Unidirectional switching of magnetic vortex core confined in a cylindrical nanocavity

Ultrafast unidirectional reversal of magnetic vortex core confined in a cylindrical nanocavity is numerically investigated using micromagnetic simulations for the permalloy nanodisk. The excited modes (convergence/divergence) of the core motion are modulated differently by the cavity, depending on the dimension of the cavity, which is the main reason for the unidirectional vortex polarization switching. Assisted with the cavity, the core can be reversed well below 200 ps with less than 10 mT external magnetic field and over a wide range of field frequency. In particular, the core can be selectively switched by varying the dimension of the cylindrical cavity.