Magnetic Vortex Dynamics Driven by DC Spin-Polarized Current

We fabricated nanopillar spin-valves with a thick magnetic layer that facilitates the nucleation of a vortex. In the presence of a spin-polarized current, we observe persistent microwave oscillations, which correspond to precession of a magnetic vortex core in the thick magnetic layer, coupled to oscillations of the thinner layer, as indicated by micromagnetic simulations. The frequency varies weakly with the applied field strength and direct current (DC) current amplitude and have also been observed in near-zero applied magnetic field. These self-oscillations exhibit frequency to linewidth ratios of up to ~4000 and linewidths down to ~280 kHz at room temperature.