Skyrmion research: Braids of nanovortices discovered

Date:
October 6, 2021
Source:
Forschungszentrum Juelich
Summary:
A team of scientists has discovered a new physical phenomenon:
complex braided structures made of tiny magnetic vortices known
as skyrmions.

Skyrmions were first detected experimentally a little over a
decade ago and have since been the subject of numerous studies,
as well as providing a possible basis for innovative concepts
in information processing that offer better performance and
lower energy consumption. Furthermore, skyrmions influence the
magnetoresistive and thermodynamic properties of a material. The
discovery therefore has relevance for both applied and basic
research.



FULL STORY ==========================================================================
A team of scientists from Germany, Sweden and China has discovered a new physical phenomenon: complex braided structures made of tiny magnetic
vortices known as skyrmions. Skyrmions were first detected experimentally
a little over a decade ago and have since been the subject of numerous
studies, as well as providing a possible basis for innovative concepts
in information processing that offer better performance and lower energy consumption. Furthermore, skyrmions influence the magnetoresistive and thermodynamic properties of a material. The discovery therefore has
relevance for both applied and basic research.


========================================================================== Strings, threads and braided structures can be seen everywhere in daily
life, from shoelaces, to woollen pullovers, from plaits in a child's
hair to the braided steel cables that are used to support countless
bridges. These structures are also commonly seen in nature and can, for example, give plant fibres tensile or flexural strength. Physicists at Forschungszentrum Ju"lich, together with colleagues from Stockholm and
Hefei, have discovered that such structures exist on the nanoscale in
alloys of iron and the metalloid germanium.

These nanostrings are each made up of several skyrmions that are twisted together to a greater or lesser extent, rather like the strands of a
rope. Each skyrmion itself consists of magnetic moments that point in
different directions and together take the form of an elongated tiny
vortex. An individual skyrmion strand has a diamater of less than one micrometre. The length of the magnetic structures is limited only by the thickness of the sample; they extend from one surface of the sample to
the opposite surface.

Earlier studies by other scientists had shown that such filaments are
largely linear and almost rod-shaped. However, ultra-high-resolution
microscopy investigations undertaken at the Ernst Ruska-Centre in Ju"lich
the theoretical studies at Ju"lich's Peter Gru"nberg Institute have
revealed a more varied picture: the threads can in fact twist together
to varying degrees. According to the researchers, these complex shapes stabilise the magnetic structures, making them particularly interesting
for use in a range of applications.

"Mathematics contains a great variety of these structures. Now we
know that this theoretical knowledge can be translated into real
physical phenomena," Ju"lich physicist Dr. Nikolai Kiselev is pleased
to report. "These types of structures inside magnetic solids suggest
unique electrical and magnetic properties. However, further research
is needed to verify this." To explain the discrepancy between these
studies and previous ones, the researcher points out that analyses using
an ultra-high-resolution electron microscope do not simply provide
an image of the sample, as in the case of, for example, an optical
microscope. This is because quantum mechanical phenomena come into play
when the high energy electrons interact with those in the sample.

"It is quite feasible that other researchers have also seen these
structures under the microscope, but have been unable to interpret
them. This is because it is not possible to directly determine the
distribution of magnetization directions in the sample from the data
obtained. Instead, it is necessary to create a theoretical model of the
sample and to generate a kind of electron microscope image from it,"
explains Kiselev. "If the theoretical and experimental images match,
one can conclude that the model is able to represent reality." In ultra-high-resolution analyses of this kind, Forschungszentrum Ju"lich
with its Ernst Ruska-Centre counts as one of the leading institutions worldwide.

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


========================================================================== Journal Reference:
1. Fengshan Zheng, Filipp N. Rybakov, Nikolai S. Kiselev, Dongsheng
Song,
Andra's Kova'cs, Haifeng Du, Stefan Blu"gel & Rafal
E. Dunin-Borkowski.

Magnetic skyrmion braids. Nature Communications, 2021 DOI: 10.1038/
s41467-021-25389-7 ==========================================================================

Link to news story: https://www.sciencedaily.com/releases/2021/10/211006112630.htm

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