Neutron scattering clarifies the arrangement of skyrmions in material

June 21, 2017, Australian Nuclear Science and Technology Organisation (ANSTO)
After forming a stable, triangular lattice of skyrmions, RIKEN researchers used an external magnetic field to rearrange the lattice into a square pattern. Credit: Yoichi Nii

Measurements at the Australian Centre for Neutron Scattering have helped clarify the arrangement of magnetic vortices, known as skyrmions, in manganese silicide (MnSi).

A is the smallest possible change in a uniform magnet: a point-like region of reversed magnetisation, surrounded by a whirling twist of spins.

The magnetic configuration is attracting attention as a potential data carrier in next-generation .

A group of researchers at the RIKEN Center for Emergent Matter Science in Japan have discovered that a can be used to switch a group of skyrmions back and forth between two different arrangements, demonstrating the kind of control needed for advanced memory devices.

The study has been published in Science Advances.

The atoms in certain carry their own intrinsic magnetism, with each atom acting like a bar magnet. When these miniature magnets are swept into tiny swirling patterns, they collectively form skyrmions which behave as discrete particles.

It only forms in magnets in which the interaction of spins prefer a magnetic structure with chiral symmetry, such as twist that is either left or right-handed.

Being circular, skyrmions typically pack together in a triangular lattice.

Taro Nakajima and Hiroshi Oike of RIKEN and colleagues studied how this skyrmion lattice can be manipulated in manganese silicide.

Generally, skyrmion lattices appear in this material only within a narrow range of temperatures and magnetic fields. "That makes the lattices too fragile to rearrange," said Nakajima.

The team investigated a more robust skyrmion lattice by applying electrical pulses to the material at 12.5 kelvin (K) and a magnetic field of 0.2 tesla (T).

The pulses rapidly heated the material, causing skyrmions to form in a window of stability between 27 and 29 K.

The sample quickly cooled, locking the skyrmions into a triangular lattice that were stable over a much wider range of temperatures and magnetic fields.

The researchers then cooled the sample to 1.5 K and used small angle neutron scattering (SANS) on the QUOKKA instrument to understand how the skyrmion lattice changed under different magnetic fields.

At magnetic fields below 0.1 T, the lattice re-arranged into a square pattern which was stable only within a relatively confined range of very low temperatures and magnetic fields. Raising the to 0.2 T resurrected the triangular lattice.

"On QUOKKA it was possible to measure changes to the skyrmion lattice in situ when an electric current was applied under different magnetic fields," said instrument scientist Dr Elliot Gilbert, and co-author on the publication.

Although SANS does not see the particle-like properties of skyrmions directly, the patterns can be interpreted to provide information on the packing of the particles.

The researchers suggest that these lattice transitions are influenced by unevenness, or anisotropy, in the underlying magnetism of the manganese atoms in the material.

At low magnetic fields and temperatures, this anisotropy allows the skyrmions to partially overlap, moving closer together to adopt a square lattice arrangement.

This effect could well occur in other materials, according to the research team.

"Our experiments revealed that the skyrmions do indeed have a particle nature in bulk crystals," says Nakajima.

"These are expected to be applicable for future magnetic memory devices in which each skyrmion particle behaves as an information carrier."

Explore further: Study into spirals of magnetic spin showcases potential of layered materials for future data storage

More information: Skyrmion lattice structural transition in MnSi. Science Advances. DOI: 10.1126/sciadv.1602562 ,

Related Stories

The synchronized dance of skyrmion spins

May 30, 2017

In recent years, excitement has swirled around a type of quasi-particle called a skyrmion that arises as a collective behavior of a group of electrons. Because they're stable, only a few nanometers in size, and need just ...

Frustrated magnets point towards new memory

September 23, 2015

Theoretical physicists from the University of Groningen, supported by the FOM Foundation, have discovered that so-called 'frustrated magnets' can produce skyrmions, tiny magnetic vortices that may be used in memory storage. ...

Just a touch of skyrmions

October 13, 2015

Ancient memory devices such as handwriting were based on mechanical energy—but in the modern world they have given way to devices based generally on electrical manipulation.

Recommended for you

New thermoelectric material delivers record performance

January 17, 2019

Taking advantage of recent advances in using theoretical calculations to predict the properties of new materials, researchers reported Thursday the discovery of a new class of half-Heusler thermoelectric compounds, including ...

Zirconium isotope a master at neutron capture

January 17, 2019

The probability that a nucleus will absorb a neutron is important to many areas of nuclear science, including the production of elements in the cosmos, reactor performance, nuclear medicine and defense applications.

Mechanism helps explain the ear's exquisite sensitivity

January 16, 2019

The human ear, like those of other mammals, is so extraordinarily sensitive that it can detect sound-wave-induced vibrations of the eardrum that move by less than the width of an atom. Now, researchers at MIT have discovered ...


Please sign in to add a comment. Registration is free, and takes less than a minute. Read more

Click here to reset your password.
Sign in to get notified via email when new comments are made.