Effects of radio-frequency current on spin-transfer-torque-induced dynamics

In this work we investigate the highly unexplored PS dynamical regime as well as the effects of additional rf currents on the PS and switching modes. The PS modes are found to interact with the applied rf currents having frequencies in the range of the dc-only driven modes, and under certain conditions are found to frequency lock. In contrast to previous frequency locking results [7, 8, 9], by looking at these effects in the PS regime, we find a measurable dependence of the dc switching threshold on the external rf frequency, finj. In the locking range the rf appears to have a stabilizing effect which hinders switching, however, at frequencies just below this range, we find a measurable reduction in the direct critical current for switching, Ic. While we have already reported this effect [10], an explanation for the origin of this effect has not been given. In this work, by studying the behavior of this system in frequency domain and through macrospin simulations (MS) (using the Landau-Lifshitz-Gilbert equation with Slonczewski STT [2]) we provide a description of the magnetization dynamics originating from the interaction between the dc driven switching modes and the applied rf. The results show good agreement with our experimental data. EXPERIMENT