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The application of radio-frequency (rf) currents in spin-torque devices allows control of magnetization reversal through frequency of the rf current. Using this effect, the impact of the rf currents on switching fields of nanostructured metallic spin valves has been investigated. The rf current injection was observed to change the critical field for free-layer magnetization reversal when the intrinsic spin-transfer-induced dynamics are frequency locked with the injected rf. Experimental results are presented by mapping the switching contour plot, and are compared with simulations in the context of macrospin models of spin transfer in metallic-spin-valve structures. Differences between this effect and the effect of rf currents on direct-current-induced magnetization reversal are highlighted by considering the role of a magnetization dispersion in the two sweep methods, which allows insights for device applications assisted by rf currents.

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