Periodic polarity switching of a pinned vortex core in nanodisks: subharmonic control via geometric confinement

Abstract We demonstrate fast, reversible, and fully periodic polarity switching of vortex core pinned at a central nanohole in Permalloy and CoFe nanodisks. An oscillating current drives the core out of the defect in a zero-polarity state. Once expelled, the core acquires a finite polarity and performs a confined gyrotropic motion while remaining attracted to the hole. It is subsequently reabsorbed and reemerges with opposite polarity. The switching frequency is not arbitrary but locked to rational fractions of the drive, establishing robust subharmonic phase-locking of the vortex polarity. This defect-assisted mechanism is reproducible across materials and excitation conditions. Because the polarity oscillation is phase-locked to the external drive, the final state can be deterministically selected through timing control, offering a scalable pathway for topological state manipulation. Our findings highlight engineered core dynamics as a promising strategy for spintronic applications.