Emission of coherent THz magnons in an antiferromagnetic insulator triggered by ultrafast spin-phonon interactions

TL;DR

This paper demonstrates the generation of both broadband incoherent and narrowband coherent THz magnons in NiO/Pt thin films through ultrafast spin-phonon interactions, revealing two distinct excitation mechanisms with potential for fast spintronic devices.

Contribution

It uncovers two excitation processes in antiferromagnetic NiO, one optical spin torque and one strain-wave-induced THz torque, enabling coherent THz magnon emission.

Findings

Demonstrated broadband incoherent and narrowband coherent THz magnons.

Identified two excitation mechanisms with distinct timescales (<50 fs and >300 fs).

Showed potential for ultrafast opto-spintronic device development.

Abstract

Antiferromagnetic materials have been proposed as new types of narrowband THz spintronic devices owing to their ultrafast spin dynamics. Manipulating coherently their spin dynamics, however, remains a key challenge that is envisioned to be accomplished by spin-orbit torques or direct optical excitations. Here, we demonstrate the combined generation of broadband THz (incoherent) magnons and narrowband (coherent) magnons at 1 THz in low damping thin films of NiO/Pt. We evidence, experimentally and through modelling, two excitation processes of magnetization dynamics in NiO, an off-resonant instantaneous optical spin torque and a strain-wave-induced THz torque induced by ultrafast Pt excitation. Both phenomena lead to the emission of a THz signal through the inverse spin Hall effect in the adjacent heavy metal layer. We unravel the characteristic timescales of the two excitation processes found to be < 50 fs and > 300 fs, respectively, and thus open new routes towards the development of fast opto-spintronic devices based on antiferromagnetic materials.