Owing to the spin Hall effect, an electric current flowing in a nonmagnetic conductor with a strong spin-orbit coupling creates a torque acting on spins in an adjacent ferromagnet or antiferromagnet. Such a spin-orbit torque provides the remarkable opportunity to generate steady-state auto-oscillations of spins in the magnetic nanolayer by a direct electric current. The frequency of the current-induced precession of spins in ferromagnetic spin Hall nano-oscillators (SHNOs) is well below 100 GHz, but it should increase up to the terahertz range in antiferromagnetic SHNOs. Further, in magnetoelastic antiferromagnets such as $\mathrm{Ni}\mathrm{O}$, spin oscillations should be accompanied by elastic vibrations. Here we describe the coupled magnetic and acoustic dynamics in $\mathrm{Ni}\mathrm{O}$-based SHNOs with the aid of micromagnetoelastic simulations. It is shown that the Néel-vector auto-oscillations excite high-frequency elastic vibrations inside the SHNO. Moreover, these vibrations may generate monochromatic terahertz elastic waves in the underlying nonmagnetic substrate. The frequency of the electrically excited longitudinal and transverse acoustic waves is 2 times higher than the frequency of spin oscillations, and their wave numbers comply with respective elastic dispersions. Our findings demonstrate that SHNOs comprising magnetoelastic antiferromagnets represent nanoscale sources of monochromatic coherent phonons with an electrically tunable frequency and wave number.

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• Elastic waves
• Spin Hall effect
• Spin dynamics
• Spintronics
• Antiferromagnets
• Spin torque nano-oscillators
• Micromagnetic modeling
• Terahertz sources