5,765 research outputs found
Spin Motion in Electron Transmission through Ultrathin Ferromagnetic Films Accessed by Photoelectron Spectroscopy
Ab initio and model calculations demonstrate that the spin motion of
electrons transmitted through ferromagnetic films can be analyzed in detail by
means of angle- and spin-resolved core-level photoelectron spectroscopy. The
spin motion appears as precession of the photoelectron spin polarization around
and as relaxation towards the magnetization direction. In a systematic study
for ultrathin Fe films on Pd(001) we elucidate its dependence on the Fe film
thickness and on the Fe electronic structure. In addition to elastic and
inelastic scattering, the effect of band gaps on the spin motion is addressed
in particular.Comment: 4 pages, 5 figure
Specific heat of the simple-cubic Ising model
We provide an expression quantitatively describing the specific heat of the
Ising model on the simple-cubic lattice in the critical region. This expression
is based on finite-size scaling of numerical results obtained by means of a
Monte Carlo method. It agrees satisfactorily with series expansions and with a
set of experimental results. Our results include a determination of the
universal amplitude ratio of the specific-heat divergences at both sides of the
critical point.Comment: 20 pages, 3 figure
Tunable chiral spin texture in magnetic domain-walls
Magnetic domain-walls (DWs) with a preferred chirality exhibit very efficient
current-driven motion. Since structural inversion asymmetry (SIA) is required
for their stability, the observation of chiral domain walls in highly symmetric
Pt/Co/Pt is intriguing. Here, we tune the layer asymmetry in this system and
observe, by current-assisted DW depinning experiments, a small chiral field
which sensitively changes. Moreover, we convincingly link the observed
efficiency of DW motion to the DW texture, using DW resistance as a direct
probe for the internal orientation of the DW under the influence of in-plane
fields. The very delicate effect of capping layer thickness on the chiral field
allows for its accurate control, which is important in designing novel
materials for optimal spin-orbit-torque-driven DW motion.Comment: 12 pages, 5 figure
Controlling skyrmion bubble confinement by dipolar interactions
Large skyrmion bubbles in confined geometries of various sizes and shapes are
investigated, typically in the range of several micrometers. Two fundamentally
different cases are studied to address the role of dipole-dipole interactions:
(I) when there is no magnetic material present outside the small geometries and
(II) when the geometries are embedded in films with a uniform magnetization. It
is found that the preferential position of the skyrmion bubbles can be
controlled by the geometrical shape, which turns out to be a stronger influence
than local variations in material parameters. In addition, independent
switching of the direction of the magnetization outside the small geometries
can be used to further manipulate these preferential positions, in particular
with respect to the edges. We show by numerical calculations that the observed
interactions between the skyrmion bubbles and structure edge including the
overall positioning of the bubbles are fully controlled by dipole-dipole
interactions
Strong influence of the complex bandstructure on the tunneling electroresistance: A combined model and ab-initio study
The tunneling electroresistance (TER) for ferroelectric tunnel junctions
(FTJs) with BaTiO_{3} (BTO) and PbTiO}_{3} (PTO) barriers is calculated by
combining the microscopic electronic structure of the barrier material with a
macroscopic model for the electrostatic potential which is caused by the
ferroelectric polarization. The TER ratio is investigated in dependence on the
intrinsic polarization, the chemical potential, and the screening properties of
the electrodes. A change of sign in the TER ratio is obtained for both barrier
materials in dependence on the chemical potential. The inverse imaginary Fermi
velocity describes the microscopic origin of this effect; it qualitatively
reflects the variation and the sign reversal of the TER. The quantity of the
imaginary Fermi velocity allows to obtain detailed information on the transport
properties of FTJs by analyzing the complex bandstructure of the barrier
material.Comment: quality of figures reduce
A Unifying Framework for Strong Structural Controllability
This paper deals with strong structural controllability of linear systems. In
contrast to existing work, the structured systems studied in this paper have a
so-called zero/nonzero/arbitrary structure, which means that some of the
entries are equal to zero, some of the entries are arbitrary but nonzero, and
the remaining entries are arbitrary (zero or nonzero). We formalize this in
terms of pattern matrices whose entries are either fixed zero, arbitrary
nonzero, or arbitrary. We establish necessary and sufficient algebraic
conditions for strong structural controllability in terms of full rank tests of
certain pattern matrices. We also give a necessary and sufficient graph
theoretic condition for the full rank property of a given pattern matrix. This
graph theoretic condition makes use of a new color change rule that is
introduced in this paper. Based on these two results, we then establish a
necessary and sufficient graph theoretic condition for strong structural
controllability. Moreover, we relate our results to those that exists in the
literature, and explain how our results generalize previous work.Comment: 11 pages, 6 Figure
Activated sampling in complex materials at finite temperature: the properly-obeying-probability activation-relaxation technique
While the dynamics of many complex systems is dominated by activated events,
there are very few simulation methods that take advantage of this fact. Most of
these procedures are restricted to relatively simple systems or, as with the
activation-relaxation technique (ART), sample the conformation space
efficiently at the cost of a correct thermodynamical description. We present
here an extension of ART, the properly-obeying-probability ART (POP-ART), that
obeys detailed balance and samples correctly the thermodynamic ensemble.
Testing POP-ART on two model systems, a vacancy and an interstitial in
crystalline silicon, we show that this method recovers the proper
thermodynamical weights associated with the various accessible states and is
significantly faster than MD in the diffusion of a vacancy below 700 K.Comment: 10 pages, 3 figure
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