Interaction of surface acoustic waves with weakly pinned magnetic skyrmions

Magnetic skyrmions, topologically protected particle-like magnetic textures, are promising for data storage and processing devices. Skyrmions in thin films can be manipulated electrically via spin-orbit torque, but this method requires a high current density, which can cause Joule heating of the material, thereby wasting energy and affecting the stability of skyrmions. What is more, skyrmions typically exhibit both longitudinal and transverse motion (the skyrmion Hall effect) in response to a spin-orbit torque, which can cause skyrmions to move off track and annihilate at device edges. This experiment will investigate the alternative and potentially more efficient and precise approach of manipulating skyrmions with surface acoustic waves (SAWs). We have developed a magnetic thin film multilayer for this purpose (Pt/CoFeB/Ru) in which a weakly pinned skyrmion liquid may be formed at low applied magnetic field. The skyrmions are typically 1 μm in diameter or smaller, requiring high spatial resolution imaging techniques. Following our previous successful measurements of the SAW effect on domain walls, now, using XMCD-PEEM, we aim to investigate: (a) whether a standing SAW reduces the nucleation field, and preferentially nucleates skyrmions at antinodes, (b) how the standing SAW interacts with the skyrmion liquid phase, and (c) whether a phase-shifted standing SAW or travelling SAW can transport skyrmions. Recent works simulate SAW-skyrmion interaction, or use SAWs to experimentally nucleate or confine their current-driven motion in multilayers with high pinning. In contrast, our experiment aims at efficient skyrmion transport purely by SAWs in a low-pinning material.