Deformation and motion of skyrmion bags driven by surface acoustic wave

Skyrmion bags are stable spin textured topologies with arbitrary topological charges, and have the potential to become new carriers in racetrack memory. After the discovery of skyrmion bags, the injection and driving methods of a single skyrmion are gradually applied to the manipulation of skyrmion bags. However, traditional methods, including spin current, magnetic anisotropic gradient, and spin waves generated by microwave fields, inevitably bring problems of high energy consumption and difficulty in miniaturization. With the development of strain electronics, acoustic waves have been widely used to manipulate magnetic topologies. Here, we numerically investigate the dynamical characteristic of skyrmion bags driven by surface acoustic waves. The results show that material damping and acoustic wave amplitude and frequency have a great influence on the skyrmion bag. With decrease in damping, the skyrmion bags move gradually faster. Also, increase in amplitude or frequency can generate similar effect on the velocity of skyrmion bags. Unlike acoustic wave-driven single skyrmions, the strong magnetoelastic coupling effect in the ferromagnetic film and the rich spin texture of skyrmion bags induce deformation in the skyrmion, along with a 38% increase in its velocity. Further, the deformation of the skyrmion is a combined effect of in situ rotation and breath caused by surface acoustic waves. This work demonstrates that the surface acoustic wave can be used to drive skyrmion bags, which offers potential applications for diverse storage of information based on the skyrmion bags in the future.