Perturbative approach to non-autonomous dynamics of a nonlinear spin-torque nano-oscillator

We propose a perturbative analytic approach to the description of non-autonomous dynamics of spin-torque nano-oscillators (STNO) which is based on using the autonomous (unperturbed) STNO dynamics obtained either analytically or numerically as a zero approximation. The role of a small parameter is played by the ratio of the energy of the STNO interaction with an external perturbation to the energy of the autonomous (unperturbed) STNO motion. The proposed approach is applied to a STNO based on a current-driven magnetic nano-pillar with two magnetic layers coupled by dipole-dipole interaction and spin-torque.