Control of vortex circulation in bistable ultra-small ferromagnetic nanodisk

The circulation reversal of magnetic vortex in ultra-small (sub-100 nm) ferromagnetic nanodots with a small off-centered hole is investigated. At zero applied field, the vortex state and the quasi uniform state are bi-stable in nanodisks. The existence of the small hole, which diameter is around the dimension of a vortex core, makes the vortex state in sub-100 nm magnetic nanomagnets is energetically more stable than uniform state. The results indicate perfect controllability of the circulation reversal using the in-plane magnetic field. We also reveal that the mechanism of the circulation reversal in sub-100 nm nanodisk is different from that in larger disk (a few hundreds nanometer to micrometer). It is paramount to control and manipulate the magnetic elements of dimension below 100 nm for their integration into nanoscopic spintronic and magnonic devices.