  The realization of THz sources is a fundamental aspect for a wide range of
applications. Over different approaches, compact THz oscillators can be
realized taking advantage of dynamics in antiferromagnetic (AFMs) thin films
driven by spin-Hall effect. Here we perform a systematic study of these THz
oscillators within a full micromagnetic solver based on the numerical solution
of two coupled Landau-Lifshitz-Gilbert-Slonczewski equations, for the case of
ultra-thin films, i.e. when the N\'eel temperature of an AFM is substantially
reduced. We have found two different dynamical modes depending on the strength
of the Dzyaloshinskii-Moriya interaction (DMI). At low DMI, a large amplitude
precession is excited where both the magnetizations of the sublattices are in a
uniform state and rotate in the same direction. At large enough DMI, the ground
state of the AFM becomes non-uniform and the antiferromagnetic dynamics is
characterized by ultrafast domain wall motion.
