1,362 research outputs found
Spin motive forces due to magnetic vortices and domain walls
We study spin motive forces, i.e, spin-dependent forces, and voltages induced
by time-dependent magnetization textures, for moving magnetic vortices and
domain walls. First, we consider the voltage generated by a one-dimensional
field-driven domain wall. Next, we perform detailed calculations on
field-driven vortex domain walls. We find that the results for the voltage as a
function of magnetic field differ between the one-dimensional and vortex domain
wall. For the experimentally relevant case of a vortex domain wall, the
dependence of voltage on field around Walker breakdown depends qualitatively on
the ratio of the so-called -parameter to the Gilbert damping constant,
and thus provides a way to determine this ratio experimentally. We also
consider vortices on a magnetic disk in the presence of an AC magnetic field.
In this case, the phase difference between field and voltage on the edge is
determined by the parameter, providing another experimental method to
determine this quantity.Comment: 8 pages, 9 figures, submitted to PR
Anomalous direction for skyrmion bubble motion
Magnetic skyrmions are localized topological excitations that behave as
particles and can be mobile, with great potential for novel data storage
devices. In this work, the current-induced dynamics of large skyrmion bubbles
is studied. When skyrmion motion in the direction opposite to the electron flow
is observed, this is usually interpreted as a perpendicular spin current
generated by the spin Hall effect exerting a torque on the chiral N\'{e}el
skyrmion. By designing samples in which the direction of the net generated spin
current can be carefully controlled, we surprisingly show that skyrmion motion
is always against the electron flow, irrespective of the net vertical
spin-current direction. We find that a negative bulk spin-transfer torque is
the most plausible explanation for the observed results, which is qualitatively
justified by a simple model that captures the essential behaviour. These
findings demonstrate that claims about the skyrmion chirality based on their
current-induced motion should be taken with great caution
Thickness dependence of unidirectional spin-Hall magnetoresistance in metallic bilayers
A nonlinear magnetoresistance - called unidirectional spin-Hall
magnetoresistance - is recently experimentally discovered in metallic bilayers
consisting of a heavy metal and a ferromagnetic metal. To study the fundamental
mechanism of the USMR, both ferromagnetic and heavy metallic layer thickness
dependence of the USMR are presented in a Pt/Co/AlOx trilayer at room
temperature. To avoid ambiguities, second harmonic Hall measurements are used
for separating spin-Hall and thermal contributions to the non-linear
magnetoresistance. The experimental results are fitted by using a
drift-diffusion theory, with parameters extracted from an analysis of
longitudinal resistivity of the Co layer within the framework of the
Fuchs-Sondheimer model. A good agreement with the theory is found,
demonstrating that the USMR is governed by both the spin-Hall effect in the
heavy metallic layer and the metallic diffusion process in the ferromagnetic
layer
Чверть століття на ниві освіти
Наталія Купріянівна Місяць – відомий український вчений-мовознавець, викладач та організатор освіти на Житомирщині. Чверть століття, починаючи вже з далекого 1975 року, життя та діяльність Наталії Куприянівні тісно пов’язані з філологічним факультетом Житомирського едуніверситету імені Івана Франка
Controlling magnetic skyrmion nucleation with Ga+ ion irradiation
In this paper, we show that magnetic skyrmion nucleation can be controlled
using Ga+ ion irradiation, which manipulates the magnetic interface effects (in
particular the magnetic anisotropy and Dzyaloshinskii-Moriya interaction) that
govern the stability and energy cost of skyrmions in thin film systems. We
systematically and quantitatively investigated what effect these changes have
on the nucleation of magnetic skyrmions. Our results indicate that the energy
cost of skyrmion nucleation can be reduced up to 26% in the studied dose range
and that it scales approximately linearly with the square root of the
domain-wall energy density. Moreover, the total number of nucleated skyrmions
in irradiated devices after nucleation was found to depend linearly on the ion
dose and could be doubled compared to nonirradiated devices. These results show
that ion irradiation cannot only be used to enable local nucleation of
skyrmions, but that it also allows for fine control of the threshold and
efficiency of the nucleation process.Comment: Main: 17 pages, 3 figures; Supplemental Material: 7 pages, 5 figure
Accurate extraction of anisotropic spin–orbit torques from harmonic measurements
One of the most powerful ways to manipulate spins in nanometer scale devices is by converting a charge current to a spin current via spin orbit coupling. The resulting spin orbit torques SOTs have been investigated and utilized extensively in the past decade. Quantitatively, however, SOTs may exhibit a non trivial angular dependence which is not well explored. Here, we develop a nested iterative analysis to determine the magnitude of SOTs from harmonic Hall measurements. This updated method largely improves the fit quality in the full magnetic field range and accurately retrieves even higher order, anisotropic spin orbit torque coeficients. The numerical implementation of our algorithm is fast, robust, and designed for easy integration into existing analysis schemes. We verify our code using simulated data with and without anisotropic SOTs. Accurately quantifying higher order SOT terms can be especially useful for modeling non uniform magnetic textures such as domain walls and skyrmions and current induced magnetization switching characteristic
Barrier elision for production parallel programs
Large scientific code bases are often composed of several layers of runtime libraries, implemented in multiple programming languages. In such situation, programmers often choose conservative synchronization patterns leading to suboptimal performance. In this paper, we present context-sensitive dynamic optimizations that elide barriers redundant during the program execution. In our technique, we perform data race detection alongside the program to identify redundant barriers in their calling contexts; after an initial learning, we start eliding all future instances of barriers occurring in the same calling context. We present an automatic on-the-fly optimization and a multi-pass guided optimization. We apply our techniques to NWChem - a 6 million line computational chemistry code written in C/C++/Fortran that uses several runtime libraries such as Global Arrays, ComEx, DMAPP, and MPI. Our technique elides a surprisingly high fraction of barriers (as many as 63%) in production runs. This redundancy elimination translates to application speedups as high as 14% on 2048 cores. Our techniques also provided valuable insight about the application behavior, later used by NWChem developers. Overall, we demonstrate the value of holistic context-sensitive analyses that consider the domain science in conjunction with the associated runtime software stack
Stabilizing chiral spin-structures via an alternating Dzyaloshinskii-Moriya interaction
The stabilization of chiral magnetic spin-structures in thin films is often
attributed to the interfacial Dzyaloshinskii-Moriya interaction (DMI). Very
recently, however, it has been reported that the chirality induced by the DMI
can be affected by dipolar interactions. These dipolar fields tend to form
N\'eel caps, which entails the formation of a clockwise chirality at the top of
the film and a counterclockwise chirality at the bottom. Here, we show that
engineering an alternating DMI that changes sign across the film thickness,
together with the tendency to form N\'eel caps, leads to an enhanced stability
of chiral spin-structures. Micromagnetic simulations for skyrmions demonstrate
that this can increase the effective DMI in a prototypical [Pt/Co/Ir]
multilayer system by at least \SI{0.6}{mJ.m^{-2}}. These gains are comparable
to what has been achieved using additive DMI, but more flexible as we are not
limited to a select set of material combinations. We also present experimental
results: by measuring equilibrium domain widths we quantify the effective DMI
in [Pt/Co/Ir] multilayer systems typically used for skyrmion stabilization.
Upon introducing an alternating DMI we demonstrate changes in the effective DMI
that agree with our simulations. Our results provide a route towards enhancing
the stability of chiral spin-structures that does not rely on enlarging the
chiral interactions.Comment: Includes supplementar
The epidemiology of patellar luxation in dogs attending primary-care veterinary practices in England
Single hadron response measurement and calorimeter jet energy scale uncertainty with the ATLAS detector at the LHC
The uncertainty on the calorimeter energy response to jets of particles is
derived for the ATLAS experiment at the Large Hadron Collider (LHC). First, the
calorimeter response to single isolated charged hadrons is measured and
compared to the Monte Carlo simulation using proton-proton collisions at
centre-of-mass energies of sqrt(s) = 900 GeV and 7 TeV collected during 2009
and 2010. Then, using the decay of K_s and Lambda particles, the calorimeter
response to specific types of particles (positively and negatively charged
pions, protons, and anti-protons) is measured and compared to the Monte Carlo
predictions. Finally, the jet energy scale uncertainty is determined by
propagating the response uncertainty for single charged and neutral particles
to jets. The response uncertainty is 2-5% for central isolated hadrons and 1-3%
for the final calorimeter jet energy scale.Comment: 24 pages plus author list (36 pages total), 23 figures, 1 table,
submitted to European Physical Journal
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