Ultra-low critical velocity switching of magnetic vortex core polarity*

Topological structures in magnetism are subject of great interest both from physics and technological perspectives. For instance, the topology of a magnetic vortex results in an extremely stable magnetic vortex core polarity, which makes vortices attractive for applications such as information storage. Switching of the magnetic vortex core polarity, as a result of this high stability, is typically achieved either with large magnetic fields or strong dynamic driving. Here, we show that the interaction of the magnetic vortex core with localized defects results in the reduction of the strong stability by more than an order of magnitude. We excite vortex dynamics in thin Permalloy disks, and track the magnetic vortex core orbits using 3D time-resolved Kerr microscopy. In pristine samples with weak defects, we observe normal gyrations of the vortex core. After laser-induced generation of strong defects, however, we observe repeated vortex core reversal at much-reduced driving strength. Micromagnetic simulations reveal how local reduction of exchange coupling can create vortex core reversal sites for deterministic vortex core switching at ultra-low critical velocities.