Spin-topology dependent brownian diffusion of skyrmions

Non-interacting particles exhibiting Brownian motion have been observed in many occasions of sciences, such as molecules suspended in liquids, optically trapped microbeads, and spin textures in magnetic materials. In particular, a detailed examination of Brownian motion of spin textures is important for designing thermally stable spintronic devices which motivates the present study. In this Letter, through using temporally and spatially resolved polar magneto-optic Kerr effect (MOKE) microscopy, we have experimentally observed the thermal fluctuation-induced random walk of a single isolated Neel-type magnetic skyrmion around room temperature in an interfacially asymmetric Ta/CoFeB/TaOx multilayer. More importantly, an intriguing spin-topology dependent diffusion behavior of skyrmions has been identified. The onset of Brownian dynamics of a single skyrmion induced by the random thermal noises, including a linearly temperature dependent diffusion coefficient and spin-topology dependent diffusion were further formulated based on the stochastic Thiele equation. The numerical and experimental demonstration of spin-topology dependent Brownian dynamics of skyrmions can be useful for understanding the nonequilibrium magnetization dynamics and implementing novel skyrmionic devices.