3,349 research outputs found
Influence of magnetic viscosity on domain wall dynamics under spin-polarized currents
We present a theoretical study of the influence of magnetic viscosity on
current-driven domain wall dynamics. In particular we examine how domain wall
depinning transitions, driven by thermal activation, are influenced by the
adiabatic and nonadiabatic spin-torques. We find the Arrhenius law that
describes the transition rate for activation over a single energy barrier
remains applicable under currents but with a current-dependent barrier height.
We show that the effective energy barrier is dominated by a linear current
dependence under usual experimental conditions, with a variation that depends
only on the nonadiabatic spin torque coefficient beta.Comment: 8 pages, 4 figure
On quantifying the topological charge in micromagnetics using a lattice-based approach
An implementation of a lattice-based approach for computing the topological
skyrmion charge is provided for the open source micromagnetics code MuMax3. Its
accuracy with respect to an existing method based on finite difference
derivatives is compared for three different test cases. The lattice-based
approach is found to be more robust for finite-temperature dynamics and for
nucleation and annihilation processes in extended systems.Comment: 9 pages, 5 figure
Trochoidal motion and pair generation in skyrmion and antiskyrmion dynamics under spin-orbit torques
Skyrmions and antiskyrmions in magnetic ultrathin films are characterised by
a topological charge describing how the spins wind around their core. This
topology governs their response to forces in the rigid core limit. However,
when internal core excitations are relevant, the dynamics become far richer. We
show that current-induced spin-orbit torques can lead to phenomena such as
trochoidal motion and skyrmion-antiskyrmion pair generation that only occurs
for either the skyrmion or antiskyrmion, depending on the symmetry of the
underlying Dzyaloshinskii-Moriya interaction. Such dynamics are induced by core
deformations, leading to a time-dependent helicity that governs the motion of
the skyrmion and antiskyrmion core. We compute the dynamical phase diagram
through a combination of atomistic spin simulations, reduced-variable
modelling, and machine learning algorithms. It predicts how spin-orbit torques
can control the type of motion and the possibility to generate skyrmion
lattices by antiskyrmion seeding
Temperature dependence of nonlinear auto-oscillator linewidths: Application to spin-torque nano-oscillators
The temperature dependence of the generation linewidth for an auto-oscillator
with a nonlinear frequency shift is calculated. It is shown that the frequency
nonlinearity creates a finite correlation time, tau, for the phase
fluctuations. In the low-temperature limit in which the spectral linewidth is
smaller than 1/tau, the line shape is approximately Lorentzian and the
linewidth is linear in temperature. In the opposite high-temperature limit in
which the linewidth is larger than 1/tau, the nonlinearity leads to an apparent
"inhomogeneous broadening" of the line, which becomes Gaussian in shape and has
a square-root dependence on temperature. The results are illustrated for the
spin-torque nano-oscillator.Comment: 4 pages, 1 figur
Generation linewidth of an auto-oscillator with a nonlinear frequency shift: Spin-torque nano-oscillator
It is shown that the generation linewidth of an auto-oscillator with a
nonlinear frequency shift (i.e. an auto-oscillator in which frequency depends
on the oscillation amplitude) is substantially larger than the linewidth of a
conventional quasi-linear auto-oscillator due to the renormalization of the
phase noise caused by the nonlinearity of the oscillation frequency. The
developed theory, when applied to a spin-torque nano-contact auto-oscillator,
predicts a minimum of the generation linewidth when the nano-contact is
magnetized at a critical angle to its plane, corresponding to the minimum
nonlinear frequency shift, in good agreement with recent experiments.Comment: 4 pages, 2 figure
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