Theory of spin-current-induced auto-oscillations in biaxial antiferromagnets

We study the dynamics of the Neel order in biaxial antiferromagnets under the influence of an antidamping-like torque exerted by a spin current. Large spin currents can produce steady-state precession in a plane perpendicular to spin polarization. When the spin-current is polarized along the hard-anisotropy axis, the Neel order revolves in the most stable `easy plane' with dynamical equation of a damped-driven pendulum. The two-dimensional parameter space of drive and damping is explored to determine the regimes of periodic and stationary solutions, and the hysteretic region is identified. Analytic solutions for oscillations in angular velocity are derived when damping and drive are large, and a model for the fundamental mode is conceived. The oscillations are coherent for large drive and spiky for large damping near the threshold. We also propose experimental setup for electrical control and detection of terahertz auto-oscillations in thin films. The in-plane antiferromagnet overlaid with lateral spin-valve structure and the perpendicular antiferromagnet overlaid with spin-Hall structure form compatible geometries. The current drive after initiating oscillations can be lowered by exploiting the hysteresis to mitigate excessive Joule heating in the metal and to tune the oscillations to detectable frequencies. Room-temperature antiferromagnetic insulators such as in-plane NiO and perpendicular Cr2O3 are considered to calculate the current density, oscillation frequency and spin-pumping voltage.