Nanostructures with a unique property

Date:
September 23, 2020
Source:
Paul Scherrer Institute
Summary:
Nanoscale vortices known as skyrmions can be created in many
magnetic materials. For the first time, researchers have managed
to create and identify antiferromagnetic skyrmions with a unique
property: critical elements inside them are arranged in opposing
directions. Scientists have succeeded in visualizing this phenomenon
using neutron scattering.



FULL STORY ========================================================================== Nanoscale vortices known as skyrmions can be created in many magnetic materials. For the first time, researchers at PSI have managed to create
and identify antiferromagnetic skyrmions with a unique property: critical elements inside them are arranged in opposing directions. Scientists have succeeded in visualising this phenomenon using neutron scattering. Their discovery is a major step towards developing potential new applications,
such as more efficient computers. The results of the research are
published today in the journal Nature.


========================================================================== Whether a material is magnetic depends on the spins of its atoms. The best
way to think of spins is as minute bar magnets. In a crystal structure
where the atoms have fixed positions in a lattice, these spins can be
arranged in criss- cross fashion or aligned all in parallel like the
spears of a Roman legion, depending on the individual material and
its state.

Under certain conditions it is possible to generate tiny vortices
within the corps of spins. These are known as skyrmions. Scientists
are particularly interested in skyrmions as a key component in future technologies, such as more efficient data storage and transfer. For
example, they could be used as memory bits: a skyrmion could represent
the digital one, and its absence a digital zero. As skyrmions are
significantly smaller than the bits used in conventional storage media,
data density is much higher and potentially also more energy efficient,
while read and write operations would be faster as well. Skyrmions could therefore be useful both in classical data processing and in cutting-edge quantum computing.

Another interesting aspect for the application is that skyrmions can
be created and controlled in many materials by applying an electrical
current. "With existing skyrmions, however, it is tricky to move them systematically from A to B, as they tend to deviate from a straight path
due to their inherent properties," explains Oksana Zaharko, research
group leader at PSI.

Working with researchers from other institutions, Dr Zaharko and her
team have now created a new type of skyrmion and demonstrated a unique characteristic: in their interior, critical spins are arranged in
opposite directions to one another. The researchers therefore describe
their skyrmions as antiferromagnetic.

In a straight line from A to B "One of the key advantages of
antiferromagnetic skyrmions is that they are much simpler to control: if
an electrical current is applied, they move in a simple straight line,"
Zaharko comments. This is a major advantage: for skyrmions to be suitable
for practical applications, it must be possible to selectively manipulate
and position them.



==========================================================================
The scientists created their new type of skyrmion by fabricating
them in a customised antiferromagnetic crystal. Zaharko explains: "Antiferromagnetic means that adjacent spins are in an antiparallel arrangement, in other words one pointing upwards and the next pointing downwards. So what was initially observed as a property of the material
we subsequently identified within the individual skyrmions as well."
Several steps are still needed before antiferromagnetic skyrmions are
mature enough for a technological application: PSI researchers had to
cool the crystal down to around minus 272 degrees Celsius and apply an extremely strong magnetic field of three tesla -- roughly 100,000 times
the strength of the Earth's magnetic field.

Neutron scattering to visualise the skyrmions And the researchers have
yet to create individual antiferromagnetic skyrmions.

To verify the tiny vortices, the scientists are using the Swiss Spallation Neutron Source SINQ at PSI. "Here we can visualise skyrmions using
neutron scattering if we have a lot of them in a regular pattern in a particular material," Zaharko explains.

But the scientist is optimistic: "In my experience, if we manage to create skyrmions in a regular alignment, someone will soon manage to create
such skyrmions individually." The general consensus in the research
community is that once individual antiferromagnetic skyrmions can be
created at room temperature, a practical application will not be far off.


========================================================================== Story Source: Materials provided by Paul_Scherrer_Institute. Original
written by Laura Hennemann. Note: Content may be edited for style
and length.


========================================================================== Journal Reference:
1. Shang Gao, H. Diego Rosales, Flavia A. Go'mez Albarraci'n, Vladimir
Tsurkan, Guratinder Kaur, Tom Fennell, Paul Steffens, Martin
Boehm, Petr Čerma'k, Astrid Schneidewind, Eric Ressouche,
Daniel C. Cabra, Christian Ru"egg, Oksana Zaharko. Fractional
antiferromagnetic skyrmion lattice induced by anisotropic
couplings. Nature, 2020; DOI: 10.1038/ s41586-020-2716-8 ==========================================================================

Link to news story: https://www.sciencedaily.com/releases/2020/09/200923124700.htm

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