Dynamics of nano-magnetic oscillators

Abstract

We explore how non-equilibrium noise affects spin-torque switching elements and oscillators. To do so we first discuss the deterministic dynamics of magnetic tunnel junctions, introducing a convenient set of slow and fast degrees of freedom. We then derive effective Langevin equation for the slowly varying energy of precessional orbit and introduce the corresponding energy noise and energy diffusion coefficient. This allows for the formulation of a Fokker-Planck equation for the energy density distribution. We use it to analyse switching time distribution as well as the shape of the optimal spin-current pulse, which minimizes Joule losses of a switch. Finally we derive a generic expression for the linewidth of a spin-torque oscillator and discuss its dependence on temperature, spin-current amplitude and other parameters.