Theory of current-induced skyrmion dynamics close to a boundary

Skyrmions are the prime candidate as the information carrier of tomorrow's data storage devices. But they face the risk of annihilation on encountering a boundary. We show how skyrmions can avoid this undesired outcome through management of their anisotropy energies. Specifically we derive an edge potential and a contact interaction term which only operate close to the edge. We verify the accuracy of these two terms by modelling a realistic skyrmion system and comparing it with micromagnetic simulations. We not only observe and explain the speeding up of skyrmions near the edge (which had been expected) but also observe and explain a peculiar asymmetry in the motion (where it speeds up more on one edge compared to the other). We devise a means to stabilize a skyrmion against Magnus force (without the need for a transverse current) by modifying the damping parameters. Finally, we note a link between these damping parameters and the anisotropy energy. Our results will be of value in the design of skyrmion-based devices and would give fresh impetus to the study of magnetic anisotropy. Significance: Skyrmions are the prime candidate as information carrier of tomorrow's ever ubiquitous data storage devices. But they face the risk of annihilation on encountering a boundary. We propose a model for the skyrmion-edge dynamics by deriving an edge potential and a contact interaction, which are incorporated into the standard Thiele equation for the current-induced motion of skyrmions. We compare this model with micromagnetic simulations which leads us to observe and explain the speeding up of skyrmions near the edge. We also observe and explain a peculiar asymmetry in the motion (where skyrmions speed up more on one edge compared to the other) and discover the important role played by the damping constants of the Thiele equation. We devised a means to stabilize a skyrmion against Magnus force (without the need for a transverse current) by modifying the damping parameters. A connection with the anisotropy energy is noted.