Terahertz spin dynamics in antiferromagnetic Mn₂Au

In antiferromagnets, the intrinsic terahertz (THz) magnon resonances are expected to enable pathways to high-speed spin information processing. In antiferromagnetic CuMnAs and Mn₂Au, switching of the Néel vector has been demonstrated by using pulsed electrical currents and free-space THz pulses [1-3]. The switching was attributed to the Néel spin-orbit torque (NSOT), which is proportional to the current. However, the underlying spin dynamics have not yet been studied on their natural, i.e. sub-picosecond, time scales.
Here, we employ a THz-pump optical-probe setup to investigate spin dynamics in Mn₂Au thin films in the small-perturbation regime. The direction of the average Néel vector was prealigned via a spin-flop transition in a magnetic field of 60 T [4]. We observe a signal that scales linearly with the driving THz field and whose shape, frequency and symmetry is consistent with NSOT-driven spin dynamics. The spin motion corresponds to a strongly damped magnon with frequency of 0.6 THz, suggesting that NSOT allows for spin control via ultrafast currents in Mn2Au.

[1] P. Wadley et al., Science 351, 587-590 (2016)
[2] K. Olejnik et al., Sci. Adv. 4, eaar3566 (2018)
[3] S. Yu. Bodnar et al., Nat. Comm. 9, 348 (2018)
[4] A. Sapozhnik at al., Phys. Rev. B 97, 134429 (2018)