Skyrmions – quasiparticles with a vortex-like structure – can be made to diffuse more than 10 times faster than their natural drift rate in specially-designed materials developed by researchers in Germany and Japan. This speedier movement could come in handy for novel forms of computing that work using random (stochastic) processes like the Brownian motion of particles.
Skyrmions are made up of numerous electron spins and can be thought of as two-dimensional whirls (or “spin textures”) within a material. They exist in many magnetic materials, including cobalt–iron–silicon and the manganese–silicide thin films in which they were first discovered. As well as being of interest in fundamental condensed-matter physics, skyrmions have attracted considerable attention in recent years as a possible basis for future hard-disk technologies.
Today’s hard disks store information in magnetic domains, which are areas where all magnetic spins are aligned in the same direction. There are fundamental restrictions on how small these domains can be, which limits storage capacities. Skyrmions, in contrast, measure just tens of nanometres across, and could therefore be used to create storage devices with much higher densities. A further advantage is that whereas flipping all the spins in conventional domains – to switch a device’s memory state from 1 to 0, for example – requires a considerable amount of power and can be slow, a skyrmion-based switch would require many fewer spin flips. In addition, the final spin state in such a system would be robust against external perturbations, making skyrmion structures more stable than conventional magnetic domains.
Skyrmions can be made to move by applying a small external electric current to a magnetic thin film, but they also move naturally, and randomly, thanks to diffusion. Such stochastic dynamics have attracted much interest recently because they could be exploited to make highly energy-efficient computers, says Takaaki Dohi, a spintronics researcher at the University of Tohuku who led the development of the new materials.
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