Magnetic skyrmions are twists in the magnetisation of a material that possess particle-like properties. They are localised in space, can be moved around, interact with one another, crystallise into lattices, and undergo skyrmion-antiskyrmion pair-production and annihilation. They are stabilised 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 different 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 year or two, new materials bearing skyrmions at room temperature have been discovered, in the form both of bulk crystals (CoMnZn) and magnetic multilayers such as Pt/Co/Ir. The latter are in thin film form, and hence are suitable for integration into microelectronics manufacturing processes. Nevertheless, questions remain about skyrmions’ fast dynamics, whether their motion, nucleation, and, annihilation can be controlled rather than stochastic, and the possibilities presented by the coupling of skyrmions to other degrees of freedom in hybrid structures. It seems unlikely that this handful of just-discovered room-temperature materials are the optimal ones, and rational design of new 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 anti-skyrmions, chiral bobbers, merons, and biskyrmions. The properties and promise of these objects remains largely unexplored territory, but the first examples of the realisation of some of these in real materials has taken place in the last one or two years.

Therefore the time is right for another symposium to follow up the successful one held at the MRS Fall Meeting 2016. The field moves forward ever more quickly, and substantial progress is expected in the two year interval between the two symposia. The number of active groups is increasing rapidly in the US, Europe, and Asia, as is the number of publications in the most prestigious journals. It is not clear as yet what materials will deliver the best performance, with new ones being discovered all the time. The effects of the disorder that is inevitable in the thin film systems that are required for viable technologies needs to be understood and brought under control. It is also an open question as to what device designs will yield new functionalities: there are several proposals for information storage/processing devices that need to be realised experimentally and tested, for which optimal materials must be sought.

The symposium is expected to attract attendees interested in the condensed matter physics of these topologically non-trivial magnetic quasiparticles from both theoretical and experimental viewpoints, as well as materials scientists working on the design and synthesis of new materials, electronic engineers with an interest in spintronic device and systems architectures that can exploit skyrmions, and computer scientists who concern themselves with non-Boolean/neuromorphic information processing schemes using such devices.

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