Skyrmions are topological spin textures with quasiparticle-like properties that may make them useful in advanced computing architectures. In this work, we studied the dynamics of magnetic skyrmions using micromagnetic simulations. We observe novel rotational and orbital motion of skyrmions when a time-varying out-of-plane magnetic field is applied to skyrmions in confined systems and excites their breathing modes. This phenomenon can be explained by the asymmetric redistribution of topological charge as skyrmions expand and contract in a confined environment. An example of this behavior can be seen below. As skyrmions expand from application of an out-of-plane field, they begin moving around the center of the system. Decreasing the magnetic field causes the skyrmions to shrink but maintain their individual rotation. Increasing the magnetic field again causes the cycle to repeat. This motion illustrates how the topological properties and the spontaneous emergence of chirality in skyrmions can result in unexpected complex behavior. Furthermore, it may have practical relevance to applications of skyrmions to neuromorphic and reservoir computing, where information may be encoded in the positions of different skyrmions. Previous groups have also observed skyrmion rotation, but have explained this with the presence of a thermal gradient.¹ Our work demonstrates a similar rotation but without having to introduce disorder into the system, possibly making the system more realizable in a practical setting.
This material is based upon work supported by the National Science Foundation under Grant No. 1922758.
References
1. Mochizuki, M. et al. Nature Materials. Vol 13., p. 241–246 (2014).

Fig. 1: Snapshots of different magnetic configurations of two skyrmions in a confined disc structure upon excitation with time varying out-of-plane fields.