Deterministic Switching of the Magnetization States in Cobalt Nanorings

We studied the magnetoresistance of symmetric cobalt nanorings with nanowires attached at diametrically opposite positions. Deterministic switching, induced by an external magnetic field between the stable magnetization states, is demonstrated using histograms of the resistance changes as a function of an external magnetic field. The changes of the switching fields were studied as the lateral dimensions of these elements were varied systematically. The field required to switch between the vortex state and the onion state of the rings decreases as the line widths of the elements were increased. The vortex state is unstable at the larger line widths. Our experimental observations are explained using micromagnetic simulations.