Magnetic skyrmions are twists in the magnetization of a material that possess particle-like properties. They are localized in space, can be moved around, interact with one another, form crystals, and undergo skyrmion-antiskyrmion pair-production and annihilation. They are stabilized by their special topology, which leads to rich underlying physics, such as Magnus force dynamics and an emergent electrodynamics based on Berry phases. More practically, their small size, topological stability, and expected ease of movement in response to spin torques that use little energy has provoked a rapid expansion in interest due to their potential for applications in information storage and processing hardware.

The mathematical concept of a topologically stable quasiparticle as a solution to a non-linear field equation was proposed in the 1950s by Skyrme to explain the stability of hadrons in quantum field theory. Whilst never becoming part of the mainstream of particle physics, the concept has an inherent interdisciplinarity and has proved useful in various areas of condensed matter and materials physics such as the quantum Hall effect, liquid crystals, and now magnetism. Magnetic skyrmions were first discovered in 2009 in the low-temperature helimagnet MnSi. In the past few years, new materials bearing skyrmions at room temperature have been discovered, in the form both of bulk crystals (CoMnZn) and multilayers such as Pt/Co/Ir. The latter are in thin film form, and hence are suitable for integration into microelectronics manufacturing. Nevertheless, questions remain about skyrmions’ fast dynamics, whether their motion, nucleation, and annihilation can be controlled rather than being stochastic, and the possibilities presented by the coupling of skyrmions to other degrees of freedom in hybrid nanostructures. It seems unlikely that this handful of just-discovered room-temperature materials are the optimal ones, and rational design of novel materials exhibiting tailored properties for different applications is an important outstanding problem. It is also the case that skyrmions represent just the first member of a family of topological objects, such as antiskyrmions, bimerons, and hopfions. The properties and promise of these objects remain largely unexplored territory, but the first realizations of some of these in real materials have taken place in the last one-two years.

electronic material electronic structure ferroelectricity ferromagnetic Hall effect magnetic properties magnetoresistance (transport) semiconducting spintronic