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Néel Spin-Orbit Torque Driven Antiferromagnetic Resonance in Mn2Au Probed by Time-Domain THz Spectroscopy

We observe the excitation of collective modes in the terahertz (THz) range driven by the recently discovered N´eel spin-orbit torques (NSOTs) in the metallic antiferromagnet Mn2Au. Temperaturedependent THz spectroscopy reveals a strong absorption mode centered near 1 THz, which upon heating from 4 to 450 K softens and loses intensity. A comparison with the estimated eigenmode frequencies implies that the observed mode is an in-plane antiferromagnetic resonance (AFMR). The AFMRabsorption strength exceeds those found in antiferromagnetic insulators, driven by the magnetic field of the THz radiation, by 3 orders of magnitude. Based on this and the agreement with our theory modeling, we infer that the driving mechanism for the observed mode is the current-induced NSOT. Here the electric field component of the THz pulse drives an ac current in the metal, which subsequently drives the AFMR. This electric manipulation of the N´eel order parameter at high frequencies makes Mn2Au a prime candidate for antiferromagnetic ultrafast memory applications.

THz spectroscopy, antiferromagnetic resonance, spin-orbit torque

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