Autonomous and Non-Autonomous Dynamics of Spin Hall Auto-Oscillators

A novel type of spin-torque nano-oscillators driven by pure spin current generated via the spin Hall effect has been demonstrated recently. The study of the effects of external microwave signals on these Spin Hall oscillators (SHO) is reported. It is shown that SHO can be efficiently synchronized by applying a microwave signal at approximately twice the frequency of the auto-oscillation, which opens additional possibilities for the development of novel spintronic devices. It is found that the synchronization exhibits an apparent threshold determined by magnetic fluctuations pumped above their thermal level by the spin current, and is significantly influenced by the nonlinear self-localized nature of the auto-oscillatory mode.