Visualizing the dynamics of sub-100 nm Néel Skyrmions in Multilayer Nanowires*

The emergence of room temperature skyrmions in technologically-relevant multilayers has intensified efforts towards realizing these topologically stable, nanoscale spin structures for next generation technologies, in particular, neuromorphic computing, Internet of Things. Of great interest is the lateral manipulation of skyrmions on a Racetrack, which builds on their deterministic response to current-induced spin torques in nanowires. Thus far,a clear understanding of the factors governing the dynamics of small (sub-100 nm) skyrmions in granular films remains to be established. Here we utilize magnetic force microscopy to investigate the collective dynamics of a dense skyrmion array with individual speeds up to 24ms^-1, in 2um-wide Pt/Co/MgO nanowires. By examining>2x10⁴ instances of skyrmion motion, we observe several emergent behaviours including the interplay of edge confinement and skyrmion Hall effect, which is crucial to understanding edge-induced skyrmion pinning in Racetrack architectures. In this work, we also detail the effects of skyrmion size, skyrmion-skyrmion interactions and pinning on skyrmion dynamics.The rich dynamics of skyrmions uncovered in our study will potentially fast-track the realization of skyrmion-based Racetrack devices.