Spin-Torque-Driven Vortex Dynamics in Nanopillars with In-Plane or Out-of-Plane Polarizers

We studied two types of nanopillar spin-valves: one using an in-plane magnetized polarizer layer and one using a perpendicular polarizer. Both types of devices contain a magnetic vortex in the second magnetic layer. Under direct current (DC) bias, the devices with in-plane polarizer exhibit persistent microwave oscillations that are characterized by two oscillation peaks and long timescale, discrete, fluctuations that lead to linewidth broadening. Under certain bias conditions, the devices with a perpendicular polarizer show behavior that is consistent with the switching of the vortex core under the effect of spin-polarized current.