Tunable range of terahertz oscillations triggered by the spin Hall effect in a biaxial antiferromagnet

We present a theoretical study on the current and frequency windows of self-oscillations induced by the dampinglike spin-orbit torque in a biaxial antiferromagnet. By the linear stability analysis and averaging technique, we analytically formulate the lower and upper thresholds and the frequency of self-oscillations. We find that the self-oscillation range is highly sensitive to the damping and magnetic anisotropies, which have a variety of options in abundant antiferromagnets. Beyond a critical damping, the self-oscillation can arise after the instability of an antiferromagnetic state, with its range widening for a heavier damping. Below it, a spin-flip transition occurs when increasing the current, similar to the spin flip under an increasing magnetic field. Meanwhile, we examine the role of anisotropies. With the spin polarization along the easy axis, the weak easy- and hard-axis anisotropies allow self-oscillations, the range of which is broadened for weaker anisotropies. At the same time, the spin-flip transition is permitted for strong anisotropies. If the spin polarization coincides with the hard axis, the transition types are mainly determined by the easy-axis anisotropy. For a weak easy-axis anisotropy, the self-oscillation can develop with its range expanding for a stronger hard-axis anisotropy. Finally, we envision that (tunneling) anisotropic magnetoresistance may act as an effective means to probe the oscillations.