Few-nm tracking of magnetic vortex core trajectories near and inside defects

Nanoscale magnetic textures such as vortices and skyrmions have attracted attention for applications in memory, logic, or microwave sources. For these applications, the effect of defects on the magnetization dynamics is critical, which can cause pinning or deviations of the trajectory as predicted by the Thiele equation. We report on the experimental observation of magnetic vortex core motion inside and near defects. We use a 3D time-resolved Kerr microscope to track the trajectory of a magnetic vortex core with spatial resolution of several nanometers and nanosecond time resolution [1]. We position the vortex core within a thin permalloy disk using a static magnetic field and excite the vortex core dynamics using a fast magnetic pulse. In a region relatively free of defects, the trajectory of the vortex core is a circular spiral path, decaying to the equilibrium position. When the moving vortex core approaches a defect that causes significant vortex pinning, however, we observe that the vortex core continues moving but deviates from its circular path in response to the defect. Sufficiently close to a large defect, we also observe enhanced damping to a new pinned equilibrium within the defect. This technique provides a method for probing the motion of nanoscale spin textures as they interact with defects in the material either leading to pinning or altered dynamics.

[1] M. Mehrnia, J. Trimble, and J. Berezovsky, Three dimensional frequency-and phase-multiplexed magnetooptical microscopy, Opt. Express 27, 33942 (2019).