Effect of microwave irradiation on spin-torque-driven magnetization precession in nanopillars with magnetic perpendicular anisotropy

The effect of microwave irradiation on the spin-torque-driven magnetization dynamics is studied in (Co/Ni)-based nanopillar spin valves with perpendicular magnetic anisotropy. For this purpose, a setup was developed to measure the ac as well as the dc resistance of the nanopillar under applied fields and injected polarized currents, while irradiating microwaves with varying frequency (6--18 GHz) and power. We find that the microwave irradiation amplifies and maintains the precessional state of the eigenresonance within a larger field range. The experiments are discussed in comparison to micromagnetic as well as macrospin simulations utilizing the nonlinearized Landau-Lifshitz-Gilbert equation.