Dynamics of Bloch point in an asymmetric patterned permalloy disk

A Bloch point is a magnetic singularity in ferromagnetic materials, where the local magnetization vanishes [1, 2]. Bloch point shows intriguing physical behaviors as a discrete spin texture - pinning and depinning at atomic lattices, and the spin-Cherenkov effect [3, 4]. Furthermore, it has been known that the Bloch point plays a critical role in the switching of 2D magnetic textures such as magnetic vortex core and skyrmions with changes of their local topological numbers [5]. However, it has been challenging to study the physical behavior of a Bloch point including its static and dynamic motion experimentally. First, it is very difficult to secure the stabilized Bloch point in ferromagnetic materials. Second, it is necessary to observe internal magnetic structures surrounding the Bloch point on nanometer scale, which requires a state-of-the-art imaging technique with high sp atial resolution. In this presentation, we report the Bloch point in the middle of vortex core structure and its dynamics directly observed by the time-resolved magnetic full-field transmission soft X-ray microscopy (MTXM) [6]. From the measurement of the Bloch-point motion and its effects on the magnetic vortex-core dynamics, we successively addressed the atomic nature of the Bloch point. We will discuss detailed structures of Bloch points according to its type and topological numbers and fundamental understandings on the role of the atomic nature of the Bloch point in magnetic textures??? dynamic motion and switching