Alternating spin-polarized current induces parametric resonance in spin valves

Ferromagnetic systems under the influence of spin-polarized currents exhibit rich spatiotemporal dynamics at nanoscales. We study spin-transfer nano-oscillators driven by the combination of alternating and direct spin-polarized electric currents. We show here that the alternating current induces parametric instabilities on spin valves, that is, the magnetization responses at half the forcing frequency. A spatial self-organization emerges as a result of the oscillatory current, which includes dissipative solitons and Faraday-type waves. The parametric regime is described analytically by means of the Landau-Lifshitz-Gilbert-Slonczewski equation, in good agreement with micromagnetic simulations including the full dipolar field.