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Hopping Nature of Magnetic Skyrmion Motion
Mujin You,Moojune Song,Seungmo Yang,Tae-Seong Ju,Min Gyu Albert Park,Kyoung-Whan Kim,Kab-Jin Kim 한국자기학회 2021 한국자기학회 학술연구발표회 논문개요집 Vol.31 No.2
It is essential to study the dynamics of magnetic solitons such as domain walls (DWs), vertical Bloch lines (VBLs), and vortices for understanding physical features of emergent excitation. Skyrmion, a topologically protected magnetic soliton, drew a lot of attention because of its nanoscale size, low current controllability, and topological stability, which makes it an attractive candidate for technological applications, such as magnetic memory and logic devices. However, due to the complicated energy landscape and stochastic thermal motion, analyzing the current-induced dynamics of a skyrmion in the actual world is difficult, necessitating statistical treatment. Using magneto-optical Kerr effect (MOKE) microscopy and a blob-tracking method, we discover the current-induced hopping motion of skyrmions in the W/CoFeB/Ta/MgO ferromagnetic thin film. Skyrmions follow a different scaling behavior compared with magnetic DWs, which follow the conventional creep scaling law in the 2D regime. We show that skyrmions display a stochastic particle-like hopping motion, as evidenced by the stop-start characteristics of skyrmion motion at low current density (7.0 × 10<SUP>7</SUP> ~ 1.6 × 10<SUP>9</SUP> A/m²), thermal diffusion, and forward-and-backward movement. Collective segment theory with the bottleneck process shows that skyrmions exhibit hopping-like scaling behavior because of geometric constraints coming from the closed boundaries. Our study on the rigid-particle model further verifies the hopping nature of skyrmions. Our findings provide fundamental and physical insights into the stochastic motion of particles in the weakly-driven regime, which will be useful to many pioneers in the field.