Aggregation and collapse dynamics of skyrmions in a non-equilibrium state

Authors

Xiuzhen Yu, Daisuke Morikawa, Tomoyuki Yokouchi, Kiyou Shibata, Naoya Kanazawa, Fumitaka Kagawa, Taka-hisa Arima & Yoshinori Tokura 

Abstract

Magnetic skyrmions have attracted attention because of their emergent electromagnetic properties. In particular, non-equilibrium-state skyrmions, which are protected by topology and hence can exist over a wider temperature–magnetic-field region, show promise for possible practical applications, but their dynamics remain elusive. Here, we report the observation of a magnetic-field-induced dynamical transition from the metastable hexagonal-lattice skyrmion crystal (SkX) at a zero bias-field to an amorphous state via the densely vacancy-populated SkX. With decreasing field, on the other hand, the aggregate transforms from ‘random particles’ to ‘microcrystals’ of skyrmions in a non-equilibrium state, in analogy to colloidal crystallization, and subsequently undergoes a topologically distinct phase separation between the SkX and helical/conical domains accompanied by topological defects. These observations directly demonstrate the aggregation and collapse dynamics of metastable skyrmions and may provide a route to other nontrivial topological phenomena such as the zero-magnetic-field topological Hall effect.

Nature Physics：https://www.nature.com/articles/s41567-018-0155-3