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2004-10-30
|
Dynamics of Domain Wall in a Biaxial Ferromagnet With Spin-torque
|
The dynamics of the domain wall (DW) in a biaxial ferromagnet interacting
with a spin-polarized current are described by sine-gordon (SG) equation
coupled with Gilbert damping term in this paper. Within our frame-work of this
model, we obtain a threshold of the current in the motion of a single DW with
the perturbation theory on kink soliton solution to the corresponding
ferromagnetic system, and the threshold is shown to be dependent on the Gilbert
damping term. Also, the motion properties of the DW are discussed for the zero-
and nonzero-damping cases, which shows that our theory to describe the dynamics
of the DW are self-consistent.
|
0411005v3
|
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
|
2006-09-18
|
General Form of Magnetization Damping: Magnetization dynamics of a spin system evolving nonadiabatically and out of equilibrium
|
Using an effective Hamiltonian including the Zeeman and internal
interactions, we describe the quantum theory of magnetization dynamics when the
spin system evolves non-adiabatically and out of equilibrium. The
Lewis-Riesenfeld dynamical invariant method is employed along with the
Liouville-von Neumann equation for the density matrix. We derive a dynamical
equation for magnetization defined with respect to the density operator with a
general form of magnetization damping that involves the non-equilibrium
contribution in addition to the Landau-Lifshitz-Gilbert equation. Two special
cases of the radiation-spin interaction and the spin-spin exchange interaction
are considered. For the radiation-spin interaction, the damping term is shown
to be of the Gilbert type, while in the spin-spin exchange interaction case the
results depend on a coupled chain of correlation functions.
|
0609431v2
|
2010-12-25
|
Screw-pitch effect and velocity oscillation of domain-wall in ferromagnetic nanowire driven by spin-polarized current
|
We investigate the dynamics of domain wall in ferromagnetic nanowire with
spin-transfer torque. The critical current condition is obtained analytically.
Below the critical current, we get the static domain wall solution which shows
that the spin-polarized current can't drive domain wall moving continuously. In
this case, the spin-transfer torque plays both the anti-precession and
anti-damping roles, which counteracts not only the spin-precession driven by
the effective field but also Gilbert damping to the moment. Above the critical
value, the dynamics of domain wall exhibits the novel screw-pitch effect
characterized by the temporal oscillation of domain wall velocity and width,
respectively. Both the theoretical analysis and numerical simulation
demonstrate that this novel phenomenon arise from the conjunctive action of
Gilbert-damping and spin-transfer torque. We also find that the roles of
spin-transfer torque are entirely contrary for the cases of below and above the
critical current.
|
1012.5473v1
|
2014-06-24
|
Interface enhancement of Gilbert damping from first-principles
|
The enhancement of Gilbert damping observed for Ni80Fe20 (Py) films in
contact with the non-magnetic metals Cu, Pd, Ta and Pt, is quantitatively
reproduced using first-principles scattering theory. The "spin-pumping" theory
that qualitatively explains its dependence on the Py thickness is generalized
to include a number of factors known to be important for spin transport through
interfaces. Determining the parameters in this theory from first-principles
shows that interface spin-flipping makes an essential contribution to the
damping enhancement. Without it, a much shorter spin-flip diffusion length for
Pt would be needed than the value we calculate independently.
|
1406.6225v2
|
2015-09-06
|
Study of spin dynamics and damping on the magnetic nanowire arrays with various nanowire widths
|
We investigate the spin dynamics including Gilbert damping in the
ferromagnetic nanowire arrays. We have measured the ferromagnetic resonance of
ferromagnetic nanowire arrays using vector-network analyzer ferromagnetic
resonance (VNA-FMR) and analyzed the results with the micromagnetic
simulations. We find excellent agreement between the experimental VNA-FMR
spectra and micromagnetic simulations result for various applied magnetic
fields. We find that the demagnetization factor for longitudinal conditions, Nz
(Ny) increases (decreases) as decreasing the nanowire width in the
micromagnetic simulations. For the transverse magnetic field, Nz (Ny) increases
(decreases) as increasing the nanowire width. We also find that the Gilbert
damping constant increases from 0.018 to 0.051 as the increasing nanowire width
for the transverse case, while it is almost constant as 0.021 for the
longitudinal case.
|
1509.01807v1
|
2016-03-25
|
Large spin pumping effect in antisymmetric precession of Ni$_{79}$Fe$_{21}$/Ru/Ni$_{79}$Fe$_{21}$
|
In magnetic trilayer structures, a contribution to the Gilbert damping of
ferromagnetic resonance arises from spin currents pumped from one layer to
another. This contribution has been demonstrated for layers with weakly
coupled, separated resonances, where magnetization dynamics are excited
predominantly in one layer and the other layer acts as a spin sink. Here we
show that trilayer structures in which magnetizations are excited
simultaneously, antisymmetrically, show a spin-pumping effect roughly twice as
large. The antisymmetric (optical) mode of antiferromagnetically coupled
Ni$_{79}$Fe$_{21}$(8nm)/Ru/Ni$_{79}$Fe$_{21}$(8nm) trilayers shows a Gilbert
damping constant greater than that of the symmetric (acoustic) mode by an
amount as large as the intrinsic damping of Py ($\Delta
\alpha\simeq\textrm{0.006}$). The effect is shown equally in field-normal and
field-parallel to film plane geometries over 3-25 GHz. The results confirm a
prediction of the spin pumping model and have implications for the use of
synthetic antiferromagnets (SAF)-structures in GHz devices.
|
1603.07977v1
|
2016-07-18
|
Magnetic Skyrmion Transport in a Nanotrack With Spatially Varying Damping and Non-adiabatic Torque
|
Reliable transport of magnetic skyrmions is required for any future
skyrmion-based information processing devices. Here we present a micromagnetic
study of the in-plane current-driven motion of a skyrmion in a ferromagnetic
nanotrack with spatially sinusoidally varying Gilbert damping and/or
non-adiabatic spin-transfer torque coefficients. It is found that the skyrmion
moves in a sinusoidal pattern as a result of the spatially varying Gilbert
damping and/or non-adiabatic spin-transfer torque in the nanotrack, which could
prevent the destruction of the skyrmion caused by the skyrmion Hall effect. The
results provide a guide for designing and developing the skyrmion transport
channel in skyrmion-based spintronic applications.
|
1607.04983v3
|
2016-10-21
|
Spin transport and dynamics in all-oxide perovskite La$_{2/3}$Sr$_{1/3}$MnO$_3$/SrRuO$_3$ bilayers probed by ferromagnetic resonance
|
Thin films of perovskite oxides offer the possibility of combining emerging
concepts of strongly correlated electron phenomena and spin current in magnetic
devices. However, spin transport and magnetization dynamics in these complex
oxide materials are not well understood. Here, we experimentally quantify spin
transport parameters and magnetization damping in epitaxial perovskite
ferromagnet/paramagnet bilayers of La$_{2/3}$Sr$_{1/3}$MnO$_3$/SrRuO$_3$
(LSMO/SRO) by broadband ferromagnetic resonance spectroscopy. From the SRO
thickness dependence of Gilbert damping, we estimate a short spin diffusion
length of $\lesssim$1 nm in SRO and an interfacial spin-mixing conductance
comparable to other ferromagnet/paramagnetic-metal bilayers. Moreover, we find
that anisotropic non-Gilbert damping due to two-magnon scattering also
increases with the addition of SRO. Our results demonstrate LSMO/SRO as a
spin-source/spin-sink system that may be a foundation for examining
spin-current transport in various perovskite heterostructures.
|
1610.06661v1
|
2019-02-12
|
Ultra-low damping in lift-off structured yttrium iron garnet thin films
|
We show that using maskless photolithography and the lift-off technique,
patterned yttrium iron garnet thin films possessing ultra-low Gilbert damping
can be accomplished. The films of 70 nm thickness were grown on (001)-oriented
gadolinium gallium garnet by means of pulsed laser deposition, and they exhibit
high crystalline quality, low surface roughness, and the effective
magnetization of 127 emu/cm3. The Gilbert damping parameter is as low as
5x10-4. The obtained structures have well-defined sharp edges which along with
good structural and magnetic film properties pave a path in the fabrication of
high-quality magnonic circuits and oxide-based spintronic devices.
|
1902.04605v1
|
2019-02-20
|
CoFeB/MgO/CoFeB structures with orthogonal easy axes: perpendicular anisotropy and damping
|
We report on the Gilbert damping parameter $\alpha$, the effective
magnetization $4\pi M_{eff}$, and the asymmetry of the $g$-factor in
bottom-CoFeB(0.93~nm)/MgO(0.90--1.25~nm)/CoFeB(1.31~nm)-top as-deposited
systems.
Magnetization of CoFeB layers exhibits a specific noncollinear configuration
with orthogonal easy axes and with $4\pi M_{eff}$ values of $+2.2$ kG and
$-2.3$ kG for the bottom and top layers, respectively. We show that $4\pi
M_{eff}$ depends on the asymmetry $g_\perp - g_\parallel$ of the $g$-factor
measured in the perpendicular and the in-plane directions revealing a highly
nonlinear relationship. In contrast, the Gilbert damping is practically the
same for both layers. Annealing of the films results in collinear easy axes
perpendicular to the plane for both layers. However, the linewidth is strongly
increased due to enhanced inhomogeneous broadening.
|
1902.07563v1
|
2021-06-28
|
Stability of a Magnetically Levitated Nanomagnet in Vacuum: Effects of Gas and Magnetization Damping
|
In the absence of dissipation a non-rotating magnetic nanoparticle can be
stably levitated in a static magnetic field as a consequence of the spin origin
of its magnetization. Here we study the effects of dissipation on the stability
of the system, considering the interaction with the background gas and the
intrinsic Gilbert damping of magnetization dynamics. At large applied magnetic
fields we identify magnetization switching induced by Gilbert damping as the
key limiting factor for stable levitation. At low applied magnetic fields and
for small particle dimensions magnetization switching is prevented due to the
strong coupling of rotation and magnetization dynamics, and the stability is
mainly limited by the gas-induced dissipation. In the latter case, high vacuum
should be sufficient to extend stable levitation over experimentally relevant
timescales. Our results demonstrate the possibility to experimentally observe
the phenomenon of quantum spin stabilized magnetic levitation.
|
2106.14858v3
|
2021-10-31
|
Thermally induced all-optical ferromagnetic resonance in thin YIG films
|
All-optical ferromagnetic resonance (AO-FMR) is a powerful tool for local
detection of micromagnetic parameters, such as magnetic anisotropy, Gilbert
damping or spin stiffness. In this work we demonstrate that the AO-FMR method
can be used in thin films of Yttrium Iron Garnet (YIG) if a metallic capping
layer (Au, Pt) is deposited on top of the film. Magnetization precession is
triggered by heating of the metallic layer with femtosecond laser pulses. The
heating modifies the magneto-crystalline anisotropy of the YIG film and shifts
the quasi-equilibrium orientation of magnetization, which results in
precessional magnetization dynamics. The laser-induced magnetization precession
corresponds to a uniform (Kittel) magnon mode, with the precession frequency
determined by the magnetic anisotropy of the material as well as the external
magnetic field, and the damping time set by a Gilbert damping parameter. The
AO-FMR method thus enables measuring local magnetic properties, with spatial
resolution given only by the laser spot size.
|
2111.00586v1
|
2024-01-01
|
Calculation of Gilbert damping and magnetic moment of inertia using torque-torque correlation model within ab initio Wannier framework
|
Magnetization dynamics in magnetic materials are well described by the
modified semiclassical Landau-Lifshitz-Gilbert (LLG) equation, which includes
the magnetic damping $\alpha$ and the magnetic moment of inertia $\mathrm{I}$
tensors as key parameters. Both parameters are material-specific and physically
represent the time scales of damping of precession and nutation in
magnetization dynamics. $\alpha$ and $\mathrm{I}$ can be calculated quantum
mechanically within the framework of the torque-torque correlation model. The
quantities required for the calculation are torque matrix elements, the real
and imaginary parts of the Green's function and its derivatives. Here, we
calculate these parameters for the elemental magnets such as Fe, Co and Ni in
an ab initio framework using density functional theory and Wannier functions.
We also propose a method to calculate the torque matrix elements within the
Wannier framework. We demonstrate the effectiveness of the method by comparing
it with the experiments and the previous ab initio and empirical studies and
show its potential to improve our understanding of spin dynamics and to
facilitate the design of spintronic devices.
|
2401.00714v1
|
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
|
2008-05-22
|
Intrinsic and non-local Gilbert damping in polycrystalline nickel studied by Ti:Sapphire laser fs spectroscopy
|
The use of femtosecond laser pulses generated by a Ti:Sapphire laser system
allows us to gain an insight into the magnetization dynamics on time scales
from sub-picosecond up to 1 ns directly in the time domain. This experimental
technique is used to excite a polycrystalline nickel (Ni) film optically and
probe the dynamics afterwards. Different spin wave modes (the Kittel mode,
perpendicular standing spin-wave modes (PSSW) and dipolar spin-wave modes
(Damon-Eshbach modes)) are identified as the Ni thickness is increased. The
Kittel mode allows determination of the Gilbert damping parameter alpha
extracted from the magnetization relaxation time tau_alpha. The non-local
damping by spin currents emitted into a non-magnetic metallic layer of vanadium
(V), palladium (Pd) and the rare earth dysprosium (Dy) are studied for
wedge-shaped Ni films 1 nm-30 nm. The damping parameter increases from
alpha=0.045 intrinsic for nickel to alpha>0.10 for the heavy materials, such as
Pd and Dy, for the thinnest Ni films below 10 nm thickness. Also, for the
thinnest reference Ni film thickness, an increased magnetic damping below 4 nm
is observed. The origin of this increase is discussed within the framework of
line broadening by locally different precessional frequencies within the laser
spot region.
|
0805.3495v1
|
2015-06-18
|
The absence of intraband scattering in a consistent theory of Gilbert damping in metallic ferromagnets
|
Damping of magnetization dynamics in a ferromagnetic metal is usually
characterized by the Gilbert parameter alpha. Recent calculations of this
quantity, using a formula due to Kambersky, find that it is infinite for a
perfect crystal owing to an intraband scattering term which is of third order
in the spin-orbit parameter xi This surprising result conflicts with recent
work by Costa and Muniz who study damping numerically by direct calculation of
the dynamical transverse spin susceptibility in the presence of spin-orbit
coupling. We resolve this inconsistency by following the Costa-Muniz approach
for a slightly simplified model where it is possible to calculate alpha
analytically. We show that to second order in the spin-orbit parameter xi one
retrieves the Kambersky result for alpha, but to higher order one does not
obtain any divergent intraband terms. The present work goes beyond that of
Costa and Muniz by pointing out the necessity of including the effect of
long-range Coulomb interaction in calculating damping for large xi. A direct
derivation of the Kambersky formula is given which shows clearly the
restriction of its validity to second order in xi so that no intraband
scattering terms appear. This restriction has an important effect on the
damping over a substantial range of impurity content and temperature. The
experimental situation is discussed.
|
1506.05622v2
|
2020-02-07
|
Engineering Co$_2$MnAl$_x$Si$_{1-x}$ Heusler compounds as a model system to correlate spin polarization, intrinsic Gilbert damping and ultrafast demagnetization
|
Engineering of magnetic materials for developing better spintronic
applications relies on the control of two key parameters: the spin polarization
and the Gilbert damping responsible for the spin angular momentum dissipation.
Both of them are expected to affect the ultrafast magnetization dynamics
occurring on the femtosecond time scale. Here, we use engineered Co2MnAlxSi1-x
Heusler compounds to adjust the degree of spin polarization P from 60 to 100%
and investigate how it correlates with the damping. We demonstrate
experimentally that the damping decreases when increasing the spin polarization
from 1.1 10-3 for Co2MnAl with 63% spin polarization to an ultra-low value of
4.10-4 for the half-metal magnet Co2MnSi. This allows us investigating the
relation between these two parameters and the ultrafast demagnetization time
characterizing the loss of magnetization occurring after femtosecond laser
pulse excitation. The demagnetization time is observed to be inversely
proportional to 1-P and as a consequence to the magnetic damping, which can be
attributed to the similarity of the spin angular momentum dissipation processes
responsible for these two effects. Altogether, our high quality Heusler
compounds allow controlling the band structure and therefore the channel for
spin angular momentum dissipation.
|
2002.02686v1
|
2006-08-22
|
Simulation of stress-impedance effects in low magnetostrictive films
|
A theoretical study of stress-impedance effect based on the solution of
Landau-Lifsitz-Gilbert equation has been carried out. The results show that
stress impedance effects depend largely on several extrinsic (external bias
field, external frequency) and intrinsic (orientation and magnitude of uniaxial
anisotropy, damping) parameters.
|
0608488v1
|
2017-03-09
|
Material developments and domain wall based nanosecond-scale switching process in perpendicularly magnetized STT-MRAM cells
|
We investigate the Gilbert damping and the magnetization switching of
perpendicularly magnetized FeCoB-based free layers embedded in tunnel junctions
adequate for spin-torque operated memories. We study the influence of the boron
content in MgO / FeCoB /Ta systems alloys on their Gilbert damping after
crystallization annealing. Increasing the boron content from 20 to 30\%
increases the crystallization temperature, thereby postponing the onset of
elemental diffusion within the free layer. This reduction of the interdiffusion
of the Ta atoms helps maintaining the Gilbert damping at a low level of 0.009
without any penalty on the anisotropy and the magneto-transport properties up
to the 400$^\circ$C annealing required in CMOS back-end of line processing. In
addition, we show that dual MgO free layers of composition
MgO/FeCoB/Ta/FeCoB/MgO have a substantially lower damping than their
MgO/FeCoB/Ta counterparts, reaching damping parameters as low as 0.0039 for a 3
\r{A} thick Tantalum spacer. This confirms that the dominant channel of damping
is the presence of Ta impurities within the FeCoB alloy. On optimized tunnel
junctions, we then study the duration of the switching events induced by
spin-transfer-torque. We focus on the sub-threshold thermally activated
switching in optimal applied field conditions. From the electrical signatures
of the switching, we infer that once the nucleation has occurred, the reversal
proceeds by a domain wall sweeping though the device at a few 10 m/s. The
smaller the device, the faster its switching. We present an analytical model to
account for our findings. The domain wall velocity is predicted to scale
linearly with the current for devices much larger than the wall width. The wall
velocity depends on the Bloch domain wall width, such that the devices with the
lowest exchange stiffness will be the ones that host the domain walls with the
slowest mobilities.
|
1703.03198v3
|
2018-07-31
|
Comparative study of methodologies to compute the intrinsic Gilbert damping: interrelations, validity and physical consequences
|
Relaxation effects are of primary importance in the description of magnetic
excitations, leading to a myriad of methods addressing the phenomenological
damping parameters. In this work, we consider several well-established forms of
calculating the intrinsic Gilbert damping within a unified theoretical
framework, mapping out their connections and the approximations required to
derive each formula. This scheme enables a direct comparison of the different
methods on the same footing and a consistent evaluation of their range of
validity. Most methods lead to very similar results for the bulk ferromagnets
Fe, Co and Ni, due to the low spin-orbit interaction strength and the absence
of the spin pumping mechanism. The effects of inhomogeneities, temperature and
other sources of finite electronic lifetime are often accounted for by an
empirical broadening of the electronic energy levels. We show that the
contribution to the damping introduced by this broadening is additive, and so
can be extracted by comparing the results of the calculations performed with
and without spin-orbit interaction. Starting from simulated ferromagnetic
resonance spectra based on the underlying electronic structure, we
unambiguously demonstrate that the damping parameter obtained within the
constant broadening approximation diverges for three-dimensional bulk magnets
in the clean limit, while it remains finite for monolayers. Our work puts into
perspective the several methods available to describe and compute the Gilbert
damping, building a solid foundation for future investigations of magnetic
relaxation effects in any kind of material.
|
1807.11808v3
|
2002-07-30
|
Microscopic relaxation mechanisms and linear magnetization dynamics
|
Linear magnetization dynamics in the presense of a thermal bath is analyzed
for two general classes of microscopic damping mechanisms. The resulting
stochastic differential equations are always in the form of a damped harmonic
oscillator driven by a thermal field. The damping term contains both the
interaction mechanisms and the symmetry of the magnetic system. Back
transformation from the oscillator coordinates to the magnetization variables
results in a macroscopic tensor form of damping that reflects the system
anisotropy. Scalar Landau-Lifshitz-Gilbert damping term is valid only for
systems with axial symmetry. Analysis of FMR linewith measurements versus
frequency, temperature, and film thickness in NiFe films shows good agreement
with a combination of slow-relaxing impurity and magnon-electron confluence
processes.
|
0207721v1
|
2006-10-10
|
Spin-transfer in an open ferromagnetic layer: from negative damping to effective temperature
|
Spin-transfer is a typical spintronics effect that allows a ferromagnetic
layer to be switched by spin-injection. Most of the experimental results about
spin transfer are described on the basis of the Landau-Lifshitz-Gilbert
equation of the magnetization, in which additional current-dependent damping
factors are added, and can be positive or negative. The origin of the damping
can be investigated further by performing stochastic experiments, like one shot
relaxation experiments under spin-injection in the activation regime of the
magnetization. In this regime, the N\'eel-Brown activation law is observed
which leads to the introduction of a current-dependent effective temperature.
In order to justify the introduction of these counterintuitive parameters
(effective temperature and negative damping), a detailed thermokinetic analysis
of the different sub-systems involved is performed. We propose a thermokinetic
description of the different forms of energy exchanged between the electric and
the ferromagnetic sub-systems at a Normal/Ferromagnetic junction. The
corresponding Fokker Planck equations, including relaxations, are derived. The
damping coefficients are studied in terms of Onsager-Casimir transport
coefficients, with the help of the reciprocity relations. The effective
temperature is deduced in the activation regime.
|
0610264v1
|
2014-05-09
|
Magnetization dynamics and damping due to electron-phonon scattering in a ferrimagnetic exchange model
|
We present a microscopic calculation of magnetization damping for a magnetic
"toy model." The magnetic system consists of itinerant carriers coupled
antiferromagnetically to a dispersionless band of localized spins, and the
magnetization damping is due to coupling of the itinerant carriers to a phonon
bath in the presence of spin-orbit coupling. Using a mean-field approximation
for the kinetic exchange model and assuming the spin-orbit coupling to be of
the Rashba form, we derive Boltzmann scattering integrals for the distributions
and spin coherences in the case of an antiferromagnetic exchange splitting,
including a careful analysis of the connection between lifetime broadening and
the magnetic gap. For the Elliott-Yafet type itinerant spin dynamics we extract
dephasing and magnetization times T_1 and T_2 from initial conditions
corresponding to a tilt of the magnetization vector, and draw a comparison to
phenomenological equations such as the Landau-Lifshitz or the Gilbert damping.
We also analyze magnetization precession and damping for this system including
an anisotropy field and find a carrier mediated dephasing of the localized spin
via the mean-field coupling.
|
1405.2347v1
|
2015-11-13
|
Magnified Damping under Rashba Spin Orbit Coupling
|
The spin orbit coupling spin torque consists of the field-like [REF: S.G. Tan
et al., arXiv:0705.3502, (2007).] and the damping-like terms [REF: H.
Kurebayashi et al., Nature Nanotechnology 9, 211 (2014).] that have been widely
studied for applications in magnetic memory. We focus, in this article, not on
the spin orbit effect producing the above spin torques, but on its magnifying
the damping constant of all field like spin torques. As first order precession
leads to second order damping, the Rashba constant is naturally co-opted,
producing a magnified field-like damping effect. The Landau-Liftshitz-Gilbert
equations are written separately for the local magnetization and the itinerant
spin, allowing the progression of magnetization to be self-consistently locked
to the spin.
|
1511.04227v1
|
2022-05-13
|
Precession dynamics of a small magnet with non-Markovian damping: Theoretical proposal for an experiment to determine the correlation time
|
Recent advances in experimental techniques have made it possible to
manipulate and measure the magnetization dynamics on the femtosecond time scale
which is the same order as the correlation time of the bath degrees of freedom.
In the equations of motion of magnetization, the correlation of the bath is
represented by the non-Markovian damping. For development of the science and
technologies based on the ultrafast magnetization dynamics it is important to
understand how the magnetization dynamics depend on the correlation time. It is
also important to determine the correlation time experimentally. Here we study
the precession dynamics of a small magnet with the non-Markovian damping.
Extending the theoretical analysis of Miyazaki and Seki [J. Chem. Phys. 108,
7052 (1998)] we obtain analytical expressions of the precession angular
velocity and the effective damping constant for any values of the correlation
time under assumption of small Gilbert damping constant. We also propose a
possible experiment for determination of the correlation time.
|
2205.06399v1
|
2022-10-16
|
Magnetic damping anisotropy in the two-dimensional van der Waals material Fe$_3$GeTe$_2$ from first principles
|
Magnetization relaxation in the two-dimensional itinerant ferromagnetic van
der Waals material Fe$_3$GeTe$_2$, below the Curie temperature, is
fundamentally important for applications to low-dimensional spintronics
devices. We use first-principles scattering theory to calculate the
temperature-dependent Gilbert damping for bulk and single-layer Fe$_3$GeTe$_2$.
The calculated damping frequency of bulk Fe$_3$GeTe$_2$ increases monotonically
with temperature because of the dominance of resistivitylike behavior. By
contrast, a very weak temperature dependence is found for the damping frequency
of a single layer, which is attributed to strong surface scattering in this
highly confined geometry. A systematic study of the damping anisotropy reveals
that orientational anisotropy is present in both bulk and single-layer
Fe3GeTe2. Rotational anisotropy is significant at low temperatures for both the
bulk and a single layer and is gradually diminished by temperature-induced
disorder. The rotational anisotropy can be significantly enhanced by up to 430%
in gated single-layer Fe$_3$GeTe$_2$.
|
2210.08429v1
|
2016-09-26
|
Relativistic theory of spin relaxation mechanisms in the Landau-Lifshitz-Gilbert equation of spin dynamics
|
Starting from the Dirac-Kohn-Sham equation we derive the relativistic
equation of motion of spin angular momentum in a magnetic solid under an
external electromagnetic field. This equation of motion can be written in the
form of the well-known Landau-Lifshitz-Gilbert equation for a harmonic external
magnetic field, and leads to a more general magnetization dynamics equation for
a general time-dependent magnetic field. In both cases with an electronic
spin-relaxation term which stems from the spin-orbit interaction. We thus
rigorously derive, from fundamental principles, a general expression for the
anisotropic damping tensor which is shown to contain an isotropic Gilbert
contribution as well as an anisotropic Ising-like and a chiral,
Dzyaloshinskii-Moriya-like contribution. The expression for the spin relaxation
tensor comprises furthermore both electronic interband and intraband
transitions. We also show that when the externally applied electromagnetic
field possesses spin angular momentum, this will lead to an optical spin torque
exerted on the spin moment.
|
1609.07901v1
|
2002-11-22
|
Nonlinear microscopic relaxation of uniform magnetization precession
|
Dynamic relaxation for nonlinear magnetization excitation is analyzed. For
direct processes, such as magnon-electron scattering and two-magnon scattering,
the relaxation rate is determined from the linear case simply by utilizing the
magnetization oscillation frequency for nonlinear excitation. For an indirect
process, such as slow-relaxing impurities, the analysis gives an additional
relaxation term proportional to the excitation level. In all cases the
effective magnetization damping is increased compared to
Landau-Lifshitz-Gilbert damping.
|
0211499v1
|
2005-10-11
|
Non-damping magnetization oscillations in a single-domain ferromagnet
|
Non-damped oscillations of the magnetization vector of a ferromagnetic system
subject to a spin polarized current and an external magnetic field are studied
theoretically by solving the Landau-Lifshitz-Gilbert equation. It is shown that
the frequency and amplitude of such oscillations can be controlled by means of
an applied magnetic field and a spin current. The possibility of injection of
the oscillating spin current into a non-magnetic system is also discussed.
|
0510280v1
|
2007-03-27
|
Gauge Field Formulation of Adiabatic Spin Torques
|
Previous calculation of spin torques for small-amplitude magnetization
dynamics around a uniformly magnetized state [J. Phys. Soc. Jpn. {\bf 75}
(2006) 113706] is extended here to the case of finite-amplitude dynamics. This
is achieved by introducing an `` adiabatic'' spin frame for conduction
electrons, and the associated SU(2) gauge field. In particular, the Gilbert
damping is shown to arise from the time variation of the spin-relaxation source
terms in this new frame, giving a new physical picture of the damping. The
present method will allow a `` first-principle'' derivation of spin torques
without any assumptions such as rotational symmetry in spin space.
|
0703705v1
|
2008-05-09
|
Spin dynamics in (III,Mn)V ferromagnetic semiconductors: the role of correlations
|
We address the role of correlations between spin and charge degrees of
freedom on the dynamical properties of ferromagnetic systems governed by the
magnetic exchange interaction between itinerant and localized spins. For this
we introduce a general theory that treats quantum fluctuations beyond the
Random Phase Approximation based on a correlation expansion of the Green's
function equations of motion. We calculate the spin susceptibility, spin--wave
excitation spectrum, and magnetization precession damping. We find that
correlations strongly affect the magnitude and carrier concentration dependence
of the spin stiffness and magnetization Gilbert damping.
|
0805.1320v2
|
2010-01-16
|
Resonance Damping in Ferromagnets and Ferroelectrics
|
The phenomenological equations of motion for the relaxation of ordered phases
of magnetized and polarized crystal phases can be developed in close analogy
with one another. For the case of magnetized systems, the driving magnetic
field intensity toward relaxation was developed by Gilbert. For the case of
polarized systems, the driving electric field intensity toward relaxation was
developed by Khalatnikov. The transport times for relaxation into thermal
equilibrium can be attributed to viscous sound wave damping via
magnetostriction for the magnetic case and electrostriction for the
polarization case.
|
1001.2845v1
|
2016-05-15
|
Propagation of Thermally Induced Magnonic Spin Currents
|
The propagation of magnons in temperature gradients is investigated within
the framework of an atomistic spin model with the stochastic
Landau-Lifshitz-Gilbert equation as underlying equation of motion. We analyze
the magnon accumulation, the magnon temperature profile as well as the
propagation length of the excited magnons. The frequency distribution of the
generated magnons is investigated in order to derive an expression for the
influence of the anisotropy and the damping parameter on the magnon propagation
length. For soft ferromagnetic insulators with low damping a propagation length
in the range of some $\mu$m can be expected for exchange driven magnons.
|
1605.04543v1
|
2021-03-05
|
Universal spin wave damping in magnetic Weyl semimetals
|
We analyze the decay of spin waves into Stoner excitations in magnetic Weyl
semimetals. The lifetime of a mode is found to have a universal dependence on
its frequency and momentum, and on a few parameters that characterize the
relativistic Weyl spectrum. At the same time, Gilbert damping by Weyl electrons
is absent. The decay rate of spin waves is calculated perturbatively using the
s-d model of itinerant Weyl or Dirac electrons coupled to local moments. We
show that many details of the Weyl spectrum, such as the momentum-space
locations, dispersions and sizes of the Weyl Fermi pockets, can be deduced
indirectly by probing the spin waves of local moments using inelastic neutron
scattering.
|
2103.03885v1
|
2023-02-17
|
Control of magnon-photon coupling by spin torque
|
We demonstrate the influence of damping and field-like torques in the
magnon-photon coupling process by classically integrating the generalized
Landau-Lifshitz-Gilbert equation with RLC equation in which a phase correlation
between dynamic magnetization and microwave current through combined Amp\`ere
and Faraday effects are considered. We show that the gap between two hybridized
modes can be controlled in samples with damping parameter in the order of
$10^{-3}$ by changing the direction of the dc current density $J$ if a certain
threshold is reached. Our results suggest that an experimental realization of
the proposed magnon-photon coupling control mechanism is feasible in yttrium
iron garnet/Pt hybrid structures.
|
2302.08910v1
|
2017-03-21
|
Using rf voltage induced ferromagnetic resonance to study the spin-wave density of states and the Gilbert damping in perpendicularly magnetized disks
|
We study how the shape of the spinwave resonance lines in rf-voltage induced
FMR can be used to extract the spinwave density of states and the damping
within the precessing layer in nanoscale tunnel junctions that possess
perpendicular anisotropy. We work with a field applied along the easy axis to
preserve the uniaxial symmetry of the system. We describe the set-up to study
the susceptibility contributions of the spin waves in the field-frequency
space. We then identify the maximum device size above which the spinwaves can
no longer be studied in isolation as the linewidths of their responses make
them overlap. The rf-voltage induced signal is the sum of two voltages that
have comparable magnitudes: a first voltage that originates from the transverse
susceptibility and rectification by magnetoresistance and a second voltage that
arises from the non-linear longitudinal susceptibility and the resultant
time-averaged change of the micromagnetic configuration. The transverse and
longitudinal susceptibility signals have different dc bias dependences such
that they can be separated by measuring how the device rectifies the rf voltage
at different dc bias voltages. The transverse and longitudinal susceptibility
signals have different lineshapes; their joint studies can yield the Gilbert
damping of the free layer of the device with a degree of confidence that
compares well with standard FMR. Our method is illustrated on FeCoB-based free
layers in which the individual spin-waves can be sufficiently resolved only for
disk diameters below 200 nm. The resonance line shapes on devices with 90 nm
diameters are consistent with a Gilbert damping of 0.011. This damping of 0.011
exceeds the value of 0.008 measured on the unpatterned films, which indicates
that device-level measurements are needed for a correct evaluation of
dissipation.
|
1703.07310v2
|
2015-11-16
|
Determination of intrinsic damping of perpendicularly magnetized ultrathin films from time resolved precessional magnetization measurements
|
Magnetization dynamics are strongly influenced by damping. An effective
damping constant {\alpha}eff is often determined experimentally from the
spectral linewidth of the free induction decay of the magnetization after the
system is excited to its non-equilibrium state. Such an {\alpha}eff, however,
reflects both intrinsic damping as well as inhomogeneous broadening. In this
paper we compare measurements of the magnetization dynamics in ultrathin
non-epitaxial films having perpendicular magnetic anisotropy using two
different techniques, time-resolved magneto optical Kerr effect (TRMOKE) and
hybrid optical-electrical ferromagnetic resonance (OFMR). By using an external
magnetic field that is applied at very small angles to the film plane in the
TRMOKE studies, we develop an explicit closed-form analytical expression for
the TRMOKE spectral linewidth and show how this can be used to reliably extract
the intrinsic Gilbert damping constant. The damping constant determined in this
way is in excellent agreement with that determined from the OFMR method on the
same samples. Our studies indicate that the asymptotic high-field approach that
is often used in the TRMOKE method to distinguish the intrinsic damping from
the effective damping may result in significant error, because such high
external magnetic fields are required to make this approach valid that they are
out of reach. The error becomes larger the lower is the intrinsic damping
constant, and thus may account for the anomalously high damping constants that
are often reported in TRMOKE studies. In conventional ferromagnetic resonance
(FMR) studies, inhomogeneous contributions can be readily distinguished from
intrinsic damping contributions from the magnetic field dependence of the FMR
linewidth. Using the analogous approach, we show how reliable values of the
intrinsic damping can be extracted from TRMOKE.
|
1511.04802v1
|
2002-07-19
|
Gilbert Damping in Magnetic Multilayers
|
We study the enhancement of the ferromagnetic relaxation rate in thin films
due to the adjacent normal metal layers. Using linear response theory, we
derive the dissipative torque produced by the s-d exchange interaction at the
ferromagnet-normal metal interface. For a slow precession, the enhancement of
Gilbert damping constant is proportional to the square of the s-d exchange
constant times the zero-frequency limit of the frequency derivative of the
local dynamic spin susceptibility of the normal metal at the interface.
Electron-electron interactions increase the relaxation rate by the Stoner
factor squared. We attribute the large anisotropic enhancements of the
relaxation rate observed recently in multilayers containing palladium to this
mechanism. For free electrons, the present theory compares favorably with
recent spin-pumping result of Tserkovnyak et al. [Phys. Rev. Lett.
\textbf{88},117601 (2002)].
|
0207471v1
|
2002-08-06
|
Spin pumping and magnetization dynamics in metallic multilayers
|
We study the magnetization dynamics in thin ferromagnetic films and small
ferromagnetic particles in contact with paramagnetic conductors. A moving
magnetization vector causes \textquotedblleft pumping\textquotedblright of
spins into adjacent nonmagnetic layers. This spin transfer affects the
magnetization dynamics similar to the Landau-Lifshitz-Gilbert phenomenology.
The additional Gilbert damping is significant for small ferromagnets, when the
nonmagnetic layers efficiently relax the injected spins, but the effect is
reduced when a spin accumulation build-up in the normal metal opposes the spin
pumping. The damping enhancement is governed by (and, in turn, can be used to
measure) the mixing conductance or spin-torque parameter of the
ferromagnet--normal-metal interface. Our theoretical findings are confirmed by
agreement with recent experiments in a variety of multilayer systems.
|
0208091v2
|
2003-08-19
|
Magnetization relaxation in (Ga,Mn)As ferromagnetic semiconductors
|
We describe a theory of Mn local-moment magnetization relaxation due to p-d
kinetic-exchange coupling with the itinerant-spin subsystem in the
ferromagnetic semiconductor (Ga,Mn)As alloy. The theoretical Gilbert damping
coefficient implied by this mechanism is calculated as a function of Mn moment
density, hole concentration, and quasiparticle lifetime. Comparison with
experimental ferromagnetic resonance data suggests that in annealed strongly
metallic samples, p-d coupling contributes significantly to the damping rate of
the magnetization precession at low temperatures. By combining the theoretical
Gilbert coefficient with the values of the magnetic anisotropy energy, we
estimate that the typical critical current for spin-transfer magnetization
switching in all-semiconductor trilayer devices can be as low as $\sim 10^{5}
{\rm A cm}^{-2}$.
|
0308386v3
|
2005-12-29
|
Current-induced magnetization dynamics in disordered itinerant ferromagnets
|
Current-driven magnetization dynamics in ferromagnetic metals are studied in
a self-consistent adiabatic local-density approximation in the presence of
spin-conserving and spin-dephasing impurity scattering. Based on a quantum
kinetic equation, we derive Gilbert damping and spin-transfer torques entering
the Landau-Lifshitz equation to linear order in frequency and wave vector.
Gilbert damping and a current-driven dissipative torque scale identically and
compete, with the result that a steady current-driven domain-wall motion is
insensitive to spin dephasing in the limit of weak ferromagnetism. A uniform
magnetization is found to be much more stable against spin torques in the
itinerant than in the \textit{s}-\textit{d} model for ferromagnetism. A dynamic
spin-transfer torque reminiscent of the spin pumping in multilayers is
identified and shown to govern the current-induced domain-wall distortion.
|
0512715v4
|
2006-11-22
|
Magnetization damping in a local-density approximation
|
The linear response of itinerant transition metal ferromagnets to transverse
magnetic fields is studied in a self-consistent adiabatic local-density
approximation. The susceptibility is calculated from a microscopic Hamiltonian,
including spin-conserving impurities, impurity induced spin-orbit interaction
and magnetic impurities using the Keldysh formalism. The Gilbert damping
constant in the Landau-Lifshitz-Gilbert equation is identified, parametrized by
an effective transverse spin dephasing rate, and is found to be inversely
proportional to the exchange splitting. Our result justify the phenomenological
treatment of transverse spin dephasing in the study of current-induced
magnetization dynamics in weak, itinerant ferromagnets by Tserkovnyak
\textit{et al.}. We show that neglect of gradient corrections in the
quasiclassical transport equations leads to incorrect results when the exchange
potential becomes of the order of the Fermi energy.
|
0611588v1
|
2007-08-03
|
Strong spin-orbit induced Gilbert damping and g-shift in iron-platinum nanoparticles
|
The shape of ferromagnetic resonance spectra of highly dispersed, chemically
disordered Fe_{0.2}Pt_{0.8} nanospheres is perfectly described by the solution
of the Landau-Lifshitz-Gilbert (LLG) equation excluding effects by crystalline
anisotropy and superparamagnetic fluctuations. Upon decreasing temperature, the
LLG damping $\alpha(T)$ and a negative g-shift, g(T)-g_0, increase proportional
to the particle magnetic moments determined from the Langevin analysis of the
magnetization isotherms. These novel features are explained by the scattering
of the $q \to 0$ magnon from an electron-hole (e/h) pair mediated by the
spin-orbit coupling, while the sd-exchange can be ruled out. The large
saturation values, $\alpha(0)=0.76$ and $g(0)/g_0-1=-0.37$, indicate the
dominance of an overdamped 1 meV e/h-pair which seems to originate from the
discrete levels of the itinerant electrons in the d_p=3 nm nanoparticles.
|
0708.0463v1
|
2008-05-01
|
Chaotic Spin Dynamics of a Long Nanomagnet Driven by a Current
|
We study the spin dynamics of a long nanomagnet driven by an electrical
current. In the case of only DC current, the spin dynamics has a sophisticated
bifurcation diagram of attractors. One type of attractors is a weak chaos. On
the other hand, in the case of only AC current, the spin dynamics has a rather
simple bifurcation diagram of attractors. That is, for small Gilbert damping,
when the AC current is below a critical value, the attractor is a limit cycle;
above the critical value, the attractor is chaotic (turbulent). For normal
Gilbert damping, the attractor is always a limit cycle in the physically
interesting range of the AC current. We also developed a Melnikov integral
theory for a theoretical prediction on the occurrence of chaos. Our Melnikov
prediction seems performing quite well in the DC case. In the AC case, our
Melnikov prediction seems predicting transient chaos. The sustained chaotic
attractor seems to have extra support from parametric resonance leading to a
turbulent state.
|
0805.0147v1
|
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
|
2011-02-22
|
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
|
2012-07-28
|
Ultrafast optical control of magnetization in EuO thin films
|
All-optical pump-probe detection of magnetization precession has been
performed for ferromagnetic EuO thin films at 10 K. We demonstrate that the
circularly-polarized light can be used to control the magnetization precession
on an ultrafast time scale. This takes place within the 100 fs duration of a
single laser pulse, through combined contribution from two nonthermal
photomagnetic effects, i.e., enhancement of the magnetization and an inverse
Faraday effect. From the magnetic field dependences of the frequency and the
Gilbert damping parameter, the intrinsic Gilbert damping coefficient is
evaluated to be {\alpha} \approx 3\times10^-3.
|
1207.6686v1
|
2012-08-07
|
Observation of Coherent Helimagnons and Gilbert damping in an Itinerant Magnet
|
We study the magnetic excitations of itinerant helimagnets by applying
time-resolved optical spectroscopy to Fe0.8Co0.2Si. Optically excited
oscillations of the magnetization in the helical state are found to disperse to
lower frequency as the applied magnetic field is increased; the fingerprint of
collective modes unique to helimagnets, known as helimagnons. The use of
time-resolved spectroscopy allows us to address the fundamental magnetic
relaxation processes by directly measuring the Gilbert damping, revealing the
versatility of spin dynamics in chiral magnets. (*These authors contributed
equally to this work)
|
1208.1462v1
|
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
|
2013-01-10
|
First-principles calculation of the Gilbert damping parameter via the linear response formalism with application to magnetic transition-metals and alloys
|
A method for the calculations of the Gilbert damping parameter $\alpha$ is
presented, which based on the linear response formalism, has been implemented
within the fully relativistic Korringa-Kohn-Rostoker band structure method in
combination with the coherent potential approximation alloy theory. To account
for thermal displacements of atoms as a scattering mechanism, an alloy-analogy
model is introduced. This allows the determination of $\alpha$ for various
types of materials, such as elemental magnetic systems and ordered magnetic
compounds at finite temperature, as well as for disordered magnetic alloys at
$T = 0$ K and above. The effects of spin-orbit coupling, chemical and
temperature induced structural disorder are analyzed. Calculations have been
performed for the 3$d$ transition-metals bcc Fe, hcp Co, and fcc Ni, their
binary alloys bcc Fe$_{1-x}$Co$_{x}$, fcc Ni$_{1-x}$Fe$_x$, fcc
Ni$_{1-x}$Co$_x$ and bcc Fe$_{1-x}$V$_{x}$, and for 5d impurities in
transition-metal alloys. All results are in satisfying agreement with
experiment.
|
1301.2114v1
|
2013-08-01
|
Inverse Spin Hall Effect in nanometer-thick YIG/Pt system
|
High quality nanometer-thick (20 nm, 7 nm and 4 nm) epitaxial YIG films have
been grown on GGG substrates using pulsed laser deposition. The Gilbert damping
coefficient for the 20 nm thick films is 2.3 x 10-4 which is the lowest value
reported for sub-micrometric thick films. We demonstrate Inverse spin Hall
effect (ISHE) detection of propagating spin waves using Pt. The amplitude and
the lineshape of the ISHE voltage correlate well to the increase of the Gilbert
damping when decreasing thickness of YIG. Spin Hall effect based
loss-compensation experiments have been conducted but no change in the
magnetization dynamics could be detected.
|
1308.0192v1
|
2014-01-24
|
Wavenumber-dependent Gilbert damping in metallic ferromagnets
|
New terms to the dynamical equation of magnetization motion, associated with
spin transport, have been reported over the past several years. Each newly
identified term is thought to possess both a real and an imaginary effective
field leading to fieldlike and dampinglike torques on magnetization. Here we
show that three metallic ferromagnets possess an imaginary effective-field term
which mirrors the well-known real effective-field term associated with exchange
in spin waves. Using perpendicular standing spin wave resonance between 2-26
GHz, we evaluate the magnitude of the finite-wavenumber ($k$) dependent Gilbert
damping $\alpha$ in three typical device ferromagnets, Ni$_{79}$Fe$_{21}$, Co,
and Co$_{40}$Fe$_{40}$B$_{20}$, and demonstrate for the first time the presence
of a $k^2$ term as $\Delta\alpha=\Delta\alpha_0+A_{k}\cdot k^2$ in all three
metals. We interpret the new term as the continuum analog of spin pumping,
predicted recently, and show that its magnitude, $A_{k}$=0.07-0.1 nm$^2$, is
consistent with transverse spin relaxation lengths as measured by conventional
(interlayer) spin pumping.
|
1401.6467v2
|
2014-12-11
|
Deviation From the Landau-Lifshitz-Gilbert equation in the Inertial regime of the Magnetization
|
We investigate in details the inertial dynamics of a uniform magnetization in
the ferromagnetic resonance (FMR) context. Analytical predictions and numerical
simulations of the complete equations within the Inertial
Landau-Lifshitz-Gilbert (ILLG) model are presented. In addition to the usual
precession resonance, the inertial model gives a second resonance peak
associated to the nutation dynamics provided that the damping is not too large.
The analytical resolution of the equations of motion yields both the precession
and nutation angular frequencies. They are function of the inertial dynamics
characteristic time $\tau$, the dimensionless damping $\alpha$ and the static
magnetic field $H$. A scaling function with respect to $\alpha\tau\gamma H$ is
found for the nutation angular frequency, also valid for the precession angular
frequency when $\alpha\tau\gamma H\gg 1$. Beyond the direct measurement of the
nutation resonance peak, we show that the inertial dynamics of the
magnetization has measurable effects on both the width and the angular
frequency of the precession resonance peak when varying the applied static
field. These predictions could be used to experimentally identify the inertial
dynamics of the magnetization proposed in the ILLG model.
|
1412.3783v1
|
2015-01-02
|
Inertia, diffusion and dynamics of a driven skyrmion
|
Skyrmions recently discovered in chiral magnets are a promising candidate for
magnetic storage devices because of their topological stability, small size
($\sim 3-100$nm), and ultra-low threshold current density ($\sim
10^{6}$A/m$^2$) to drive their motion. However, the time-dependent dynamics has
hitherto been largely unexplored. Here we show, by combining the numerical
solution of the Landau-Lifshitz-Gilbert equation and the analysis of a
generalized Thiele's equation, that inertial effects are almost completely
absent in skyrmion dynamics driven by a time-dependent current. In contrast,
the response to time-dependent magnetic forces and thermal fluctuations depends
strongly on frequency and is described by a large effective mass and a (anti-)
damping depending on the acceleration of the skyrmion. Thermal diffusion is
strongly suppressed by the cyclotron motion and is proportional to the Gilbert
damping coefficient $\alpha$. This indicates that the skyrmion position is
stable, and its motion responds to the time-dependent current without delay or
retardation even if it is fast. These findings demonstrate the advantages of
skyrmions as information carriers.
|
1501.00444v1
|
2015-08-04
|
A Critical Analysis of the Feasibility of Pure Strain-Actuated Giant Magnetostrictive Nanoscale Memories
|
Concepts for memories based on the manipulation of giant magnetostrictive
nanomagnets by stress pulses have garnered recent attention due to their
potential for ultra-low energy operation in the high storage density limit.
Here we discuss the feasibility of making such memories in light of the fact
that the Gilbert damping of such materials is typically quite high. We report
the results of numerical simulations for several classes of toggle precessional
and non-toggle dissipative magnetoelastic switching modes. Material candidates
for each of the several classes are analyzed and forms for the anisotropy
energy density and ranges of material parameters appropriate for each material
class are employed. Our study indicates that the Gilbert damping as well as the
anisotropy and demagnetization energies are all crucial for determining the
feasibility of magnetoelastic toggle-mode precessional switching schemes. The
roles of thermal stability and thermal fluctuations for stress-pulse switching
of giant magnetostrictive nanomagnets are also discussed in detail and are
shown to be important in the viability, design, and footprint of
magnetostrictive switching schemes.
|
1508.00629v2
|
2015-12-16
|
Parity-time symmetry breaking in magnetic systems
|
The understanding of out-of-equilibrium physics, especially dynamic
instabilities and dynamic phase transitions, is one of the major challenges of
contemporary science, spanning the broadest wealth of research areas that range
from quantum optics to living organisms. Focusing on nonequilibrium dynamics of
an open dissipative spin system, we introduce a non-Hermitian Hamiltonian
approach, in which non-Hermiticity reflects dissipation and deviation from
equilibrium. The imaginary part of the proposed spin Hamiltonian describes the
effects of Gilbert damping and applied Slonczewski spin-transfer torque. In the
classical limit, our approach reproduces Landau-Lifshitz-Gilbert-Slonczewski
dynamics of a large macrospin. We reveal the spin-transfer torque-driven
parity-time symmetry-breaking phase transition corresponding to a transition
from precessional to exponentially damped spin dynamics. Micromagnetic
simulations for nanoscale ferromagnetic disks demonstrate the predicted effect.
Our findings can pave the way to a general quantitative description of
out-of-equilibrium phase transitions driven by spontaneous parity-time symmetry
breaking.
|
1512.05408v2
|
2017-01-11
|
The Cauchy problem for the Landau-Lifshitz-Gilbert equation in BMO and self-similar solutions
|
We prove a global well-posedness result for the Landau-Lifshitz equation with
Gilbert damping provided that the BMO semi-norm of the initial data is small.
As a consequence, we deduce the existence of self-similar solutions in any
dimension. In the one-dimensional case, we characterize the self-similar
solutions associated with an initial data given by some ($\mathbb{S}^2$-valued)
step function and establish their stability. We also show the existence of
multiple solutions if the damping is strong enough. Our arguments rely on the
study of a dissipative quasilinear Schr\"odinger obtained via the stereographic
projection and techniques introduced by Koch and Tataru.
|
1701.03083v2
|
2017-01-27
|
Structural scale $q-$derivative and the LLG-Equation in a scenario with fractionality
|
In the present contribution, we study the Landau-Lifshitz-Gilbert equation
with two versions of structural derivatives recently proposed: the scale
$q-$derivative in the non-extensive statistical mechanics and the axiomatic
metric derivative, which presents Mittag-Leffler functions as eigenfunctions.
The use of structural derivatives aims to take into account long-range forces,
possible non-manifest or hidden interactions and the dimensionality of space.
Having this purpose in mind, we build up an evolution operator and a deformed
version of the LLG equation. Damping in the oscillations naturally show up
without an explicit Gilbert damping term.
|
1701.08076v2
|
2018-10-17
|
Perpendicularly magnetized YIG films with small Gilbert damping constant and anomalous spin transport properties
|
The Y3Fe5O12 (YIG) films with perpendicular magnetic anisotropy (PMA) have
recently attracted a great deal of attention for spintronics applications.
Here, we report the induced PMA in the ultrathin YIG films grown on
(Gd2.6Ca0.4)(Ga4.1Mg0.25Zr0.65)O12 (SGGG) substrates by epitaxial strain
without preprocessing. Reciprocal space mapping shows that the films are
lattice-matched to the substrates without strain relaxation. Through
ferromagnetic resonance and polarized neutron reflectometry measurements, we
find that these YIG films have ultra-low Gilbert damping constant with a
magnetic dead layer as thin as about 0.3 nm at the YIG/SGGG interfaces.
Moreover, the transport behavior of the Pt/YIG/SGGG films reveals an
enhancement of spin mixing conductance and a large non-monotonic magnetic field
dependence of anomalous Hall effect as compared with the Pt/YIG/Gd3Ga5O12 (GGG)
films. The non-monotonic anomalous Hall signal is extracted in the temperature
range from 150 to 350 K, which has been ascribed to the possible non-collinear
magnetic order at the Pt/YIG interface induced by uniaxial strain.
|
1810.07384v2
|
2019-03-07
|
Current-induced motion of twisted skyrmions
|
Twisted skyrmions, whose helicity angles are different from that of Bloch
skyrmions and N\'eel skyrmions, have already been demonstrated in experiments
recently. In this work, we first contrast the magnetic structure and origin of
the twisted skyrmion with other three types of skyrmion including Bloch
skyrmion, N\'eel skyrmion and antiskyrmion. Following, we investigate the
dynamics of twisted skyrmions driven by the spin transfer toque (STT) and the
spin Hall effect (SHE) by using micromagnetic simulations. It is found that the
spin Hall angle of the twisted skyrmion is related to the dissipative force
tensor and the Gilbert damping both for the motions induced by the STT and the
SHE, especially for the SHE induced motion, the skyrmion Hall angle depends
substantially on the skyrmion helicity. At last, we demonstrate that the
trajectory of the twisted skyrmion can be controlled in a two dimensional plane
with a Gilbert damping gradient. Our results provide the understanding of
current-induced motion of twisted skyrmions, which may contribute to the
applications of skyrmion-based racetrack memories.
|
1903.02812v1
|
2019-07-03
|
Anisotropy of spin-transfer torques and Gilbert damping induced by Rashba coupling
|
Spin-transfer torques (STT), Gilbert damping (GD), and effective spin
renormalization (ESR) are investigated microscopically in a 2D Rashba
ferromagnet with spin-independent Gaussian white-noise disorder. Rashba
spin-orbit coupling induced anisotropy of these phenomena is thoroughly
analysed. For the case of two partly filled spin subbands, a remarkable
relation between the anisotropic STT, GD, and ESR is established. In the
absence of magnetic field and other torques on magnetization, this relation
corresponds to a current-induced motion of a magnetic texture with the
classical drift velocity of conduction electrons. Finally, we compute spin
susceptibility of the system and generalize the notion of spin-polarized
current.
|
1907.02041v3
|
2020-08-14
|
Large enhancement of spin pumping due to the surface bound states in normal metal/superconductor structures
|
We show that the spin pumping from ferromagnetic insulator into the adjacent
metallic spin sink can be strongly stimulated by the superconducting
correlations.
The key physical mechanism responsible for this effect is the presence of
quasiparticle surface states at the ferromagnetic insulator/superconductor
interface. We consider the minimal model when these states appear because of
the suppressed pairing constant within the interfacial normal layer. For thin
normal layers we obtain a strongly peaked temperature dependence of the Gilbert
damping coefficient which has been recently observed in such systems. For
thicker normal layers the Gilbert damping monotonically increases down to the
temperatures much smaller than the critical one. The suggested model paves the
way to controlling the temperature dependence of the spin pumping by
fabricating hybrid normal metal/superconductor spin sinks.
|
2008.06253v1
|
2021-11-05
|
Giant oscillatory Gilbert damping in superconductor/ferromagnet/superconductor junctions
|
Interfaces between materials with differently ordered phases present unique
opportunities for exotic physical properties, especially the interplay between
ferromagnetism and superconductivity in the ferromagnet/superconductor
heterostructures. The investigation of zero- and pi-junctions has been of
particular interest for both fundamental physical science and emerging
technologies. Here, we report the experimental observation of giant oscillatory
Gilbert damping in the superconducting Nb/NiFe/Nb junctions with respect to the
NiFe thickness. This observation suggests an unconventional spin pumping and
relaxation via zero-energy Andreev bound states that exist only in the
Nb/NiFe/Nb pi-junctions, but not in the Nb/NiFe/Nb zero-junctions. Our findings
could be important for further exploring the exotic physical properties of
ferromagnet/superconductor heterostructures, and potential applications of
ferromagnet pi-junctions in quantum computing, such as half-quantum flux
qubits.
|
2111.03233v1
|
2022-11-14
|
Magnetization Dynamics in Synthetic Antiferromagnets with Perpendicular Magnetic Anisotropy
|
Understanding the rich physics of magnetization dynamics in perpendicular
synthetic antiferromagnets (p-SAFs) is crucial for developing next-generation
spintronic devices. In this work, we systematically investigate the
magnetization dynamics in p-SAFs combining time-resolved magneto-optical Kerr
effect (TR-MOKE) measurements with theoretical modeling. These model analyses,
based on a Landau-Lifshitz-Gilbert approach incorporating exchange coupling,
provide details about the magnetization dynamic characteristics including the
amplitudes, directions, and phases of the precession of p-SAFs under varying
magnetic fields. These model-predicted characteristics are in excellent
quantitative agreement with TR-MOKE measurements on an asymmetric p-SAF. We
further reveal the damping mechanisms of two procession modes co-existing in
the p-SAF and successfully identify individual contributions from different
sources, including Gilbert damping of each ferromagnetic layer, spin pumping,
and inhomogeneous broadening. Such a comprehensive understanding of
magnetization dynamics in p-SAFs, obtained by integrating high-fidelity TR-MOKE
measurements and theoretical modeling, can guide the design of p-SAF-based
architectures for spintronic applications.
|
2211.07744v2
|
2023-05-17
|
Material Parameters for Faster Ballistic Switching of an In-plane Magnetized Nanomagnet
|
High-speed magnetization switching of a nanomagnet is necessary for faster
information processing. The ballistic switching by a pulsed magnetic filed is a
promising candidate for the high-speed switching. It is known that the
switching speed of the ballistic switching can be increased by increasing the
magnitude of the pulsed magnetic field. However it is difficult to generate a
strong and short magnetic field pulse in a small device. Here we explore
another direction to achieve the high-speed ballistic switching by designing
material parameters such as anisotropy constant, saturation magnetization, and
the Gilbert damping constant. We perform the macrospin simulations for the
ballistic switching of in-plane magnetized nano magnets with varying material
parameters. The results are analyzed based on the switching dynamics on the
energy density contour. We show that the pulse width required for the ballistic
switching can be reduced by increasing the magnetic anisotropy constant or by
decreasing the saturation magnetization. We also show that there exists an
optimal value of the Gilbert damping constant that minimizes the pulse width
required for the ballistic switching.
|
2305.10111v1
|
2023-05-23
|
Current-driven motion of magnetic topological defects in ferromagnetic superconductors
|
Recent years have seen a number of instances where magnetism and
superconductivity intrinsically coexist. Our focus is on the case where
spin-triplet superconductivity arises out of ferromagnetism, and we make a
hydrodynamic analysis of the effect of a charge supercurrent on magnetic
topological defects like domain walls and merons. We find that the emergent
electromagnetic field that arises out of the superconducting order parameter
provides a description for not only the physical quantities such as the local
energy flux density and the interaction between current and defects but also
the energy dissipation through magnetic dynamics of the Gilbert damping, which
becomes more prominent compared to the normal state as superconductivity
attenuates the energy dissipation through the charge sector. In particular, we
reveal that the current-induced dynamics of domain walls and merons in the
presence of the Gilbert damping give rise to the nonsingular $4\pi$ and $2\pi$
phase slips, respectively, revealing the intertwined dynamics of spin and
charge degrees of freedom in ferromagnetic superconductors.
|
2305.13564v1
|
2023-07-03
|
Magnetic lump motion in saturated ferromagnetic films
|
In this paper, we study in detail the nonlinear propagation of magnetic
soliton in a ferromagnetic film. The sample is magnetized to saturation by an
external field perpendicular to film plane. A new generalized (2+1)-dimensional
short-wave asymptotic model is derived. The bilinear-like forms of this
equation are constructed, and exact magnetic line soliton solutions are
exhibited. It is observed that a series of stable lumps can be generated by an
unstable magnetic soliton under Gaussian disturbance. Such magnetic lumps are
highly stable and can maintain their shapes and velocities during evolution or
collision. The interaction between lump and magnetic soliton, as well as
interaction between two lumps, are numerically investigated. We further discuss
the nonlinear motion of lumps in ferrites with Gilbert-damping and
inhomogeneous exchange effects. The results show that the Gilbert-damping
effects make the amplitude and velocity of the magnetic lump decay
exponentially during propagation. And the shock waves are generated from a lump
when quenching the strength of inhomogeneous exchange.
|
2307.00903v1
|
2005-03-24
|
Fast magnetization switching of Stoner particles: A nonlinear dynamics picture
|
The magnetization reversal of Stoner particles is investigated from the point
of view of nonlinear dynamics within the Landau-Lifshitz-Gilbert formulation.
The following results are obtained. 1) We clarify that the so-called
Stoner-Wohlfarth (SW) limit becomes exact when damping constant is infinitely
large. Under the limit, the magnetization moves along the steepest energy
descent path. The minimal switching field is the one at which there is only one
stable fixed point in the system. 2) For a given magnetic anisotropy, there is
a critical value for the damping constant, above which the minimal switching
field is the same as that of the SW-limit. 3) We illustrate how fixed points
and their basins change under a field along different directions. This change
explains well why a non-parallel field gives a smaller minimal switching field
and a short switching time. 4) The field of a ballistic magnetization reversal
should be along certain direction window in the presence of energy dissipation.
The width of the window depends on both of the damping constant and the
magnetic anisotropy. The upper and lower bounds of the direction window
increase with the damping constant. The window width oscillates with the
damping constant for a given magnetic anisotropy. It is zero for both zero and
infinite damping. Thus, the perpendicular field configuration widely employed
in the current experiments is not the best one since the damping constant in a
real system is far from zero.
|
0503594v1
|
2003-02-17
|
Magnetization dynamics with a spin-transfer torque
|
The magnetization reversal and dynamics of a spin valve pillar, whose lateral
size is 64$\times$64 nm$^2$, are studied by using micromagnetic simulation in
the presence of spin transfer torque. Spin torques display both characteristics
of magnetic damping (or anti-damping) and of an effective magnetic field. For a
steady-state current, both M-I and M-H hysteresis loops show unique features,
including multiple jumps, unusual plateaus and precessional states. These
states originate from the competition between the energy dissipation due to
Gilbert damping and the energy accumulation due to the spin torque supplied by
the spin current. The magnetic energy oscillates as a function of time even for
a steady-state current. For a pulsed current, the minimum width and amplitude
of the spin torque for achieving current-driven magnetization reversal are
quantitatively determined. The spin torque also shows very interesting thermal
activation that is fundamentally different from an ordinary damping effect.
|
0302337v1
|
2003-10-13
|
Domain wall mobility in nanowires: transverse versus vortex walls
|
The motion of domain walls in ferromagnetic, cylindrical nanowires is
investigated numerically by solving the Landau-Lifshitz-Gilbert equation for a
classical spin model in which energy contributions from exchange, crystalline
anisotropy, dipole-dipole interaction, and a driving magnetic field are
considered. Depending on the diameter, either transverse domain walls or vortex
walls are found. The transverse domain wall is observed for diameters smaller
than the exchange length of the given material. Here, the system behaves
effectively one-dimensional and the domain wall mobility agrees with a result
derived for a one-dimensional wall by Slonczewski. For low damping the domain
wall mobility decreases with decreasing damping constant. With increasing
diameter, a crossover to a vortex wall sets in which enhances the domain wall
mobility drastically. For a vortex wall the domain wall mobility is described
by the Walker-formula, with a domain wall width depending on the diameter of
the wire. The main difference is the dependence on damping: for a vortex wall
the domain wall mobility can be drastically increased for small values of the
damping constant up to a factor of $1/\alpha^2$.
|
0310277v1
|
2013-10-29
|
Observational Study of Large Amplitude Longitudinal Oscillations in a Solar Filament
|
On 20 August 2010 an energetic disturbance triggered damped large-amplitude
longitudinal (LAL) oscillations in almost an entire filament. In the present
work we analyze this periodic motion in the filament to characterize the
damping and restoring mechanism of the oscillation. Our method involves placing
slits along the axis of the filament at different angles with respect to the
spine of the filament, finding the angle at which the oscillation is clearest,
and fitting the resulting oscillation pattern to decaying sinusoidal and Bessel
functions. These functions represent the equations of motion of a pendulum
damped by mass accretion. With this method we determine the period and the
decaying time of the oscillation. Our preliminary results support the theory
presented by Luna and Karpen (2012) that the restoring force of LAL
oscillations is solar gravity in the tubes where the threads oscillate, and the
damping mechanism is the ongoing accumulation of mass onto the oscillating
threads. Following an earlier paper, we have determined the magnitude and
radius of curvature of the dipped magnetic flux tubes hosting a thread along
the filament, as well as the mass accretion rate of the filament threads, via
the fitted parameters.
|
1310.7657v1
|
2014-12-08
|
Magnetization Dynamics driven by Non-equilibrium Spin-Orbit Coupled Electron Gas
|
The dynamics of magnetization coupled to an electron gas via s-d exchange
interaction is investigated by using density matrix technique. Our theory shows
that non-equilibrium spin accumulation induces a spin torque and the electron
bath leads to a damping of the magnetization. For the two-dimensional
magnetization thin film coupled to the electron gas with Rashba spin-orbit
coupling, the result for the spin-orbit torques is consistent with the previous
semi-classical theory. Our theory predicts a damping of the magnetization,
which is absent in the semi-classical theory. The magnitude of the damping due
to the electron bath is comparable to the intrinsic Gilbert damping and may be
important in describing the magnetization dynamics of the system.
|
1412.2479v1
|
2016-04-11
|
All-Optical Study of Tunable Ultrafast Spin Dynamics in [Co/Pd]-NiFe Systems: The Role of Spin-Twist Structure on Gilbert Damping
|
We investigate optically induced ultrafast magnetization dynamics in [Co(0.5
nm)/Pd(1 nm)]x5/NiFe(t) exchange-spring samples with tilted perpendicular
magnetic anisotropy using a time-resolved magneto-optical Kerr effect
magnetometer. The competition between the out-of-plane anisotropy of the hard
layer, the in-plane anisotropy of the soft layer and the applied bias field
reorganizes the spins in the soft layer, which are modified further with the
variation in t. The spin-wave spectrum, the ultrafast demagnetization time, and
the extracted damping coefficient all depend on the spin distribution in the
soft layer, while the latter two also depend on the spin-orbit coupling between
the Co and Pd layers. The spin-wave spectra change from multimode to
single-mode as t increases. At the maximum field reached in this study, H=2.5
kOe, the damping shows a nonmonotonic dependence on t with a minimum at t=7.5
nm. For t<7.5 nm, intrinsic effects dominate, whereas for t>7.5 nm, extrinsic
effects govern the damping mechanisms.
|
1604.02998v1
|
2017-03-06
|
Damping dependence of spin-torque effects in thermally assisted magnetization reversal
|
Thermal fluctuations of nanomagnets driven by spin-polarized currents are
treated via the Landau-Lifshitz-Gilbert equation as generalized to include both
the random thermal noise field and Slonczewski spin-transfer torque terms. The
magnetization reversal time of such a nanomagnet is then evaluated for wide
ranges of damping by using a method which generalizes the solution of the
so-called Kramers turnover problem for mechanical Brownian particles, thereby
bridging the very low damping and intermediate damping Kramers escape rates, to
the analogous magnetic turnover problem. The reversal time is then evaluated
for a nanomagnet with the free energy density given in the standard form of
superimposed easy-plane and in-plane easy-axis anisotropies with the dc bias
field along the easy axis.
|
1703.01879v5
|
2017-05-09
|
Low spin wave damping in the insulating chiral magnet Cu$_{2}$OSeO$_{3}$
|
Chiral magnets with topologically nontrivial spin order such as Skyrmions
have generated enormous interest in both fundamental and applied sciences. We
report broadband microwave spectroscopy performed on the insulating chiral
ferrimagnet Cu$_{2}$OSeO$_{3}$. For the damping of magnetization dynamics we
find a remarkably small Gilbert damping parameter of about $1\times10^{-4}$ at
5 K. This value is only a factor of 4 larger than the one reported for the best
insulating ferrimagnet yttrium iron garnet. We detect a series of sharp
resonances and attribute them to confined spin waves in the mm-sized samples.
Considering the small damping, insulating chiral magnets turn out to be
promising candidates when exploring non-collinear spin structures for high
frequency applications.
|
1705.03416v1
|
2018-09-04
|
Separation of the two-magnon scattering contribution to damping for the determination of the spin mixing conductance
|
We present angle dependent measurements of the damping properties of
epitaxial Fe layers with MgO, Al and Pt capping layers. Based on the
preferential distribution of lattice defects following the crystal symmetry, we
make use of a model of the defect density to separate the contribution of
two-magnon scattering to the damping from the isotropic contribution
originating in the spin pumping effect, the viscous Gilbert damping and the
magnetic proximity effect. The separation of the two-magnon contribution, which
depends strongly on the defect density, allows for the measurement of a value
of the effective spin mixing conductance which is closer to the value
exclusively due to spin pumping. The influence of the defect density for
bilayers systems due to the different capping layers and to the unavoidable
spread in defect density from sample to sample is thus removed. This shows the
potential of studying spin pumping phenomena in fully ordered systems in which
this separation is possible, contrary to polycrystalline or amorphous metallic
thin films.
|
1809.01042v1
|
2006-02-09
|
Magnetization damping in polycrystalline Co ultra-thin films: Evidence for non-local effects
|
The magnetic properties and magnetization dynamics of polycrystalline
ultra-thin Co layers were investigated using a broadband ferromagnetic
resonance (FMR) technique at room temperature. A variable thickness (1 nm $\leq
t \leq$ 10 nm) Co layer is sandwiched between 10 nm thick Cu layers (10 nm Cu|
t Co|10 nm Cu), while materials in contact with the Cu outer interfaces are
varied to determine their influence on the magnetization damping. The resonance
field and the linewidth were studied for in-plane magnetic fields in field
swept experiments at a fixed frequency, from 4 to 25 GHz. The Co layers have a
lower magnetization density than the bulk, and an interface contribution to the
magnetic anisotropy normal to the film plane. The Gilbert damping, as
determined from the frequency dependence of the linewidth, increases with
decreasing Co layer thickness for films with outer Pt layers. This enhancement
is not observed in structures without Pt layers. The result can be understood
in terms of a non-local contribution to the damping due to spin pumping from Co
through the Cu layer and spin relaxation in Pt layers. Pt layers just 1.5 nm
thick are found to be sufficient to enhance the damping and thus act as
efficient "spin-sinks". In structures with Pt outer layers, this non-local
contribution to the damping becomes predominant when the Co layer is thinner
than 4 nm.
|
0602243v2
|
2020-04-09
|
Magnetic Damping in Epitaxial Fe Alloyed with Vanadium and Aluminum
|
To develop low-moment, low-damping metallic ferromagnets for power-efficient
spintronic devices, it is crucial to understand how magnetic relaxation is
impacted by the addition of nonmagnetic elements. Here, we compare magnetic
relaxation in epitaxial Fe films alloyed with light nonmagnetic elements of V
and Al. FeV alloys exhibit lower intrinsic damping compared to pure Fe, reduced
by nearly a factor of 2, whereas damping in FeAl alloys increases with Al
content. Our experimental and computational results indicate that reducing the
density of states at the Fermi level, rather than the average atomic number,
has a more significant impact in lowering damping in Fe alloyed with light
elements. Moreover, FeV is confirmed to exhibit an intrinsic Gilbert damping
parameter of $\simeq$0.001, among the lowest ever reported for ferromagnetic
metals.
|
2004.04840v3
|
2014-05-19
|
Comparison of micromagnetic parameters of ferromagnetic semiconductors (Ga,Mn)(As,P) and (Ga,Mn)As
|
We report on the determination of micromagnetic parameters of epilayers of
the ferromagnetic semiconductor (Ga,Mn)As, which has easy axis in the sample
plane, and (Ga,Mn)(As,P) which has easy axis perpendicular to the sample plane.
We use an optical analog of ferromagnetic resonance where the
laser-pulse-induced precession of magnetization is measured directly in the
time domain. By the analysis of a single set of pump-and-probe magneto-optical
data we determined the magnetic anisotropy fields, the spin stiffness and the
Gilbert damping constant in these two materials. We show that incorporation of
10% of phosphorus in (Ga,Mn)As with 6% of manganese leads not only to the
expected sign change of the perpendicular to plane anisotropy field but also to
an increase of the Gilbert damping and to a reduction of the spin stiffness.
The observed changes in the micromagnetic parameters upon incorporating P in
(Ga,Mn)As are consistent with the reduced hole density, conductivity, and Curie
temperature of the (Ga,Mn)(As,P) material. We report that the magnetization
precession damping is stronger for the n = 1 spin wave resonance mode than for
the n = 0 uniform magnetization precession mode.
|
1405.4677v1
|
2015-03-24
|
Spin dynamics and frequency dependence of magnetic damping study in soft ferromagnetic FeTaC film with a stripe domain structure
|
Perpendicular magnetic anisotropy (PMA) and low magnetic damping are the key
factors for the free layer magnetization switching by spin transfer torque
technique in magnetic tunnel junction devices. The magnetization precessional
dynamics in soft ferromagnetic FeTaC thin film with a stripe domain structure
was explored in broad band frequency range by employing micro-strip
ferromagnetic resonance technique. The polar angular variation of resonance
field and linewidth at different frequencies have been analyzed numerically
using Landau-Lifshitz-Gilbert equation by taking into account the total free
energy density of the film. The numerically estimated parameters Land\'{e}
$g$-factor, PMA constant, and effective magnetization are found to be 2.1,
2$\times10^{5}$ erg/cm$^{3}$ and 7145 Oe, respectively. The frequency
dependence of Gilbert damping parameter ($\alpha$) is evaluated by considering
both intrinsic and extrinsic effects into the total linewidth analysis. The
value of $\alpha$ is found to be 0.006 at 10 GHz and it increases with
decreasing precessional frequency.
|
1503.07043v5
|
2016-05-22
|
Low Gilbert damping in Co2FeSi and Fe2CoSi films
|
Thin highly textured Fe$_{\mathrm{1+x}}$Co$_{\mathrm{2-x}}$Si ($0 \leq$ x
$\leq 1$) films were prepared on MgO (001) substrates by magnetron
co-sputtering. The magneto-optic Kerr effect (MOKE) and ferromagnetic resonance
(FMR) measurements were used to investigate the composition dependence of the
magnetization, the magnetic anisotropy, the gyromagnetic ratio and the
relaxation of the films. The effective magnetization for the thin
Fe$_{\mathrm{1+x}}$Co$_{\mathrm{2-x}}$Si films, determined by FMR measurements,
are consistent with the Slater Pauling prediction. Both MOKE and FMR
measurements reveal a pronounced fourfold anisotropy distribution for all
films. In addition we found a strong influence of the stoichiometry on the
anisotropy as the cubic anisotropy strongly increases with increasing Fe
concentration. The gyromagnetic ratio is only weakly dependent on the
composition. We find low Gilbert damping parameters for all films with values
down to $0.0012\pm0.00012$ for Fe$_{1.75}$Co$_{1.25}$Si. The effective damping
parameter for Co$_2$FeSi is found to be $0.0018\pm 0.0004$. We also find a
pronounced anisotropic relaxation, which indicates significant contributions of
two-magnon scattering processes that is strongest along the easy axes of the
films. This makes thin Fe$_{\mathrm{1+x}}$Co$_{\mathrm{2-x}}$Si films ideal
materials for the application in STT-MRAM devices.
|
1605.06797v1
|
2017-09-21
|
Low Gilbert Damping Constant in Perpendicularly Magnetized W/CoFeB/MgO Films with High Thermal Stability
|
Perpendicular magnetic materials with low damping constant and high thermal
stability have great potential for realizing high-density, non-volatile, and
low-power consumption spintronic devices, which can sustain operation
reliability for high processing temperatures. In this work, we study the
Gilbert damping constant ({\alpha}) of perpendicularly magnetized W/CoFeB/MgO
films with a high perpendicular magnetic anisotropy (PMA) and superb thermal
stability. The {\alpha} of these PMA films annealed at different temperatures
is determined via an all-optical Time-Resolved Magneto-Optical Kerr Effect
method. We find that {\alpha} of these W/CoFeB/MgO PMA films decreases with
increasing annealing temperature, reaches a minimum of {\alpha} = 0.016 at an
annealing temperature of 350 {\deg}C, and then increases to 0.024 after
post-annealing at 400 {\deg}C. The minimum {\alpha} observed at 350 {\deg}C is
rationalized by two competing effects as the annealing temperature becomes
higher: the enhanced crystallization of CoFeB and dead-layer growth occurring
at the two interfaces of the CoFeB layer. We further demonstrate that {\alpha}
of the 400 {\deg}C-annealed W/CoFeB/MgO film is comparable to that of a
reference Ta/CoFeB/MgO PMA film annealed at 300 {\deg}C, justifying the
enhanced thermal stability of the W-seeded CoFeB films.
|
1709.07483v1
|
2022-02-06
|
Enhancing Perpendicular Magnetic Anisotropy in Garnet Ferrimagnet by Interfacing with Few-Layer WTe2
|
Engineering magnetic anisotropy in a ferro- or ferrimagnetic (FM) thin film
is crucial in spintronic device. One way to modify the magnetic anisotropy is
through the surface of the FM thin film. Here, we report the emergence of a
perpendicular magnetic anisotropy (PMA) induced by interfacial interactions in
a heterostructure comprised of a garnet ferrimagnet, Y3Fe5O12 (YIG), and the
low-symmetry, high spin orbit coupling (SOC) transition metal dichalcogenide,
WTe2. At the same time, we also observed an enhancement in Gilbert damping in
the WTe2 covered YIG area. Both the magnitude of interface-induced PMA and the
Gilbert damping enhancement have no observable WTe2 thickness dependence down
to single quadruple-layer, indicating that the interfacial interaction plays a
critical role. The ability of WTe2 to enhance the PMA in FM thin film, combined
with its previously reported capability to generate out-of-plane damping like
spin torque, makes it desirable for magnetic memory applications.
|
2202.02834v1
|
2018-10-25
|
Time-retarded damping and magnetic inertia in the Landau-Lifshitz-Gilbert equation self-consistently coupled to electronic time-dependent nonequilibrium Green functions
|
The conventional Landau-Lifshitz-Gilbert (LLG) equation is a widely used tool
to describe dynamics of local magnetic moments, viewed as classical vectors of
fixed length, with their change assumed to take place simultaneously with the
cause. Here we demonstrate that recently developed [M. D. Petrovi\'{c} {\em et
al.}, {\tt arXiv:1802.05682}] self-consistent coupling of the LLG equation to
time-dependent quantum-mechanical description of electrons microscopically
generates time-retarded damping in the LLG equation described by a memory
kernel which is also spatially dependent. For sufficiently slow dynamics of
local magnetic moments, the memory kernel can be expanded to extract the
Gilbert damping (proportional to first time derivative of magnetization) and
magnetic inertia (proportional to second time derivative of magnetization)
terms whose parameters, however, are time-dependent in contrast to
time-independent parameters used in the conventional LLG equation. We use
examples of single or multiple magnetic moments precessing in an external
magnetic field, as well as field-driven motion of a magnetic domain wall (DW),
to quantify the difference in their time evolution computed from conventional
LLG equation vs. TDNEGF+LLG quantum-classical hybrid approach. The faster DW
motion predicted by TDNEGF+LLG approach reveals that important quantum effects,
stemming from finite amount of time which it takes for conduction electron spin
to react to the motion of classical local magnetic moments, are missing from
conventional classical micromagnetics simulations. We also demonstrate large
discrepancy between TDNEGF+LLG-computed numerically exact and, therefore,
nonperturbative result for charge current pumped by a moving DW and the same
quantity computed by perturbative spin motive force formula combined with the
conventional LLG equation.
|
1810.11016v2
|
2019-08-08
|
Annihilation of topological solitons in magnetism with spin wave burst finale: The role of nonequilibrium electrons causing nonlocal damping and spin pumping over ultrabroadband frequency range
|
We not only reproduce burst of short-wavelength spin waves (SWs) observed in
recent experiment [S. Woo et al., Nat. Phys. 13, 448 (2017)] on
magnetic-field-driven annihilation of two magnetic domain walls (DWs) but,
furthermore, we predict that this setup additionally generates highly unusual}
pumping of electronic spin currents in the absence of any bias voltage. Prior
to the instant of annihilation, their power spectrum is ultrabroadband, so they
can be converted into rapidly changing in time charge currents, via the inverse
spin Hall effect, as a source of THz radiation of bandwidth $\simeq 27$ THz
where the lowest frequency is controlled by the applied magnetic field. The
spin pumping stems from time-dependent fields introduced into the quantum
Hamiltonian of electrons by the classical dynamics of localized magnetic
moments (LMMs) comprising the domains. The pumped currents carry spin-polarized
electrons which, in turn, exert backaction on LMMs in the form of nonlocal
damping which is more than twice as large as conventional local Gilbert
damping. The nonlocal damping can substantially modify the spectrum of emitted
SWs when compared to widely-used micromagnetic simulations where conduction
electrons are completely absent. Since we use fully microscopic (i.e.,
Hamiltonian-based) framework, self-consistently combining time-dependent
electronic nonequilibrium Green functions with the Landau-Lifshitz-Gilbert
equation, we also demonstrate that previously derived phenomenological formulas
miss ultrabroadband spin pumping while underestimating the magnitude of
nonlocal damping due to nonequilibrium electrons.
|
1908.03194v5
|
2006-06-05
|
Phenomenological theory of current driven exchange switching in ferromagnetic nanojunctions
|
Phenomenological approach is developed in the theory of spin-valve type
ferromagnetic junctions to describe exchange switching by current flowing
perpendicular to interfaces. Forward and backward current switching effects are
described and they may be principally different in nature. Mobile electron
spins are considered as being free in all the contacting ferromagnetic layers.
Joint action of the following two current effects is investigated: the
nonequilibrium longitudinal spin-injection effective field and the transverse
spin-transfer surface torque. Dispersion relation for fluctuations is derived
and solved for a junction model having spatially localized spin transfer
torque: depth of the torque penetration into the free layer is assumed much
smaller than the total free layer thickness. Some critical value of the well
known Gilbert damping constant is established for the first time. Spin transfer
torque dominates in the instability threshold determination for small enough
damping constants, while the spin-injection effective field dominates for high
damping. Fine interplay between spin transfer torque and spin injection is
necessary to provide a hysteretic behavior of the resistance versus current
dependence. The state diagram building up shows the possibility of
non-stationary (time dependent) nonlinear states arising due to instability
development. Calculations lead to the instability rise time values of the order
of 0.1 ns. Spin wave resonance frequency spectrum softening occurs under the
current growing to the instability threshold. Magnetization fluctuations above
the threshold rise oscillating with time for low damping, but rise
aperiodically and much more rapid for high damping.
|
0606102v2
|
2015-07-29
|
Spin dynamics and relaxation in the classical-spin Kondo-impurity model beyond the Landau-Lifschitz-Gilbert equation
|
The real-time dynamics of a classical spin in an external magnetic field and
locally exchange coupled to an extended one-dimensional system of
non-interacting conduction electrons is studied numerically. Retardation
effects in the coupled electron-spin dynamics are shown to be the source for
the relaxation of the spin in the magnetic field. Total energy and spin is
conserved in the non-adiabatic process. Approaching the new local ground state
is therefore accompanied by the emission of dispersive wave packets of
excitations carrying energy and spin and propagating through the lattice with
Fermi velocity. While the spin dynamics in the regime of strong exchange
coupling J is rather complex and governed by an emergent new time scale, the
motion of the spin for weak J is regular and qualitatively well described by
the Landau-Lifschitz-Gilbert (LLG) equation. Quantitatively, however, the full
quantum-classical hybrid dynamics differs from the LLG approach. This is
understood as a breakdown of weak-coupling perturbation theory in J in the
course of time. Furthermore, it is shown that the concept of the Gilbert
damping parameter is ill-defined for the case of a one-dimensional system.
|
1507.08227v2
|
2008-09-26
|
Damping and magnetic anisotropy of ferromagnetic GaMnAs thin films
|
The magnetic properties of annealed, epitaxial Ga0.93Mn0.07As layers under
tensile and compressive stress have been investigated by X-band (9GHz) and
Q-band (35GHz) ferromagnetic resonance (FMR) spectroscopy. From the analysis of
the linewidths of the uniform mode spectra the FMR Gilbert damping factor
"alpha" has been determined. At T=4K we obtain a minimum damping factor of
"alpha" = 0.003 for the compressively stressed layer. Its value is not
isotropic. It has a minimum value for the easy axes orientations of the
magnetic field and increases with the measuring temperature. Its average value
is for both type of films of the order of 0.01 in spite of strong differences
in the inhomogeneous linewidth which vary between 20 Oe and 600 Oe for the
layers grown on GaAs and GaInAs substrates respectively.
|
0809.4644v2
|
2013-08-02
|
Spin pumping damping and magnetic proximity effect in Pd and Pt spin-sink layers
|
We investigated the spin pumping damping contributed by paramagnetic layers
(Pd, Pt) in both direct and indirect contact with ferromagnetic
Ni$_{81}$Fe$_{19}$ films. We find a nearly linear dependence of the
interface-related Gilbert damping enhancement $\Delta\alpha$ on the heavy-metal
spin-sink layer thicknesses t$_\textrm{N}$ in direct-contact
Ni$_{81}$Fe$_{19}$/(Pd, Pt) junctions, whereas an exponential dependence is
observed when Ni$_{81}$Fe$_{19}$ and (Pd, Pt) are separated by \unit[3]{nm} Cu.
We attribute the quasi-linear thickness dependence to the presence of induced
moments in Pt, Pd near the interface with Ni$_{81}$Fe$_{19}$, quantified using
X-ray magnetic circular dichroism (XMCD) measurements. Our results show that
the scattering of pure spin current is configuration-dependent in these systems
and cannot be described by a single characteristic length.
|
1308.0450v2
|
2015-02-05
|
Nonlinear analysis of magnetization dynamics excited by spin Hall effect
|
We investigate the possibility of exciting self-oscillation in a
perpendicular ferromagnet by the spin Hall effect on the basis of a nonlinear
analysis of the Landau-Lifshitz-Gilbert (LLG) equation. In the self-oscillation
state, the energy supplied by the spin torque during a precession on a constant
energy curve should equal the dissipation due to damping. Also, the current to
balance the spin torque and the damping torque in the self-oscillation state
should be larger than the critical current to destabilize the initial state. We
find that the second condition in the spin Hall system is not satisfied by
deriving analytical solutions of the energy supplied by the spin transfer
effect and the dissipation due to the damping from the nonlinear LLG equation.
This indicates that the self-oscillation of a perpendicular ferromagnet cannot
be excited solely by the spin Hall torque.
|
1502.01420v2
|
2015-03-04
|
Critical current destabilizing perpendicular magnetization by the spin Hall effect
|
The critical current needed to destabilize the magnetization of a
perpendicular ferromagnet via the spin Hall effect is studied. Both the
dampinglike and fieldlike torques associated with the spin current generated by
the spin Hall effect is included in the Landau-Lifshitz-Gilbert equation to
model the system. In the absence of the fieldlike torque, the critical current
is independent of the damping constant and is much larger than that of
conventional spin torque switching of collinear magnetic systems, as in
magnetic tunnel junctions. With the fieldlike torque included, we find that the
critical current scales with the damping constant as $\alpha^{0}$ (i.e.,
damping independent),$\alpha$, and $\alpha^{1/2}$ depending on the sign of the
fieldlike torque and other parameters such as the external field. Numerical and
analytical results show that the critical current can be significantly reduced
when the fieldlike torque possesses the appropriate sign, i.e. when the
effective field associated with the fieldlike torque is pointing opposite to
the spin direction of the incoming electrons. These results provide a pathway
to reducing the current needed to switch magnetization using the spin Hall
effect.
|
1503.01478v2
|
2015-10-23
|
Laser-induced THz magnetization precession for a tetragonal Heusler-like nearly compensated ferrimagnet
|
Laser-induced magnetization precessional dynamics was investigated in
epitaxial films of Mn$_3$Ge, which is a tetragonal Heusler-like nearly
compensated ferrimagnet. The ferromagnetic resonance (FMR) mode was observed,
the precession frequency for which exceeded 0.5 THz and originated from the
large magnetic anisotropy field of approximately 200 kOe for this ferrimagnet.
The effective damping constant was approximately 0.03. The corresponding
effective Landau-Lifshitz constant of approximately 60 Mrad/s and is comparable
to those of the similar Mn-Ga materials. The physical mechanisms for the
Gilbert damping and for the laser-induced excitation of the FMR mode were also
discussed in terms of the spin-orbit-induced damping and the laser-induced
ultrafast modulation of the magnetic anisotropy, respectively.
|
1510.06793v1
|
2017-04-11
|
CoFeAlB alloy with low damping and low magnetization for spin transfer torque switching
|
We investigate the effect of Al doping on the magnetic properties of the
alloy CoFeB. Comparative measurements of the saturation magnetization, the
Gilbert damping parameter $\alpha$ and the exchange constant as a function of
the annealing temperature for CoFeB and CoFeAlB thin films are presented. Our
results reveal a strong reduction of the magnetization for CoFeAlB in
comparison to CoFeB. If the prepared CoFeAlB films are amorphous, the damping
parameter $\alpha$ is unaffected by the Al doping in comparison to the CoFeB
alloy. In contrast, in the case of a crystalline CoFeAlB film, $\alpha$ is
found to be reduced. Furthermore, the x-ray characterization and the evolution
of the exchange constant with the annealing temperature indicate a similar
crystallization process in both alloys. The data proves the suitability of
CoFeAlB for spin torque switching properties where a reduction of the switching
current in comparison with CoFeB is expected.
|
1704.03326v1
|
2018-09-25
|
Theory of damping in magnetization dynamics, dispelling a myth and pointing a way forward
|
There is a widely-held belief amongst theoreticians that the Gilbert damping
parameter {\alpha} in magnetization dynamics is infinite for a pure metal at
T=0. The basic error leading to this belief is pointed out explicitly and the
various methods of calculation used are viewed in a unified way based on the
Lorentzian lineshape of ferromagnetic resonance spectra. A general torque
formula for {\alpha} is proposed as a good starting-point for treating
inhomogeneous materials such as alloys, compounds and layered structures. Local
spin density functional theory provides a simple physical picture, in terms of
a non-uniform precessional cone angle in ferromagnetic resonance, of how such
inhomogeneity contributes to the damping. In a complementary many-body theory
this contribution is given by a vertex correction to the torque-torque response
function.
|
1809.09429v1
|
2018-10-31
|
Anisotropic and controllable Gilbert-Bloch dissipation in spin valves
|
Spin valves form a key building block in a wide range of spintronic concepts
and devices from magnetoresistive read heads to spin-transfer-torque
oscillators. We elucidate the dependence of the magnetic damping in the free
layer on the angle its equilibrium magnetization makes with that in the fixed
layer. The spin pumping-mediated damping is anisotropic and tensorial, with
Gilbert- and Bloch-like terms. Our investigation reveals a mechanism for tuning
the free layer damping in-situ from negligible to a large value via the
orientation of fixed layer magnetization, especially when the magnets are
electrically insulating. Furthermore, we expect the Bloch contribution that
emerges from the longitudinal spin accumulation in the non-magnetic spacer to
play an important role in a wide range of other phenomena in spin valves.
|
1811.00020v2
|
2019-07-27
|
Two improved Gauss-Seidel projection methods for Landau-Lifshitz-Gilbert equation
|
In this paper, we present two improved Gauss-Seidel projection methods with
unconditional stability. The first method updates the gyromagnetic term and the
damping term simultaneously and follows by a projection step. The second method
introduces two sets of approximate solutions, where we update the gyromagnetic
term and the damping term simultaneously for one set of approximate solutions
and apply the projection step to the other set of approximate solutions in an
alternating manner. Compared to the original Gauss-Seidel projection method
which has to solve heat equations $7$ times at each time step, the improved
methods solve heat equations $5$ times and $3$ times, respectively. First-order
accuracy in time and second-order accuracy in space are verified by examples in
both 1D and 3D. In addition, unconditional stability with respect to both the
grid size and the damping parameter is confirmed numerically. Application of
both methods to a realistic material is also presented with hysteresis loops
and magnetization profiles. Compared with the original method, the recorded
running times suggest that savings of both methods are about $2/7$ and $4/7$
for the same accuracy requirement, respectively.
|
1907.11853v1
|
2020-10-01
|
Modeling coupled spin and lattice dynamics
|
A unified model of molecular and atomistic spin dynamics is presented
enabling simulations both in microcanonical and canonical ensembles without the
necessity of additional phenomenological spin damping. Transfer of energy and
angular momentum between the lattice and the spin systems is achieved by a
coupling term based upon the spin-orbit interaction. The characteristic spectra
of the spin and phonon systems are analyzed for different coupling strength and
temperatures. The spin spectral density shows magnon modes together with the
uncorrelated noise induced by the coupling to the lattice. The effective
damping parameter is investigated showing an increase with both coupling
strength and temperature. The model paves the way to understanding magnetic
relaxation processes beyond the phenomenological approach of the Gilbert
damping and the dynamics of the energy transfer between lattice and spins.
|
2010.00642v1
|
2021-04-22
|
Impact of Fe$_{80}$B$_{20}$ insertion on the properties of dual-MgO perpendicular magnetic tunnel junctions
|
We explore the impact of Fe80B20 inserted at both
Co$_{20}$Fe$_{80}$B$_{20}$/MgO interfaces of dual-MgO free layers (FLs) in
bottom-pinned magnetic tunnel junctions (MTJs). MTJ stacks are annealed for 30
min at 350 $^\circ$C and 400 $^\circ$C in a vacuum after film deposition.
Current-in-plane tunneling measurements are carried out to characterize
magnetotransport properties of the MTJs. Conventional magnetometry measurements
and ferromagnetic resonance are conducted to estimate the saturation
magnetization, the effective perpendicular anisotropy field and the Gilbert
damping of dual-MgO FLs as a function of the Fe$_{80}$B$_{20}$ thickness and
annealing temperatures. With ultrathin Fe$_{80}$B$_{20}$ (0.2 - 0.4 nm)
inserted, perpendicular magnetic anisotropy (PMA) of FLs increases with similar
tunnel magneto-resistance (TMR) and low damping values. As Fe$_{80}$B$_{20}$
layer thickness further increases (0.6 - 1.2 nm), both TMR and PMA degrade, and
damping increases dramatically. This study demonstrates a novel approach to
tune properties of MTJ stacks with dual-MgO FLs up to 400 $^\circ$C annealing,
which enables MTJ stacks for various applications.
|
2104.10918v1
|
2021-09-24
|
Damping in yttrium iron garnet film with an interface
|
We report strong damping enhancement in a 200 nm thick yttrium iron garnet
(YIG) film due to spin inhomogeneity at the interface. The growth-induced thin
interfacial gadolinium iron garnet (GdIG) layer antiferromagnetically (AFM)
exchange couples with the rest of the YIG layer. The out-of-plane angular
variation of ferromagnetic resonance (FMR) linewidth $\Delta H$ reflects a
large inhomogeneous distribution of effective magnetization $\Delta 4 \pi
M_{eff}$ due to the presence of an exchange springlike moments arrangement in
YIG. We probe the spin inhomogeneity at the YIG-GdIG interface by performing an
in-plane angular variation of resonance field $H_{r}$, leading to a
unidirectional feature. The large extrinsic $\Delta 4\pi M_{eff}$ contribution,
apart from the inherent intrinsic Gilbert contribution, manifests enhanced
precessional damping in YIG film.
|
2109.12071v1
|
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