101 research outputs found
Forming individual magnetic biskyrmions by merging two skyrmions in a centrosymmetric nanodisk
When two magnetic skyrmions - whirl-like, topologically protected
quasiparticles - form a bound pair, a biskyrmion state with a topological
charge of is constituted. Recently, especially the case
of two partially overlapping skyrmions has brought about great research
interest. Since for its formation the individual skyrmions need to posses
opposite in-plane magnetizations, such a biskyrmion cannot be stabilized by the
Dzyaloshinskii-Moriya-interaction (DMI), which is the interaction that
typically stabilizes skyrmions in non-centrosymmetric materials and at
interfaces. Here, we show that these biskyrmions can be stabilized by the
dipole-dipole interaction in centrosymmetric materials in which the DMI is
forbidden. Analytical considerations indicate that the bound state of a
biskyrmion is energetically preferable over two individual skyrmions. As a
result, when starting from two skyrmions in a micromagnetic simulation, a
biskyrmion is formed upon relaxation. We propose a scheme that allows to
control this biskyrmion formation in nanodisks and analyze the individual
steps.Comment: This is a post-peer-review, pre-copyedit version of an article
published in Scientific Reports. The final authenticated version is available
online at [DOI
Phonon limited thermoelectric transport in Pb
We present a fully ab initio based scheme to compute transport properties,
i.e. the electrical conductivity {\sigma} and thermopower S, in the presence of
electron-phonon interaction. Therefore, we explicitly investigate the
k-dependent structure of the Eliashberg spectral function , the coupling
strength, the linewidth and the relaxation time {\tau}. We obtain a
state-dependent {\tau} and show its necessity to reproduce the increased
thermopower at temperatures below the Debye temperature, without accounting for
the phonon-drag effect. Despite the detailed investigations of various k and q
dependencies, the presented scheme can be easily applied to more complicated
systems.Comment: 9 pages, 10 figures, supplemental material adde
Quaternary-digital data storage based on magnetic bubbles in anisotropic materials
The topologically non-trivial nano-whirls, called magnetic skyrmions, are
often considered attractive for spintronic applications like the racetrack data
storage device. However, skyrmions do not move parallel to applied currents and
typically do not coexist with other nano-objects, making the realization of
such storage concepts difficult. Herein we consider materials with an
anisotropic DMI, like tetragonal Heusler materials, and show that four distinct
types of topologically trivial bubbles can coexist. We show that each of them
can be written by spin torques and that they can be distinguished using a
single magnetic tunneling junction. Due to their trivial topology, the four
types of bubbles move parallel to applied electrical currents and remain
equidistant under motion. Still, the bubbles have a small size and high
stability comparable to topologically non-trivial spin textures. This allows to
construct a quaternary-digit-based racetrack storage device that overcomes the
two mentioned drawbacks of skyrmion-based racetracks.Comment: 6 pages, 3 figure
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