Skyrmions
(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. This discovery opens up a
new class of materials for scientists working on ‘skyrmionics’, which aims to
build memory and logic devices based on skyrmions. The results are published on
todays Nature Communications.
The field of skyrmionics has developed rapidly over the last
few years. The very small (around 10 nanometre) magnetic vortices could provide
a new way to build memory and logical devices with a very low energy use. ‘In
fact, a computer memory system based on magnetic bubbles, which are basically
very large skyrmions, was invented in the 1967 at Bell Labs’, explains Maxim
Mostovoy, Associate Professor of Theoretical Physics at the University of
Groningen. This bubble memory was rapidly overtaken in the 1980s by much
smaller silicon-based memory and is now only used for niche applications – it
is very robust, has no moving parts and can operate in harsh environments.
Frustrated magnet
So far, skyrmions are only produced in special materials
called chiral magnets. The lattice structure of these magnets is chiral, which
means the crystal lattice does not have the same properties as its mirror
image. ‘To advance the field, new classes of materials are needed’, says
Mostovoy. With his post-doc Andrey Leonov (currently working at the Technische
Universität Dresden), he discovered that magnetic frustration can produce
skyrmions.
In a normal magnet, the magnetic moments are aligned. In a
frustrated magnet, interactions favouring parallel magnetic moments compete
with interactions favouring antiparallel magnetic moments. Mostovoy: ‘This means
the magnetic moments in the crystals are not happy – they are forced to coil
into magnetic spirals.’ An applied magnetic field transforms the spiral into a
magnetic crystal composed of skyrmions.