Extra stability for magnetic knots
Scientists find a new mechanism for the stabilization of skyrmions

Date:
September 21, 2020
Source:
Kiel University
Summary:
Tiny magnetic whirls that can occur in materials - so-called
skyrmions - hold high promises for novel electronic devices
or magnetic memory in which they are used as bits to store
information. A fundamental prerequisite for any application is
its stability. A research team has now demonstrated that so far
neglected magnetic interactions can play a key role for skyrmion
stability and can drastically enhance their lifetime.



FULL STORY ==========================================================================
Tiny magnetic whirls that can occur in materials -- so-called skyrmions
-- hold high promises for novel electronic devices or magnetic memory
in which they are used as bits to store information. A fundamental
prerequisite for any application is the stability of these magnetic
whirls. A research team of the Institute of Theoretical Physics and Astrophysics of Kiel University has now demonstrated that so far neglected magnetic interactions can play a key role for skyrmion stability and
can drastically enhance skyrmion lifetime. Their work, which has been
published today (September 21, 2020) in Nature Communications, opens
also the perspective to stabilize skyrmions in new material systems in
which the previously considered mechanisms are not sufficient.


========================================================================== Intensive research on stability at room temperature Their unique magnetic structure -- more precisely their topology -- lends stability to skyrmions
and protects them from collapse. Therefore, skyrmions are denoted as
knots in the magnetization. However, on the atomic lattice of a solid
this protection is imperfect and there is only a finite energy barrier.

"The situation is comparable to a marble lying in a trough which thus
needs a certain impetus, energy, to escape from it. The larger the energy barrier, the higher is the temperature at which the skyrmion is stable," explains Professor Stefan Heinze from Kiel University. Especially
skyrmions with diameters below 10 nanometers, which are needed for
future spinelectronic devices, have so far only been detected at very
low temperatures. Since applications are typically at room temperature
the enhancement of the energy barrier is a key objective in today's
research on skyrmions.

Previously, a standard model of the relevant magnetic interactions
contributing to the barrier has been established. A team of theoretical physicists from the research group of Professor Stefan Heinze has now demonstrated that one type of magnetic interactions has so far been
overlooked. In the 1920s Werner Heisenberg could explain the occurrence
of ferromagnetism by the quantum mechanical exchange interaction
which results from the spin dependent "hopping" of electrons between
two atoms. "If one considers the electron hopping between more atoms, higher-order exchange interactions occur," says Dr. Souvik Paul, first
author of the study. However, these interactions are much weaker than
the pair-wise exchange proposed by Heisenberg and were thus neglected
in the research on skyrmions.

Weak higher-order exchange interactions stabilize skyrmions Based on
atomistic simulations and quantum mechanical calculations performed
on the super computers of the North-German Supercomputing Alliance
(HLRN) the scientists from Kiel have now explained that these weak
interactions can still provide a surprisingly large contribution to
skyrmion stability. Especially the cyclic hopping over four atomic sites influences the energy of the transition state extraordinarily strongly,
where only a few atomic bar magnets are tilted against each other. Even
stable antiskyrmions were found in the simulations which are advantageous
for some future data storage concepts but typically decay too fast.

Higher-order exchange interactions appear in many magnetic materials
used for potential skyrmion applications such as cobalt or iron. They can
also stabilize skyrmions in magnetic structures in which the previously considered magnetic interactions cannot occur or are too small. Therefore,
the present study opens new promising routes for the research on these fascinating magnetic knots.


========================================================================== Story Source: Materials provided by Kiel_University. Note: Content may
be edited for style and length.


========================================================================== Journal Reference:
1. Souvik Paul, Soumyajyoti Haldar, Stephan von Malottki, Stefan
Heinze.

Role of higher-order exchange interactions for skyrmion
stability. Nature Communications, 2020; 11 (1) DOI:
10.1038/s41467-020-18473-x ==========================================================================

Link to news story: https://www.sciencedaily.com/releases/2020/09/200921111737.htm

--- up 4 weeks, 6 hours, 50 minutes
* Origin: -=> Castle Rock BBS <=- Now Husky HPT Powered! (1337:3/111)