A Novel Device Geometry for Vortex Random Access Memories

The vortex state is one of the equilibrium configurations of soft magnetic materials and occurs in thin ferromagnetic square and disk-shaped elements of sub-micrometer size. The vortex state has a specific excitation mode: the in-plane gyration of the vortex structure about its equilibrium position. This mode can be electrically excited by a spin-polarized current. When the gyrating vortex reaches a critical velocity, a switching of the vortex core can occur. We show here how to increase the vortex velocity to reduce the switching current. The vortex core can be switched back by reversing the current direction.