1,910 research outputs found
Orientation dependent current-induced motion of skyrmions with various topologies
We study the current-driven motion of metastable localized spin structures
with various topological charges in a (PtIr)/Fe bilayer on a
Pd(111) surface by combining atomistic spin model simulations with an approach
based on the generalized Thiele equation. We demonstrate that besides a
distinct dependence on the topological charge itself the dynamic response of
skyrmionic structures with topological charges and
to a spin-polarized current exhibits an orientation dependence.
We further show that such an orientation dependence can be induced by applying
an in-plane external field, possibly opening up a new pathway to the
manipulation of skyrmion dynamics
Unfaithful Glitch Propagation in Existing Binary Circuit Models
We show that no existing continuous-time, binary value-domain model for
digital circuits is able to correctly capture glitch propagation. Prominent
examples of such models are based on pure delay channels (P), inertial delay
channels (I), or the elaborate PID channels proposed by Bellido-D\'iaz et al.
We accomplish our goal by considering the solvability/non-solvability border of
a simple problem called Short-Pulse Filtration (SPF), which is closely related
to arbitration and synchronization. On one hand, we prove that SPF is solvable
in bounded time in any such model that provides channels with non-constant
delay, like I and PID. This is in opposition to the impossibility of solving
bounded SPF in real (physical) circuit models. On the other hand, for binary
circuit models with constant-delay channels, we prove that SPF cannot be solved
even in unbounded time; again in opposition to physical circuit models.
Consequently, indeed none of the binary value-domain models proposed so far
(and that we are aware of) faithfully captures glitch propagation of real
circuits. We finally show that these modeling mismatches do not hold for the
weaker eventual SPF problem.Comment: 23 pages, 15 figure
Temperature scaling of the Dzyaloshinsky-Moriya interaction in the spin wave spectrum
The temperature scaling of the micromagnetic Dzyaloshinsky-Moriya exchange
interaction is calculated for the whole range of temperature. We use Green's
function theory to derive the finite-temperature spin wave spectrum of
ferromagnetic systems described by a classical atomistic spin model
Hamiltonian. Within this model, we find universal expressions for the
temperature scaling not only of the Dzyaloshinsky-Moriya interaction but also
of the Heisenberg exchange stiffness and the single-ion anisotropy. In the
spirit of multiscale models, we establish a clear connection between the
atomistic interactions and the temperature-dependent coefficients in the spin
wave spectrum and in the micromagnetic free energy functional. We demonstrate
that the corrections to mean-field theory or the random phase approximation for
the temperature scaling of Dzyaloshinsky-Moriya and Heisenberg exchange
interactions assume very similar forms. In the presence of thermal fluctuations
and Dzyaloshinsky-Moriya interaction an anisotropy-like term emerges in the
spin wave spectrum which, at low temperature, increases with temperature, in
contrast to the decreasing single-ion anisotropy. We evaluate the accuracy of
the theoretical method by comparing it to the spin wave spectrum calculated
from Monte Carlo simulations.Comment: 11 pages, 4 figure
Reduced thermal stability of antiferromagnetic nanostructures
Antiferromagnetic materials hold promising prospects in novel types of
spintronics applications. Assessing the stability of antiferromagnetic
nanostructures against thermal excitations is a crucial aspect of designing
devices with a high information density. Here we use theoretical calculations
and numerical simulations to determine the mean switching time of
antiferromagnetic nanoparticles in the superparamagnetic limit. It is
demonstrated that the thermal stability is drastically reduced compared to
ferromagnetic particles in the limit of low Gilbert damping, attributed to the
exchange enhancement of the attempt frequencies. It is discussed how the system
parameters have to be engineered in order to optimize the switching rates in
antiferromagnetic nanoparticles.Comment: 12 pages, 6 figures. Supplemental Videos available with the published
versio
Spin waves cause non-linear friction
Energy dissipation is studied for a hard magnetic tip that scans a soft
magnetic substrate. The dynamics of the atomic moments are simulated by solving
the Landau-Lifshitz-Gilbert (LLG) equation numerically. The local energy
currents are analysed for the case of a Heisenberg spin chain taken as
substrate. This leads to an explanation for the velocity dependence of the
friction force: The non-linear contribution for high velocities can be
attributed to a spin wave front pushed by the tip along the substrate.Comment: 5 pages, 9 figure
Spin waves cause non-linear friction
Energy dissipation is studied for a hard magnetic tip that scans a soft
magnetic substrate. The dynamics of the atomic moments are simulated by solving
the Landau-Lifshitz-Gilbert (LLG) equation numerically. The local energy
currents are analysed for the case of a Heisenberg spin chain taken as
substrate. This leads to an explanation for the velocity dependence of the
friction force: The non-linear contribution for high velocities can be
attributed to a spin wave front pushed by the tip along the substrate.Comment: 5 pages, 9 figure
Magnetic field control of the spin Seebeck effect
The origin of the suppression of the longitudinal spin Seebeck effect by
applied magnetic fields is studied. We perform numerical simulations of the
stochastic Landau-Lifshitz-Gilbert equation of motion for an atomistic spin
model and calculate the magnon accumulation in linear temperature gradients for
different strengths of applied magnetic fields and different length scales of
the temperature gradient. We observe a decrease of the magnon accumulation with
increasing magnetic field and we reveal that the origin of this effect is a
field dependent change of the frequency distribution of the propagating
magnons. With increasing field the magnonic spin currents are reduced due to a
suppression of parts of the frequency spectrum. By comparison with measurements
of the magnetic field dependent longitudinal spin Seebeck effect in YIG thin
films with various thicknesses, we find that our model describes the
experimental data very well, demonstrating the importance of this effect for
experimental systems
Interfacial exchange interactions and magnetism of Ni2MnAl/Fe bilayers
Based on a multi-scale calculations, combining ab-initio methods with spin
dynamics simulations, we perform a detailed study of the magnetic behavior of
Ni2MnAl/Fe bilayers. Our simulations show that such a bilayer exhibits a small
exchange bias effect when the Ni2MnAl Heusler alloy is in a disordered B2
phase. Additionally, we present an effective way to control the magnetic
structure of the Ni2MnAl antiferromagnet, in the pseudo-ordered B2-I as well as
the disordered B2 phases, via a spin-flop coupling to the Fe layer.Comment: 7 pages, 6 figure
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