Equilibria and precession in a uniaxial antiferromagnet driven by the spin Hall effect

We systematically study the stationary and precessional states in a uniaxial antiferromagnet under the dampinglike spin-orbit torque (SOT). The stable regions for all equilibria are defined by the linear stability analysis. In the regions without any stable equilibrium, we confirm that a stable conical precession may exist. Invoking symmetry arguments, we rigorously reduce the coupled Landau-Lifshitz-Gilbert equations to a single-vector one, which allows us to derive the analytic expressions of the lower and upper thresholds, the frequency, and the amplitude of precession for a weak uniaxial anisotropy. Its frequency is of the order of THz and increases almost linearly with the current. Further analysis reveals that the precession is mainly propelled by the exchange interaction in the promise that the SOT balances the damping one in average. Moreover, the investigation uncovers that a weak anisotropy can improve the frequency tunability, and a small damping benefits lowering the exciting current. Finally, the analytic expressions are verified by comparing with numerical simulations of the original Landau-Lifshitz-Gilbert equations.