Parametric instability of a magnetic junction under modulated spin-polarized current

The stability is analyzed of the magnetic junction collinear configurations against small fluctuations under amplitude-modulated current with current-perpendicular-to-plane mode. High spin injection is assumed. Under parametric resonance conditions, with the modulation frequency twice the precession frequency, instability is possible of one, or another, or both the collinear configurations. When the direct component of the current density exceeds the instability threshold of the antiparallel configuration, the parametric instability is suppressed by nonparametric one which is induced by the direct current. The parametric instability manifests itself as lowering the threshold of the direct current density in the presence of the high-frequency current; such an effect has been observed in experiments repeatedly.