Fast, low-power defect-induced polarity switching of a magnetic vortex core

The core polarity of a topologically-protected magnetic vortex state is predicted to be extremely stable, and as such is considered as a candidate for non-volatile memory storage. However, here we show that the vortex core (VC) polarity is susceptible to rapid, repeatable switching even under low-amplitude motion. We excite vortices in thin permalloy disks with a magnetic field pulse, and observe the dynamic response using 3D time-resolved Kerr microscopy. In as-fabricated samples, we observe typical gyrations of the VC as it relaxes back to equilibrium. However, we observe a radically altered VC trajectory as prolonged pulsed laser exposure begins to change the VC pinning behavior near the disk center. In this region, the sense of gyration switches multiple times over tens of nanoseconds, indicating highly deterministic switches of the VC polarity that remain clear over >10⁶ averaged repetitions. By translating the VC equilibrium position, we can tune the number of switches to zero, or obtain single deterministic switches using field pulses of less than 0.5 mT amplitude and 3 ns duration. Finally, we show simulation results of VC-defect interaction that shed light on this phenomenon.