Engineering skyrmions and emergent monopoles in topological spin crystals
Yukako Fujishiro, Naoya Kanazawa, Yoshinori Tokura
Abstract
Spin structures with a non-trivial topology can emerge through the complex interplay of underlying magnetic interactions. Representative examples are magnetic skyrmions and hedgehogs observed in various materials. Although the most typical size of a skyrmion is 10–100 nm, there has been remarkable progress in the discovery of ultra-small (<3 nm) skyrmions and hedgehogs in the last few years. The dense topological spin crystals not only hold promise for technological applications but also provide a good arena to explore gigantic responses from emergent electromagnetic fields or Berry curvature. Here, we review design principles as well as electronic functions of versatile topological spin crystals, highlighting the distinct properties between skyrmion- and hedgehog-lattice states. Among them, unconventional outcomes from hedgehog-lattice states, such as their formation mechanisms and transport properties induced by the emergent magnetic monopoles, are discussed. The manipulation of such topological spin crystals, based on the strong couplings between topology and spin-charge-lattice degrees of freedom, may pave the way for electronics emerging in the near future.