Precise transport of skyrmions by surface acoustic waves*

Skyrmions are topologically protected chiral spin structures showing great potential for the next generation of data storage and processing devices^[1]. However, controlling such chiral spin textures efficiently and precisely remains unsolved. Here, we demonstrate the precise transport of skyrmions by surface acoustic waves using micromagnetic simulations (Mumax3) ^[2]. The skyrmion was initialised at different positions along the nanotrack. Results showed that with the application of the standing SAW, the skyrmion did not move if its initial position was at the antinodes of the standing SAW. Whereas starting from a node, the skyrmion did move towards the closest anti-node of the standing SAW indicating that the strain gradient is the origin of the SAW-driven skyrmion motion^[3]. The skyrmion moves continuously in the presence of the travelling SAW regardless of its initial position with a higher velocity (2.39 cm/s) than that of the standing SAW-induced skyrmion motion. This is due to the travelling SAWs providing a constant driving force to the skyrmion. The skyrmion also moves in the vertical direction owing to its chirality. Orthogonal SAWs (horizontal travelling SAW and transverse standing SAW) were then applied to the skyrmion, which can drive skyrmion horizontal motion and pin the skyrmion in the desired trajectory. Results showed that in the presence of orthogonal SAWs, the skyrmion moved along the centre of the nano-track with very limited vertical motion.