Transient dynamics leading to self-oscillations in nanomagnets driven by spin-polarized currents

Magnetization dynamics in uniformly magnetized nanomagnets subject to spin-polarized currents is studied by Landau-Lifshitz-Gilbert (LLG) equation with a spin-transfer torque term. This kind of magnetic system may exhibit stationary states and self-oscillatory regimes. By using the fact that spin-transfer torque and Gilbert damping are small perturbations of the conservative LLG dynamics, the analysis of self-oscillations is carried out by an appropriate perturbation technique. Averaging technique is then used to derive an approximated model for the energy dynamics which enables one to study the transient leading to self-oscillatory regimes. The accuracy of the proposed analytical technique is tested by comparison with numerical solutions of the LLG equation.