Field dependence of spin-transfer-induced vortex dynamics in the nonlinear regime

We derive an analytical model to describe the nonlinear vortex dynamics driven by spin-transfer torque in nanopillar systems. We consider the nonlinearity arising from the magnetostatic and Oersted Zeeman energies. In addition, we determine the linear and nonlinear damping forces through the calculation of the energy dissipation function. Finally, we also consider how the nonlinear dynamics changes with a perpendicular magnetic field that deforms the vortex magnetization profile. The comparison between the analytical model and numerical results obtained from micromagnetic simulations shows an excellent agreement for the change of frequency and amplitude of oscillation of the vortex as a function of the applied current and external perpendicularmagnetic field.