromagnetic resonance frequency of a soft
magnetic Ni$_{80}$Fe$_{20}$ (Permalloy = Py) film with in-plane magnetic
anisotropy (IMA) based on the controlled coupling to a hard magnetic
NdCo$_\text{x}$ film with perpendicular magnetic anisotropy (PMA) through a
non-magnetic Al spacer is studied. Using transverse magneto-optical Kerr effect
(TMOKE), alternating gradient magnetometry (AGM) as well as vector network
analyzer ferromagnetic resonance (VNA-FMR) spectroscopy, the influence of both
Co concentration and Al spacer thickness on the static and dynamic magnetic
properties of the coupled IMA/PMA system is investigated. Compared to a single
Py film, two striking effects of the coupling between IMA and PMA layers can be
observed in their FMR spectra. First, there is a significant increase in the
zero-field resonance frequency from 1.3 GHz up to 6.6 GHz, and second, an
additional frequency hysteresis occurs at low magnetic fields applied along the
hard axis. The maximum frequency difference between the frequency branches for
increasing and decreasing magnetic field is as high as 1 GHz, corresponding to
a tunability of about 20% at external fields of typically less than $\pm$70 mT.
The origin of the observed features in the FMR spectra is discussed by means of
magnetization reversal curves.",1904.13275v1
2019-09-13,Monolayer MoS2 field effect transistor with low Schottky barrier height with ferromagnetic metal contacts,"Two-dimensional MoS2 has emerged as promising material for nanoelectronics
and spintronics due to its exotic properties. However, high contact resistance
at metal semiconductor MoS2 interface still remains an open issue. Here, we
report electronic properties of field effect transistor devices using monolayer
MoS2 channels and permalloy (Py) as ferromagnetic (FM) metal contacts.
Monolayer MoS2 channels were directly grown on SiO2/Si substrate via chemical
vapor deposition technique. The increase in current with back gate voltage
shows the tunability of FET characteristics. The Schottky barrier height (SBH)
estimated for Py/MoS2 contacts is found to be +28.8 meV (zero-bias), which is
the smallest value reported so-far for any direct metal (magnetic or
non-magnetic)/monolayer MoS2 contact. With the application of gate voltage (+10
V), SBH shows a drastic reduction down to a value of -6.8 meV. The negative SBH
reveals ohmic behavior of Py/MoS2 contacts. Low SBH with controlled ohmic
nature of FM contacts is a primary requirement for MoS2 based spintronics and
therefore using directly grown MoS2 channels in the present study can pave a
path towards high performance devices for large scale applications.",1909.06014v1
2020-01-24,Dynamics of Spiral Spin Waves in Magnetic Nano-patches: Influence of Thickness and Shape,"We explore the dynamics of spiral spin waves in Permalloy nano-elements with
variable aspect ratio of geometric dimensions, and their potential use as
improved spin wave emitters with no or little biasing field required. Numerical
results show that above a certain thickness, propagating spiral waves can be
obtained in circular and square shaped elements in a flux closure state.
VNA-FMR experiments on 20 nm (thin) and 80 nm (thick) samples confirm two type
of spectra corresponding to different dispersions for thinner and thicker
elements. We show that, for the thicker films, the vortex core region acts as a
source of large amplitude spiral spin waves, which dominate over other modes.
In case of the thinner elements, these modes are critically damped. For
different shapes of the patch, we show that a rich collection of confined
propagating modes can also be excited, modifying the final wave front and
enriching the potential of the nano-dot as a spin wave emitter. We give an
explanation for the intense spiral modes from the perspective of a balance of
dipolar and exchange energies in the sample.",2001.09053v1
2020-02-19,Manipulation of coupling and magnon transport in magnetic metal-insulator hybrid structures,"Ferromagnetic metals and insulators are widely used for generation, control
and detection of magnon spin signals. Most magnonic structures are based
primarily on either magnetic insulators or ferromagnetic metals, while
heterostructures integrating both of them are less explored. Here, by
introducing a Pt/yttrium iron garnet (YIG)/permalloy (Py) hybrid structure
grown on Si substrate, we studied the magnetic coupling and magnon transmission
across the interface of the two magnetic layers. We found that within this
structure, Py and YIG exhibit an antiferromagnetic coupling field as strong as
150 mT, as evidenced by both the vibrating-sample magnetometry and polarized
neutron reflectometry measurements. By controlling individual layer thicknesses
and external fields, we realize parallel and antiparallel magnetization
configurations, which are further utilized to control the magnon current
transmission. We show that a magnon spin valve with an ON/OFF ratio of ~130%
can be realized out of this multilayer structure at room temperature through
both spin pumping and spin Seebeck effect experiments. Thanks to the efficient
control of magnon current and the compatibility with Si technology, the
Pt/YIG/Py hybrid structure could potentially find applications in magnon-based
logic and memory devices.",2002.08266v1
2020-02-20,Study of the spin-pump-induced inverse spin-Hall effect in Bi doped n-type Si,"An inverse spin Hall effect (ISHE) in n-type silicon was observed
experimentally when conduction electrons were scattered on the spin-orbit
potential of bismuth. The spin current in the silicon layer was generated by
excitation of the magnetization precession during ferromagnetic resonance in a
thin permalloy (Py) layer deposited on a Si layer doped by phosphor and
bismuth. From the angular dependences of the dc voltage for different
Py/n-Si:Bi structures aligned along the [011] or [100] crystal axes, we were
able to distinguish the planar Hall effect (PHE) and ISHE contributions. The
ISHE dc voltage signal was proportional to sin{\theta}*sin2{\theta} product for
the structure aligned to the [011] crystal axis and to sin{\theta}*cos2{\theta}
for the [100] direction. In addition, the PHE dc voltage was observed for the
angles corresponded to the sin2{\theta} dependence. It means that for silicon
as a many-valley semiconductor, the scattering of spins due to the spin-orbit
potential induced by shallow donor in n-type material is dependent on the
orientation of the valley axes relative to the direction of the magnetic field.",2002.08639v1
2020-10-07,Correlation of uniaxial magnetic anisotropy axes and principal resistivities in polycrystalline ferromagnetic films,"In the present study, we demonstrate the measurement of resistivity tensor
($\rho$) along the magnetic axes of a polycrystalline film of ferromagnetic
permalloy (Py). To this end, conventional Hall-bar and a more recent extended
van der Pauw methods were utilized for determining 2D $\rho$ in the film plane.
The samples were prepared by normal incidence sputter deposition within an
in-situ magnetic field to induce in-plane uniaxial magnetic anisotropy in the
film. Since $\rho$ might be affected by the internal magnetization of the film,
we performed measurements by rotation of a saturating magnetic field in the
film plane. Both methods indicate that the average resistivity is lower along
the easy axis of the film compared to the hard axis. Since X-ray diffraction
results indicated no dominating texture in the film, we concluded that there is
a correlation between uniaxial magnetic axes and principal resistivity axes.
This is an important finding that allows determining the direction of magnetic
anisotropy axes without magnetometry. The results also verify atomic or pair
ordering to be the origin of uniaxial magnetic anisotropy in the Py since
resistivity is sensitive to the level of order in solids. The extended van der
Pauw utilized here can be easily performed on the as-received samples which is
of practical interest.",2010.03554v3
2020-10-15,Spin injection characteristics of Py/graphene/Pt by gigahertz and terahertz magnetization dynamics driven by femtosecond laser pulse,"Spin transport characteristics of graphene has been extensively studied so
far. The spin transport along c-axis is however reported by rather limited
number of papers. We have studied spin transport characteristics through
graphene along c-axis with permalloy(Py)/graphene(Gr)/Pt by gigahertz (GHz) and
terahertz (THz) magnetization dynamics driven by femtosecond laser pulses. The
relatively simple sample structure does not require electrodes on the sample.
The graphene layer was prepared by chemical vapor deposition and transferred on
Pt film. The quality of graphene layer was characterized by Raman microscopy.
Time resolved magneto-optical Kerr effect is used to characterize gigahertz
magnetization dynamics. Magnetization precession is clearly observed both for
Pt/Py and Pt/Gr/Py. The Gilbert damping constant of Pt/Py was 0.015, indicates
spin pumping effect from Py to Pt. The Gilbert damping constant of Pt/Gr/Py is
found to be 0.011, indicates spin injection is blocked by graphene layer. We
have also performed the measurement of THz emission for Pt/Py and Pt/Gr/Py.
While the THz emission is clearly observed for Pt/Py, a strong reduction of THz
emission is observed for Pt/Gr/Py. With these two different experiments, and
highly anisotropic resistivity of graphite, we conclude that the vertical spin
transport is strongly suppressed by the graphene layer.",2010.07694v1
2020-12-02,Engineered magnetization and exchange stiffness in direct-write Co-Fe nanoelements,"Media with engineered magnetization are essential building blocks in
superconductivity, magnetism and magnon spintronics. However, the established
thin-film and lithographic techniques insufficiently suit the realization of
planar components with on-demand-tailored magnetization in the lateral
dimension. Here, we demonstrate the engineering of the magnetic properties of
CoFe-based nanodisks fabricated by the mask-less technique of focused electron
beam induced deposition (FEBID). The material composition in the nanodisks is
tuned \emph{in-situ} via the e-beam waiting time in the FEBID process and their
post-growth irradiation with Ga ions. The magnetization $M_s$ and exchange
stiffness $A$ of the disks are deduced from perpendicular ferromagnetic
resonance measurements. The achieved $M_s$ variation in the broad range from
$720$ emu/cm$^3$ to $1430$ emu/cm$^3$ continuously bridges the gap between the
$M_s$ values of such widely used magnonic materials as permalloy and CoFeB. The
presented approach paves a way towards nanoscale 2D and 3D systems with
controllable and space-varied magnetic properties.",2012.01481v1
2021-01-18,Systematic electrochemical etching of various metal tips for tunneling spectroscopy and scanning probe microscopy,"Hard point-contact spectroscopy and scanning probe microscopy/spectroscopy
are powerful techniques for investigating materials with strong expandability.
To support these studies, tips with various physical and chemical properties
are required. To ensure the reproducibility of experimental results, the
fabrication of tips should be standardized, and a controllable and convenient
system should be set up. Here a systematic methodology to fabricate various
tips is proposed, involving electrochemical etching reactions. The reaction
parameters fall into four categories: solution, power supply, immersion depth,
and interruption. An etching system was designed and built so that these
parameters could be accurately controlled. With this system, etching parameters
for copper, silver, gold, platinum/iridium alloy, tungsten, lead, niobium,
iron, nickel, cobalt, and permalloy were explored and standardized. Among these
tips, silver and niobium's new recipes were explored and standardized. Optical
and scanning electron microscopies were performed to characterize the sharp
needles. Relevant point-contact experiments were carried out with an etched
silver tip to confirm the suitability of the fabricated tips.",2101.07090v1
2021-02-28,Spin and charge interconversion in Dirac semimetal thin films,"We report spin-to-charge and charge-to-spin conversion at room temperature in
heterostructure devices that interface an archetypal Dirac semimetal, Cd3As2,
with a metallic ferromagnet, Ni0.80Fe0.20 (permalloy). The spin-charge
interconversion is detected by both spin torque ferromagnetic resonance and
ferromagnetic resonance driven spin pumping. Analysis of the symmetric and
anti-symmetric components of the mixing voltage in spin torque ferromagnetic
resonance and the frequency and power dependence of the spin pumping signal
show that the behavior of these processes is consistent with previously
reported spin-charge interconversion mechanisms in heavy metals, topological
insulators, and Weyl semimetals. We find that the efficiency of spin-charge
interconversion in Cd3As2/permalloy bilayers can be comparable to that in heavy
metals. We discuss the underlying mechanisms by comparing our results with
first principles calculations.",2103.00653v1
2021-05-03,Relaxation of a single defect spin by the low-frequency gyrotropic mode of a magnetic vortex,"We excite the gyrotropic mode of a magnetic vortex and observe the resulting
effect on the spin state of a nearby nitrogen-vacancy (NV) defect in diamond.
Thin permalloy disks fabricated on a diamond sample are magnetized in a vortex
state in which the magnetization curls around a central core. The magnetization
dynamics of this configuration are described by a discrete spectrum of confined
magnon modes, as well as a low-frequency gyrotropic mode in which the vortex
core precesses about its equilibrium position. Despite the spin transition
frequencies being far-detuned from the modes of the ferromagnet, we observe
enhanced relaxation of the NV spin when driving the gyrotropic mode. Moreover,
we map the spatial dependence of the interaction between the vortex and the
spin by translating the vortex core within the disk with an applied magnetic
field, resulting in steplike motion as the vortex is pinned and de-pinned. The
strong spin relaxation is observed when the vortex core is within approximately
250 nm of the NV center defect. We attribute this effect to the higher
frequencies in the spectrum of the magnetic fringe field arising from the
soliton-like nature of the gyrotropic mode when driven with sufficiently large
amplitude.",2105.00927v1
2021-05-10,Observation of the Orbital Rashba-Edelstein Magnetoresistance,"We report the observation of magnetoresistance (MR) originating from the
orbital angular momentum transport (OAM) in a Permalloy (Py) / oxidized Cu
(Cu*) heterostructure: the orbital Rashba-Edelstein magnetoresistance. The
angular dependence of the MR depends on the relative angle between the induced
OAM and the magnetization in a similar fashion as the spin Hall
magnetoresistance (SMR). Despite the absence of elements with large spin-orbit
coupling, we find a sizable MR ratio, which is in contrast to the conventional
SMR which requires heavy elements. By varying the thickness of the Cu* layer,
we confirm that the interface is responsible for the MR, suggesting that the
orbital Rashba-Edelstein effect is responsible for the generation of the OAM.
Through Py thickness-dependence studies, we find that the effective values for
the spin diffusion and spin dephasing lengths of Py are significantly larger
than the values measured in Py / Pt bilayers, approximately by the factor of 2
and 4, respectively. This implies that another mechanism beyond the
conventional spin-based scenario is responsible for the MR observed in Py / Cu*
structures originated in a sizeable transport of OAM. Our findings not only
unambiguously demonstrate the current-induced torque without using any heavy
element via the OAM channel but also provide an important clue towards the
microscopic understanding of the role that OAM transport can play for
magnetization dynamics.",2105.04495v2
2021-06-18,The study of active geomagnetic shielding coils system for JUNO,"The Jiangmen Underground Neutrino Observatory (JUNO) is a large liquid
scintillator (LS) detector for neutrino mass ordering and other neutrino
physics research. The detector uses large-size $20$ inches photomultiplier
tubes to detect photons from a liquid scintillator. The large PMTs are
sensitive and easily affected such that the detection efficiency loses about
60$\%$ under the geomagnetic field intensity ($\sim$500 mG). It has a
significantly negative effect on the detector performance, and a compensation
system is necessary for geomagnetic field shielding. As permalloys are easily
rusted in water, a better way for the geomagnetic shielding is to apply an
active compensation coils system. The simulations show that a set of 32
circular coils can meet the experiment requirement. The residual magnetic field
is less than 0.05 G in the Central Detector Photomultiplier Tube (CD-PMT)
region (38.5-39.5 m in diameter). A prototype coil system with a 1.2 m was
built to validate the simulation and the design. The measured data of prototype
and simulation results are consistent with each other, and geomagnetic field
intensity is effectively reduced by coils, verifying the shielding coils system
design for JUNO. This study is expected to provide practical guidance for the
PMT magnetic field shielding for future large-scale detector designs.",2106.09998v3
2021-09-10,Anisotropic MagnetoMemristance,"In the last decade, nanoscale resistive devices with memory have been the
subject of intense study because of their possible use in brain-inspired
computing. However, operational endurance is one of the limiting factors in the
adoption of such technology. For this reason, we discuss the emergence of
current-induced memristance in magnetic materials, known for their durability.
We show analytically and numerically that a single ferromagnetic layer can
possess GHz memristance, due to a combination of two factors: a current-induced
transfer of angular momentum (Zhang-Li torque) and the anisotropic
magnetoresistance (AMR). We term the resulting effect the anisotropic
magneto-memristance (AMM). We connect the AMM to the topology of the
magnetization state, within a simple model of a 1-dimensional annulus-shaped
magnetic layer, confirming the analytical results with micromagnetic
simulations for permalloy. Our results open a new path towards the realization
of single-layer magnetic memristive devices operating at GHz frequencies.",2109.05101v3
2021-09-13,Effect of seed layer thickness on Ta crystalline phase and spin Hall angle,"Heavy metal-ferromagnet bilayer structures have attracted great research
interest for charge-to-spin interconversion. In this work, we have investigated
the effect of the permalloy seed layer on the Ta polycrystalline phase and its
spin Hall angle. Interestingly, for the same deposition rates the crystalline
phase of Ta deposited on Py seed layer strongly depends on the thickness of the
seed layer. We have observed a phase transition from $\alpha$-Ta to
($\alpha$+$\beta$)-Ta while increasing the Py seed layer thickness. The
observed phase transition is attributed to the strain at interface between Py
and Ta layers. Ferromagnetic resonance-based spin pumping studies reveal that
the spin-mixing conductance in the to ($\alpha$+$\beta$)-Ta is relatively
higher as compared to the to $\alpha$-Ta. Spin Hall angles of to $\alpha$-Ta
and to ($\alpha$+$\beta$)-Ta are extracted from inverse spin Hall effect (ISHE)
measurements. Spin Hall angle of the to ($\alpha$+$\beta$)-Ta is estimated to
be $\theta$_SH=-0.15 which is relatively higher than that of to $\alpha$-Ta.
Our systematic results connecting the phase of the Ta with seed layer and its
effect on the efficiency of spin to charge conversion might resolve ambiguities
across various literature and open up new functionalities based on the growth
process for the emerging spintronic devices.",2109.06113v2
2021-11-18,Spin transport at finite temperatures: A first-principles study for ferromagnetic$|$nonmagnetic interfaces,"Symmetry lowering at an interface leads to an enhancement of the effect of
spin-orbit coupling and to a discontinuity of spin currents passing through the
interface. This discontinuity is characterized by a ""spin-memory loss"" (SML)
parameter $\delta$ that has only been determined directly at low temperatures.
Although $\delta$ is believed to be significant in experiments involving
interfaces between ferromagnetic and nonmagnetic metals, especially heavy
metals like Pt, it is more often than not neglected to avoid introducing too
many unknown interface parameters in addition to often poorly known bulk
parameters like the spin-flip diffusion length $l_{\rm sf}$. In this work, we
calculate $\delta$ along with the interface resistance $AR_{\rm I}$ and the
spin-asymmetry parameter $\gamma$ as a function of temperature for Co$|$Pt and
Py$|$Pt interfaces where Py is the ferromagnetic Ni$_{80}$Fe$_{20}$ alloy,
permalloy. We use first-principles scattering theory to calculate the
conductance as well as local charge and spin currents, modeling
temperature-induced disorder with frozen thermal lattice and, for ferromagnetic
materials, spin disorder within the adiabatic approximation. The bulk and
interface parameters are extracted from the spin currents using a Valet-Fert
model generalized to include SML.",2111.09731v1
2022-01-14,Enhancement of supercurrent through ferromagnetic materials by interface engineering,"Josephson junctions containing ferromagnetic materials exhibit interesting
physics and show promise as circuit elements for superconducting logic and
memory. For memory applications, the properties of the junction should be
controllable by changing the magnetic configuration inside the junction. To
achieve good magnetic switching properties, one should choose a soft magnetic
material such as NiFe (permalloy); however, NiFe exhibits poor supercurrent
transmission in Josephson junctions. In this work we put thin layers of Ni on
either side of the NiFe and characterize the magnetic behavior and supercurrent
transmission properties of the Ni/NiFe/Ni trilayers as a function of Ni and
NiFe thicknesses. Using a Ni thickness of 0.4 nm, we find that the magnetic
switching behavior of the trilayers is not severely degraded relative to plain
NiFe, while the maximum supercurrent in the $\pi$-state of the trilayer
Josephson junctions is increased by a factor of four relative to that of NiFe
junctions. We speculate that the supercurrent enhancement is due to the
different spin-dependent transport properties of the Cu/Ni and Cu/NiFe
interfaces.",2201.05444v4
2022-02-04,Three-axis torque investigation of interfacial exchange coupling in a NiFe/CoO bilayer micromagnetic disk,"Micrometer diameter bilayers of NiFe (permalloy, Py) and cobalt oxide (CoO)
deposited on nanomechanical resonators were used to investigate exchange bias
effects. The mechanical compliances of two resonator axes were enhanced by
severing one torsion arm, resulting in a unique three-axis resonator that
responds resonantly to torques generated by a three-axis RF field. Our
technique permits simultaneous measurement of three orthogonal torque
components. Measurements of the anisotropies associated with interfacial
exchange coupling effects have been made. At cryogenic temperatures,
observations of shifted linear hysteresis loops confirmed the presence of
exchange bias from the Py/CoO interface. An in-plane rotating DC bias field was
used to probe in-plane anisotropies through the out-of-plane torque. Training
effects in the rotational hysteresis data were observed and showed that
features due to interfacial coupling did not diminish irrespective of
substantial training of the unidirectional anisotropy. The data from the
rotational hysteresis loops were fit with parameters from a macrospin solution
to the Landau-Lifshitz-Gilbert equation. Each parameter of the exchange bias
model accounts for specific features of the rotational loop.",2202.02386v1
2022-03-30,Tunable magnetically induced transparency spectra in magnon-magnon coupled Y3Fe5O12/permalloy bilayers,"Hybrid magnonic systems host a variety of characteristic quantum phenomena
such as the magnetically-induced transparency (MIT) and Purcell effect, which
are considered useful for future coherent quantum information processing. In
this work, we experimentally demonstrate a tunable MIT effect in the
Y3Fe5O12(YIG)/Permalloy(Py) magnon-magnon coupled system via changing the
magnetic field orientations. By probing the magneto-optic effects of Py and
YIG, we identify clear features of MIT spectra induced by the mode
hybridization between the uniform mode of Py and the perpendicular standing
spin-wave modes of YIG. By changing the external magnetic field orientations,
we observe a tunable coupling strength between the YIG's spin-wave modes and
the Py's uniform mode, upon the application of an out-of-plane magnetic field.
This observation is theoretically interpreted by a geometrical consideration of
the Py and YIG magnetization under the oblique magnetic field even at a
constant interfacial exchange coupling. Our findings show high promise for
investigating tunable coherent phenomena with hybrid magnonic platforms.",2203.16303v1
2022-07-06,Calculating the spin memory loss at Cu$|$metal interfaces from first principles,"The role played by interfaces in metallic multilayers is not only to change
the momenta of incident electrons; their symmetry lowering also results in an
enhancement of the effects of spin-orbit coupling, in particular the flipping
of the spins of conduction electrons. This leads to a significant reduction of
a spin current through a metallic interface that is quantitatively
characterized by a dimensionless parameter $\delta$ called the spin memory loss
(SML) parameter, the interface counterpart of the spin-flip diffusion length
for bulk metals. In this paper we use first-principles scattering calculations
that include temperature-induced lattice and spin disorder to systematically
study three parameters that govern spin transport through metallic interfaces
of Cu with Pt, Pd, Py (permalloy) and Co: the interface resistance, spin
polarization and the SML. The value of $\delta$ for a Cu$|$Pt interface is
found to be comparable to what we recently reported for a Au$|$Pt interface
[Gupta {\it et al.}, Phys. Rev. Lett. 124, 087702 (2020)]. For Cu$|$Py and
Cu$|$Co interfaces, $\delta$ decreases monotonically with increasing
temperature to become negligibly small at room temperature. The calculated
results are in good agreement with currently available experimental values in
the literature. Inserting a Cu layer between Pt and the Py or Co layers
slightly increases the total spin current dissipation at these ""compound""
interfaces.",2207.02395v1
2022-07-08,Measuring the magnon-photon coupling in shaped ferromagnets: tuning of the resonance frequency,"Cavity photons and ferromagnetic spins excitations can exchange information
coherently in hybrid architectures, at speeds set by their mutual coupling
strength. Speed enhancement is usually achieved by optimizing the geometry of
the electromagnetic cavity. Here we show that the geometry of the ferromagnet
plays also an important role, by setting the fundamental frequency of the
magnonic resonator. Using focused ion beam patterning, we vary the aspect ratio
of different Permalloy samples reaching operation frequencies above 10 GHz
while working at low external magnetic fields. Additionally, we perform broad
band ferromagnetic resonance measurements and cavity experiments that
demonstrate that the magnon-photon coupling strength can be estimated using
either open transmission lines or resonant cavities, yielding very good
agreement. Finally, we describe a simple theoretical framework based on
electromagnetic and micromagnetic simulations that successfully accounts for
the experimental results. This approach can be used to design hybrid quantum
systems exploiting whatsoever magnetostatic mode excited in ferromagnets of
arbitrary size and shape and to tune their operation conditions.",2207.03829v3
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
2022-09-01,Large spin-to-charge conversion at the two-dimensional interface of transition metal dichalcogenides and permalloy,"Spin-to-charge conversion is an essential requirement for the implementation
of spintronic devices. Recently, monolayers of semiconducting transition metal
dichalcogenides (TMDs) have attracted considerable interest for spin-to-charge
conversion due to their high spin-orbit coupling and lack of inversion symmetry
in their crystal structure. However, reports of direct measurement of
spin-to-charge conversion at TMD-based interfaces are very much limited. Here,
we report on the room temperature observation of a large spin-to-charge
conversion arising from the interface of Ni$_{80}$Fe$_{20}$ (Py) and four
distinct large area ($\sim 5\times2$~mm$^2$) monolayer (ML) TMDs namely,
MoS$_2$, MoSe$_2$, WS$_2$, and WSe$_2$. We show that both spin mixing
conductance and the Rashba efficiency parameter ($\lambda_{IREE}$) scales with
the spin-orbit coupling strength of the ML TMD layers. The $\lambda_{IREE}$
parameter is found to range between $-0.54$ and $-0.76$ nm for the four
monolayer TMDs, demonstrating a large spin-to-charge conversion. Our findings
reveal that TMD/ferromagnet interface can be used for efficient generation and
detection of spin current, opening new opportunities for novel spintronic
devices.",2209.00332v1
2022-09-08,Effects of the rf current and bias field direction on the transition from linear to non-linear gyrotropic dynamics in magnetic vortex structures,"We present a frequency-domain study of the dynamic behavior of a magnetic
vortex core within a single Permalloy disk by means of electrical detection and
micromagnetic simulations. When exciting the vortex core dynamics in a
non-linear regime, the lineshape of the rectified dc signal reveals a resonance
peak splitting which depends on the excitation amplitude. Using micromagnetic
simulations, we show that at high excitation power the peak splitting
originates from the nanosecond time scale quasi-periodic switching of the
vortex core polarity. Using lock-in detection, the rectified voltage is
integrated over a ms time scale, so that the net signal detected between the
two resonant peaks for a given range of parameters cancels out. The results are
in agreement with the reported effects of the in-plane static field magnitude
on the gyration dynamics, and complement them by detailed analysis of the
effects of the rf current amplitude and the azimuthal angle of the in-plane
bias magnetic field. Systematic characterization shows that a transition from
linear to nonlinear dynamical regime can be controlled by rf current as well as
by varying the magnitude and the direction of the bias magnetic field.",2209.03701v2
2022-09-27,Tailoring crosstalk between localized 1D spin-wave nanochannels using focused ion beams,"1D spin-wave conduits are envisioned as nanoscale components of
magnonics-based logic and computing schemes for future generation electronics.
`A-la-carte methods of versatile control of the local magnetization dynamics in
such nanochannels are highly desired for efficient steering of the spin waves
in magnonic devices. Here, we present a study of localized dynamical modes in
1-$\mu$m-wide Permalloy conduits probed by microresonator ferromagnetic
resonance technique. We clearly observe the lowest-energy edge mode in the
microstrip after its edges were finely trimmed by means of focused Ne$^+$ ion
irradiation. Furthermore, after milling the microstrip along its long axis by
focused ion beams, creating consecutively $\sim$50 and $\sim$100 nm gaps,
additional resonances emerge and are attributed to modes localized at the inner
edges of the separated strips. To visualize the mode distribution, spatially
resolved Brillouin light scattering microscopy was used showing an excellent
agreement with the ferromagnetic resonance data and confirming the mode
localization at the outer/inner edges of the strips depending on the magnitude
of the applied magnetic field. Micromagnetic simulations confirm that the
lowest-energy modes are localized within $\sim$15-nm-wide regions at the edges
of the strips and their frequencies can be tuned in a wide range (up to 5 GHz)
by changing the magnetostatic coupling (i.e. spatial separation) between the
microstrips.",2209.13180v2
2022-11-22,Generation of out-of-plane polarized spin current by spin swapping,"The generation of spin currents and their application to the manipulation of
magnetic states is fundamental to spintronics. Of particular interest are
chiral antiferromagnets that exhibit properties typical of ferromagnetic
materials even though they have negligible magnetization. Here, we report the
generation of a robust spin current with both in-plane and out-of-plane spin
polarization in epitaxial thin films of the chiral antiferromagnet Mn3Sn in
proximity to permalloy thin layers. By employing temperature-dependent
spin-torque ferromagnetic resonance, we find that the chiral antiferromagnetic
structure of Mn3Sn is responsible for an in-plane polarized spin current that
is generated from the interior of the Mn3Sn layer and whose temperature
dependence follows that of this layer's antiferromagnetic order. On the other
hand, the out-of-plane spin polarized spin current is unrelated to the chiral
antiferromagnetic structure and is instead the result of scattering from the
Mn3Sn/permalloy interface. We substantiate the later conclusion by performing
studies with several other non-magnetic metals all of which are found to
exhibit out-of-plane polarized spin currents arising from the spin swapping
effect.",2211.12398v1
2023-01-30,Investigation of Ultrafast Demagnetization and Gilbert Damping and their Correlation in Different Ferromagnetic Thin Films Grown Under Identical Conditions,"Following the demonstration of laser-induced ultrafast demagnetization in
ferromagnetic nickel, several theoretical and phenomenological propositions
have sought to uncover its underlying physics. In this work we revisit the
three temperature model (3TM) and the microscopic three temperature model
(M3TM) to perform a comparative analysis of ultrafast demagnetization in
20-nm-thick cobalt, nickel and permalloy thin films measured using an
all-optical pump-probe technique. In addition to the ultrafast dynamics at the
femtosecond timescales, the nanosecond magnetization precession and damping are
recorded at various pump excitation fluences revealing a fluence-dependent
enhancement in both the demagnetization times and the damping factors. We
confirm that the Curie temperature to magnetic moment ratio of a given system
acts as a figure of merit for the demagnetization time, while the
demagnetization times and damping factors show an apparent sensitivity to the
density of states at the Fermi level for a given system. Further, from
numerical simulations of the ultrafast demagnetization based on both the 3TM
and the M3TM, we extract the reservoir coupling parameters that best reproduce
the experimental data and estimate the value of the spin flip scattering
probability for each system. We discuss how the fluence-dependence of
inter-reservoir coupling parameters so extracted may reflect a role played by
nonthermal electrons in the magnetization dynamics at low laser fluences.",2301.12797v1
2023-03-12,Unusual magnetic hysteresis and transition between vortex to double pole states arising from interlayer coupling in diamond shaped nanostructures,"Controlling the magnetic ground states at the nanoscale is a long-standing
basic research problem and an important issue in magnetic storage technologies.
Here, we designed a nanostructured material that exhibits very unusual
hysteresis loops due to a transition between vortex and double pole states.
Arrays of 700 nm diamond-shape nanodots consisting of Py(30 nm)/Ru(tRu)/Py(30
nm) (Py, permalloy (Ni80Fe20)) trilayers were fabricated by interference
lithography and e-beam evaporation. We show that varying the Ru interlayer
spacer thickness (tRu) governs the interaction between the Py layers. We found
this interaction mainly mediated by two mechanisms: magnetostatic interaction
that favors antiparallel (antiferromagnetic, AFM) alignment of the Py layers
and exchange interaction that oscillates between ferromagnetic (FM) and AFM
couplings. For a certain range of Ru thicknesses, FM coupling dominates and
forms magnetic vortices in the upper and lower Py layers. For Ru thicknesses at
which AFM coupling dominates, the magnetic state in remanence is a double pole
structure. Our results showed that the interlayer exchange coupling interaction
remains finite even at 4 nm Ru thickness. The magnetic states in remanence,
observed by Magnetic Force Microscopy (MFM), are in good agreement with
corresponding hysteresis loops obtained by Magneto-Optic Kerr Effect (MOKE) and
micromagnetic simulations.",2303.06735v1
2023-03-20,Topological monopole's gauge field induced anomalous Hall effect in artificial honeycomb lattice,"Vortex magnetic structure in artificial honeycomb lattice provides a unique
platform to explore emergent properties due to the additional Berry phase
curvature imparted by chiral magnetization to circulating electrons via direct
interaction. We argue that while the perpendicularly-aligned magnetic component
leads to the quantized flux of monopole at the center of the Berry sphere, the
in-plane vortex circulation of magnetization gives rise to unexpected
non-trivial topological Berry phase due to the gauge field transformation. The
unprecedented effect signifies the importance of vector potential in
multiply-connected geometrical systems. Experimental confirmations to proposed
hypotheses are obtained from Hall resistance measurements on permalloy
honeycomb lattice. Investigation of the topological gauge transformation due to
the in-plane chirality reveals anomalous quasi-oscillatory behavior in Hall
resistance $R_{xy}$ as function of perpendicular field. The oscillatory nature
of $R_{xy}$ is owed to the fluctuation in equilibrium current as a function of
Fermi wave-vector $k_F$, envisaged under the proposed new formulation in this
article. Our synergistic approach suggests that artificially tunable
nanostructured material provides new vista to the exploration of topological
phenomena of strong fundamental importance.",2303.11506v1
2023-04-28,Persistent dynamic magnetic state in artificial honeycomb spin ice,"Topological magnetic charges, arising due to the non-vanishing magnetic flux
on spin ice vertices, serve as the origin of magnetic monopoles that traverse
the underlying lattice effortlessly. Unlike spin ice materials of atomic
origin, the dynamic state in artificial honeycomb spin ice is conventionally
described in terms of finite size domain wall kinetics that require magnetic
field or current application. Contrary to this common understanding, here we
show that thermally tunable artificial permalloy honeycomb lattice manifests a
perpetual dynamic state due to self-propelled magnetic charge defect relaxation
in the absence of any external tuning agent. Quantitative investigation of
magnetic charge defect dynamics using neutron spin echo spectroscopy reveals
sub-ns relaxation times that are comparable to monopole's relaxation in bulk
spin ices. Most importantly, the kinetic process remains unabated at low
temperature where thermal fluctuation is negligible. This suggests that dynamic
phenomena in honeycomb spin ice are mediated by quasi-particle type entities,
also confirmed by quantum Monte-Carlo simulations that replicate the kinetic
behavior. Our research unveils a new `macroscopic' magnetic particle that
shares many known traits of quantum particles, namely magnetic monopole and
magnon.",2305.00093v1
2023-08-23,Enhancing the Capture of Magnetic Nanoparticles Inside of Ferromagnetic Nanostructures Using External Magnetic Fields,"The influence of an external magnetic field upon the capture of 130 nm
magnetic nanoparticles (MNPs) by ferromagnetic nanostructures was investigated.
The magnetophoretic forces acting upon a nanoparticle were simulated in
external magnetic fields parallel and perpendicular to ferromagnetic
nanostructures consisting of arrays of antidots and dots. Changing the
direction of the external field was found to dramatically alter the
magnetophoretic forces acting on the particle and the trajectories of the MNPs.
A field parallel to the nanostructures' surfaces generated magnetophoretic
forces that directed the nanoparticle into the nanostructures. A perpendicular
field produced forces directing particles onto the structures' surfaces.
Nanostructures were etched into the surfaces of Permalloy films using ion beam
lithography. MNPs were then deposited onto the films' surfaces under a parallel
or perpendicular magnetic field. The distributions of particles in the
nanostructures were analysed to obtain the capture efficiencies of each
structure which indicate the proportion of particles trapped inside. Without an
external field, the highest efficiency was displayed by arrays of circular
antidots with circular dot arrays displaying the lowest. Antidot arrays
displayed higher capture efficiencies than dot arrays. Addition of a field
parallel to the surface significantly increased the capture efficiencies and
addition of a field perpendicular to the surface decreased the efficiencies.
Under the perpendicular field, the particles were instead caught on the outer
edges of the nanostructures. These results suggest that application of a
parallel external magnetic field promotes the capture of MNPs within
ferromagnetic nanostructures and a perpendicular field increases the capture of
MNPs onto the outer surface and edges of nanostructures.",2308.12321v1
2023-08-28,External magnetic fields enhance capture of magnetic nanoparticles flowing through molded microfluidic channels by ferromagnetic nanostructures,"Magnetic nanoparticles (MNPs) have many applications which require MNPs to be
captured and immobilized for their manipulation and sensing. For example, MNP
sensors based on detecting changes to the ferromagnetic resonances of an
antidot nanostructure exhibit better performance when the nanoparticles are
captured within the antidot inclusions. This study investigates the influence
of microfluidics upon the capture of MNPs by four geometries of antidot array
nanostructures hollowed into 30 nm-thick Permalloy films. The nanostructures
were exposed to a dispersion of 130 nm MNP clusters which passed through PDMS
microfluidic channels with a 400 {\mu}m circular cross-section fabricated from
wire molds. With the microfluidic flow of MNPs, the capture efficiency - the
ratio between the number of nanoparticles captured inside of the antidot
inclusions to the number outside the inclusions - decreased for all four
geometries compared to previous results introducing the particles via droplets
on the film surface. This indicates that most MNPs were passing over the
nanostructures, since there were no significant magnetophoretic forces acting
upon the particles. However, when a static magnetic field is applied, the
magnetophoretic forces generated by the nanostructure are stronger and the
capture efficiencies are significantly higher than those obtained using
droplets. In particular, circular antidots demonstrated the highest capture
efficiency among the four geometries of almost 83.1% when the magnetic field is
parallel to the film plane. In a magnetic field perpendicular to the film, the
circle antidots again show the highest capture efficiency of about 77%. These
results suggest that the proportion of nanoparticles captured inside antidot
inclusions is highest under a parallel magnetic field. Clearly, the geometry of
the nanostructure has a strong influence on the capture of MNPs.",2308.14543v1
2023-09-27,Correlation of Blocking and Néel Temperatures in Ultra-thin Metallic Antiferromagnets,"Nonvolatile spintronics-based devices that utilize electron spin both to
store and transport information face a great challenge when scaled to nano
dimensions due to loss of thermal stability and stray field induced disturbance
in closely packed magnetic bits. The potential replacement of ferromagnetic
materials with antiferromagnets may overcome some of these issues owing to the
superior robustness of sublattice spin orientations to magnetic field
disturbance as long as theyare kept well below the N\'eel temperature, which is
hard to measure with conventional methods, especially in the ultrathin limit.
In this work, we have employed spin pumping from a soft ferromagnetic NiFe
layer into widely used ultrathin metallic antiferromagnet Ir20Mn80, FeMn, PtMn,
PdMn or NiMn with thicknesses in the 0.7-3 nm range, as a probe to detect
damping enhancement during magnetic phase transitions. Independent measurements
of the blocking temperature with magnetometry reveal that temperature dependent
shifts in the resonance peaks can also be used to measure the blocking
temperature, allowing the analysis of the correlation between the N\'eel and
blocking temperatures in trilayers with permalloy and antiferromagnetic layer
separated by a 3 nm thick spacer layer. The thickness dependent
characterization of thermal stability in antiferromagnets provides a key
element for scalable and ultrafast antiferromagnetic spintronics.",2309.15545v1
2023-10-17,Size-dependence and high temperature stability of radial vortex magnetic textures imprinted by superconductor stray fields,"Swirling spin textures, including topologically non-trivial states, such as
skyrmions, chiral domain walls, and magnetic vortices, have garnered
significant attention within the scientific community due to their appeal from
both fundamental and applied points of view. However, their creation,
controlled manipulation, and stability are typically constrained to certain
systems with specific crystallographic symmetries, bulk, or interface
interactions, and/or a precise stacking sequence of materials. Here, we make
use of the stray field of YBa2Cu3O7-{\delta} superconducting microstructures in
ferromagnet/superconductor hybrids to imprint magnetic radial vortices in
permalloy at temperatures below the superconducting transition temperature
(TC), a method easily extended to other ferromagnets with in-plane magnetic
anisotropy. We examine the size dependence and temperature stability of the
imprinted magnetic configurations. We show that above TC, magnetic domains
retain memory of the imprinted spin texture. Micromagnetic modelling coupled
with a SC field model reveals that the stabilization mechanism leading to this
memory effect is mediated by microstructural defects. Superconducting control
of swirling spin textures below and above the superconducting transition
temperature holds promising prospects for shaping spintronics based on magnetic
textures.",2310.11298v1
2023-10-28,Einstein-de Haas torque as a discrete spectroscopic probe allows nanomechanical measurement of a magnetic resonance,"The Einstein-de Haas (EdH) effect is a fundamental, mechanical consequence of
any temporal change of magnetism in an object. EdH torque results from
conserving the object's total angular momentum: the angular momenta of all the
specimen's magnetic moments, together with its mechanical angular momentum.
Although the EdH effect is usually small and difficult to observe, it increases
in magnitude with detection frequency. We explore the frequency-dependence of
EdH torque for a thin film permalloy microstructure by employing a ladder of
flexural beam modes (with five distinct resonance frequencies spanning from 3
to 208 MHz) within a nanocavity optomechanical torque sensor via magnetic
hysteresis curves measured at mechanical resonances. At low DC fields the
gyrotropic resonance of a magnetic vortex spin texture overlaps the 208 MHz
mechanical mode. The massive EdH mechanical torques arising from this
co-resonance yield a fingerprint of vortex core pinning and depinning in the
sample. The experimental results are discussed in relation to mechanical
torques predicted from both macrospin (at high DC magnetic field) and
finite-difference solutions to the Landau-Lifshitz-Gilbert (LLG) equation. A
global fit of the LLG solutions to the frequency-dependent data reveals a
statistically significant discrepancy between the experimentally observed and
simulated torque phase behaviours at spin texture transitions that can be
reduced through the addition of a time constant to the conversion between
magnetic cross-product torque and mechanical torque, constrained by experiment
to be in the range of 0.5 - 4 ns.",2310.18546v2
2023-12-01,Nanocolumnar Material Platforms:Universal structural parameters revealed from optical anisotropy,"Nanostructures represent a frontier where meticulous attention to the control
and assessment of structural dimensions becomes a linchpin for their seamless
integration into diverse technological applications. By using integrative and
comprehensive methodical series of studies, we investigate the evolution of the
depolarization factors in the anisotropic Bruggeman effective medium
approximation, that are extremely sensitive to the changes in critical
dimensions of the nanostructure platforms. To this end, we fabricate spatially
coherent highly-ordered slanted nanocolumns from zirconia, silicon, titanium,
and permalloy on silicon substrates with varying column lengths using glancing
angle deposition. In tandem, broad-spectral range Mueller matrix spectroscopic
ellipsometry data, spanning from the near-infrared to the vacuum ultraviolet
(0.72 eV to 6.5 eV), is analyzed with a best-match model approach based on the
anisotropic Bruggeman effective medium theory. We thereby extracted the
anisotropic optical properties including complex dielectric function,
birefringence, and dichroism. Most notably, our research unveils a universal,
material-independent inverse relationship between depolarization factors and
column length. We envision that the presented universal relationship will
permit accurate prediction of optical properties of nanocolumnar thin films
improving their integration and optimization for optoelectronic and photonic
device applications.",2312.00779v1
2024-04-16,Reconfigurable spin-wave platform based on interplay between nanodots and waveguide in hybrid magnonic crystal,"We present a hybrid magnonic crystal composed of a chain of nanodots with
strong perpendicular magnetic anisotropy and Dzyaloshinskii-Moriya interaction,
positioned above a permalloy waveguide. The study examines two different
magnetization states in the nanodots: a single-domain state and an egg-shaped
skyrmion state. Due to the dipolar coupling between the dot and the waveguide,
a strongly bound hybrid magnetization texture is formed in the system. Our
numerical results show complex spin-wave spectra, combining the effects of
periodicity, magnetization texture, and hybridization of the propagating waves
in the waveguide with the dot/skyrmion modes. The systems are characterized by
different band gap sizes. For the skyrmion state, the azimuthal modes confined
to the skyrmion domain wall lead to the formation of flat bands at low
frequencies, while at higher frequencies we identify among them modes
interacting with the propagating waves, which can introduce additional
non-Bragg band gaps, as well as isolated modes leading to the formation of
bound states. On the other hand, the system with a single-domain state in
nanodots offers a wide range of frequencies where the spin waves are
predominantly in the waveguide. Thus, the study shows that the proposed hybrid
magnonic crystals have many distinct functionalities, highlighting their
reconfigurable potential, magnon-magnon couplings, mode localization, and bound
states overlapping with the propagating waves. This opens up potential
applications in analog and quantum magnonics, spin-wave filtering, and the
establishment of magnonic neural networks.",2404.10493v1
2002-07-26,Spin injection and spin accumulation in all-metal mesoscopic spin valves,"We study the electrical injection and detection of spin accumulation in
lateral ferromagnetic metal-nonmagnetic metal-ferromagnetic metal (F/N/F) spin
valve devices with transparent interfaces. Different ferromagnetic metals,
permalloy (Py), cobalt (Co) and nickel (Ni), are used as electrical spin
injectors and detectors. For the nonmagnetic metal both aluminium (Al) and
copper (Cu) are used. Our multi-terminal geometry allows us to experimentally
separate the spin valve effect from other magneto resistance signals such as
the anomalous magneto resistance (AMR) and Hall effects. We find that the AMR
contribution of the ferromagnetic contacts can dominate the amplitude of the
spin valve effect, making it impossible to observe the spin valve effect in a
'conventional' measurement geometry. In a 'non local' spin valve measurement we
are able to completely isolate the spin valve signal and observe clear spin
accumulation signals at T=4.2 K as well as at room temperature (RT). For
aluminum we obtain spin relaxation lengths (lambda_{sf}) of 1.2 mu m and 600 nm
at T=4.2 K and RT respectively, whereas for copper we obtain 1.0 mu m and 350
nm. The spin relaxation times tau_{sf} in Al and Cu are compared with theory
and results obtained from giant magneto resistance (GMR), conduction electron
spin resonance (CESR), anti-weak localization and superconducting tunneling
experiments. The spin valve signals generated by the Py electrodes (alpha_F
lambda_F=0.5 [1.2] nm at RT [T=4.2 K]) are larger than the Co electrodes
(alpha_F lambda_F=0.3 [0.7] nm at RT [T=4.2 K]), whereas for Ni (alpha_F
lambda_F<0.3 nm at RT and T=4.2 K) no spin signal is observed. These values are
compared to the results obtained from GMR experiments.",0207641v1
2014-02-05,Spin Transfer Torque Generated by the Topological Insulator Bi_2Se_3,"Magnetic devices are a leading contender for implementing memory and logic
technologies that are nonvolatile, that can scale to high density and high
speed, and that do not suffer wear-out. However, widespread applications of
magnetic memory and logic devices will require the development of efficient
mechanisms for reorienting their magnetization using the least possible current
and power. There has been considerable recent progress in this effort, in
particular discoveries that spin-orbit interactions in heavy metal/ferromagnet
bilayers can yield strong current-driven torques on the magnetic layer, via the
spin Hall effect in the heavy metal or the Rashba-Edelstein effect in the
ferromagnet. As part of the search for materials to provide even more efficient
spin-orbit-induced torques, some proposals have suggested topological
insulators (TIs), which possess a surface state in which the effects of
spin-orbit coupling are maximal in the sense that an electron's spin
orientation is locked relative to its propagation direction. Here we report
experiments showing that charge current flowing in-plane in a thin film of the
TI Bi_2Se_3 at room temperature can indeed apply a strong spin-transfer torque
to an adjacent ferromagnetic permalloy (Py = Ni81Fe19) thin film, with a
direction consistent with that expected from the topological surface state. We
find that the strength of the torque per unit charge current density in the
Bi_2Se_3 is greater than for any other spin-torque source material measured to
date, even for non-ideal TI films wherein the surface states coexist with bulk
conduction. Our data suggest that TIs have potential to enable very efficient
electrical manipulation of magnetic materials at room temperature for memory
and logic applications.",1402.1124v1
2014-08-13,Sub-nanosecond signal propagation in anisotropy engineered nanomagnetic logic chains,"Energy efficient nanomagnetic logic (NML) computing architectures propagate
and process binary information by relying on dipolar field coupling to reorient
closely-spaced nanoscale magnets. Signal propagation in nanomagnet chains of
various sizes, shapes, and magnetic orientations has been previously
characterized by static magnetic imaging experiments with low-speed adiabatic
operation; however the mechanisms which determine the final state and their
reproducibility over millions of cycles in high-speed operation (sub-ns time
scale) have yet to be experimentally investigated. Monitoring NML operation at
its ultimate intrinsic speed reveals features undetectable by conventional
static imaging including individual nanomagnetic switching events and
systematic error nucleation during signal propagation. Here, we present a new
study of NML operation in a high speed regime at fast repetition rates. We
perform direct imaging of digital signal propagation in permalloy nanomagnet
chains with varying degrees of shape-engineered biaxial anisotropy using
full-field magnetic soft x-ray transmission microscopy after applying single
nanosecond magnetic field pulses. Further, we use time-resolved magnetic
photo-emission electron microscopy to evaluate the sub-nanosecond dipolar
coupling signal propagation dynamics in optimized chains with 100 ps time
resolution as they are cycled with nanosecond field pulses at a rate of 3 MHz.
An intrinsic switching time of 100 ps per magnet is observed. These
experiments, and accompanying macro-spin and micromagnetic simulations, reveal
the underlying physics of NML architectures repetitively operated on nanosecond
timescales and identify relevant engineering parameters to optimize performance
and reliability.",1408.3157v1
2015-12-25,Collective magnetic response of inhomogeneous nanoisland FeNi films around the percolation transition,"By using superconducting quantum interference device (SQUID) magnetometry we
investigated anisotropic high-field (H < 7 T) low-temperature (10 K)
magnetization response of inhomogeneous nanoisland FeNi films grown by rf
sputtering deposition on Sitall (TiO2) glass substrates. In the grown FeNi
films, the FeNi layer nominal thickness varied from 0.6 to 2.5 nm, across the
percolation transition at the d_c=1.8 nm. We discovered that, beyond
conventional spin-magnetism of Fe21Ni79 permalloy, the extracted out-of-plane
magnetization response of the nanoisland FeNi films is not saturated in the
range of investigated magnetic fields and exhibits paramagnetic-like behavior.
We found that the anomalous out-of-plane magnetization response exhibits an
escalating slope with increase in the nominal film thickness from 0.6 to 1.1
nm, however, it decreases with further increase in the film thickness, and then
practically vanishes on approaching the FeNi film percolation threshold. At the
same time, the in-plane response demonstrates saturation behavior above 1.5-2
T, competing with anomalously large diamagnetic-like response, which becomes
pronounced at high magnetic fields. It is possible that the supported-metal
interaction leads to the creation of a thin charge-transfer (CT) layer and a
Schottky barrier at the FeNi film/Sitall (TiO2) interface. Then, in the system
with nanoscale circular domains, the observed anomalous paramagnetic-like
magnetization response can be associated with a large orbital moment of the
localized electrons. The observed magnetization response is determined by the
interplay between the paramagnetic- and diamagnetic-like contributions.",1512.07993v3
2018-11-05,Reply to Comment on Optical detection of transverse spin-Seebeck effect in permalloy film using Sagnac interferometer microscopy (arXiv:1810.13220),"In their Comment, Kimling and Kuschel (hereafter the commenters) challenge
our original interpretation of the magneto-optical Kerr effect (MOKE)
measurements using ultrasensitive Sagnac interferometer, claiming that the
transverse spin-Seebeck effect (TSSE) is not the only contribution to the
measured change in the Kerr rotation angle from a Ni80Fe20 (NiFe) ferromagnetic
(FM) slab subjected to a lateral temperature gradient in the presence of a
magnetic field. The authors assert that: (1) the TSSE, in general, has not been
completely proven so far, and that the existing theories, in particular the
phonon magnon drag model that we have used in our publication, in fact cannot
explain the original work of Uchida et al. (2) The commenters based their
critique on an estimate of the magnitude of the measured effect, arguing that
to observe the TSSE that we originally claimed, the temperature gradient in our
measurements should have been much larger than the value we measured. In this
Reply, firstly, we summarize previous literature reports on the TSSE response
in FM metallic systems. Secondly, we dispute the estimate of the necessary
large temperature gradient made by the commenters. Importantly, the Kerr effect
sensitivity to spin accumulation (via the TSSE response) has not been
recognized by the commenters, in fact it was mistakenly assumed that the Kerr
effect sensitivity to the spin accumulation by the TSSE is the same as the Kerr
sensitivity to the bulk magnetization change due to the temperature change. In
conclusion, we show that the TSSE is the only viable interpretation of our
original measurements, and that the phonon-magnon drag model is indeed capable
of explaining our results.",1811.01877v1
2014-06-01,Semi-Empirical Parameterization of Interatomic Interactions and Kinetics of the Atomic Ordering in Ni-Fe-C Permalloys and Elinvars,"Within the framework of the lattice-statics and static fluctuation-wave
methods, the available energies of strain-induced interaction of
interstitial-interstitial, interstitial-substitutional and
substitutional-substitutional impurity atomic pairs are collected and analysed
for f.c.c.-(Ni,Fe)-C solutions allowing for discrete atomic structure of the
host-crystal lattice. The lattice spacings, elasticity moduli and/or
quasi-elastic force parameters of the host-crystal lattice, and concentration
coefficients of the dilatation of solid-solution lattice due to the respective
solutes are selected as the input numerical experimental data used. The
above-mentioned interaction energies prove to have non-monotonically decreasing
and anisotropic dependences on discrete interatomic radius-vector, and
themselves are strong and long-range. In all f.c.c.-(Ni,Fe)-base solutions,
there is strain-induced attraction in many coordination shells. In general, the
strain-induced interaction between impurity atoms in gamma-Fe is weaker than in
alpha-Ni. The verification of applicability of the approximation of
strain-induced interaction of impurities for f.c.c.-(Ni,Fe)-C alloys showed
that it must be supplemented with additional short-range (electrochemical)
repulsion in the first coordination shell. Nevertheless, in any case, the
strain-induced interaction of impurity atoms must be taken into account for
analysis of structure and properties of f.c.c.-(Ni,Fe)-base solutions. The
Monte Carlo simulation procedures applied for constitution of a nanoscale
Fe-C-austenite crystallite and based on analysis of the dependences of numbers
of the different atomic configurations on C-C interatomic-interaction energies
reveal correlation between the potential energy of such a modeling system and
the numbers of iterations as well as Monte Carlo steps for the approach to
constrained equilibrium.",1406.0164v1
2021-02-17,Growth optimization of TaN for superconducting spintronics,"We have optimized the growth of superconducting TaN thin films on \ch{SiO2}
substrates via dc magnetron sputtering and extract a maximum superconducting
transition temperature of $T_{\mathrm{c}}=5$ K as well as a maximum critical
field $\mu_0H_{\mathrm{c2}}=(13.8\pm0.1)$ T. To investigate the impact of
spin-orbit interaction in superconductor/ferromagnet heterostructures, we then
analyze the magnetization dynamics of both normal state and superconducting
TaN/\ch{Ni80Fe20}(Permalloy, Py)-bilayers as a function of temperature using
broadband ferromagnetic resonance (bbFMR) spectroscopy. The phase sensitive
detection of the microwave transmission signal is used to quantitatively
extract the inverse current-induced torques of the bilayers. The results are
compared to our previous study on NbN/Py-bilayers. In the normal state of TaN,
we detect a positive damping-like current-induced torque $\sigma_{\mathrm{d}}$
from the inverse spin Hall effect (iSHE) and a small field-like torque
$\sigma_{\mathrm{f}}$ attributed to the inverse Rashba-Edelstein effect (iREE)
at the TaN/Py-interface. In the superconducting state of TaN, we detect a
negative $\sigma_{\mathrm{d}}$ attributed to the quasiparticle mediated inverse
spin Hall effect (QMiSHE) and the unexpected manifestation of a large positive
field-like $\sigma_{\mathrm{f}}$ of unknown origin matching our previous
results for NbN/Py-bilayers.",2102.09018v1
2021-03-24,Magnetism and Spin Dynamics in Room-Temperature van der Waals Magnet Fe$_5$GeTe$_2$,"Two-dimensional (2D) van der Waals (vdWs) materials have gathered a lot of
attention recently. However, the majority of these materials have Curie
temperatures that are well below room temperature, making it challenging to
incorporate them into device applications. In this work, we synthesized a
room-temperature vdW magnetic crystal Fe$_5$GeTe$_2$ with a Curie temperature
T$_c = 332$ K, and studied its magnetic properties by vibrating sample
magnetometry (VSM) and broadband ferromagnetic resonance (FMR) spectroscopy.
The experiments were performed with external magnetic fields applied along the
c-axis (H$\parallel$c) and the ab-plane (H$\parallel$ab), with temperatures
ranging from 300 K to 10 K. We have found a sizable Land\'e g-factor difference
between the H$\parallel$c and H$\parallel$ab cases. In both cases, the Land\'e
g-factor values deviated from g = 2. This indicates contribution of orbital
angular momentum to the magnetic moment. The FMR measurements reveal that
Fe$_5$GeTe$_2$ has a damping constant comparable to Permalloy. With reducing
temperature, the linewidth was broadened. Together with the VSM data, our
measurements indicate that Fe$_5$GeTe$_2$ transitions from ferromagnetic to
ferrimagnetic at lower temperatures. Our experiments highlight key information
regarding the magnetic state and spin scattering processes in Fe$_5$GeTe$_2$,
which promote the understanding of magnetism in Fe$_5$GeTe$_2$, leading to
implementations of Fe$_5$GeTe$_2$ based room-temperature spintronic devices.",2103.13433v2