The modes of skyrmionium motion induced by vacancy defects on a racetrack

Abstract

A magnetic skyrmionium composed of two skyrmions with opposite topological charges shows the advantages of high mobility and no skyrmion Hall effect. However, the defects of practical materials are inevitable, which could influence the dynamics of the skyrmionium and even destroy its magnetic structure. Herein, we theoretically investigate the motion of the skyrmionium driven by spin waves on a racetrack with vacancy defects. Three modes of the motion (reflection, pinning, and depinning) are found by adjusting the size of defects, the amplitude and frequency of spin waves. When the defect radius Rd ≥ Rc, the skyrmionium is reflected along the direction of spin waves source and stops in front of the defect after a round-trip oscillation, ascribed to the competition between the driving force induced by spin waves and the potential well induced by defects. When the defect radius Rd < Rc, the skyrmionium can be pinned in the position of the defects, where the energy provided by spin waves is consumed by the wiggling of the skyrmionium. And the depinning of skyrmionium can be realized by increasing the driving force of spin waves, overcoming the energy barriers induced by defects. Our results provide an insight into the interaction between the skyrmionium and defects, which could be used to guide the design of the skyrmionium-based spintronic devices in practical materials.