Ultrafast amplification and non-linear magneto-elastic coupling of coherent magnon modes in an antiferromagnet

TL;DR

This study reveals ultrafast magnon mode coupling in an antiferromagnet driven by non-linear magneto-elastic interactions at domain walls, with potential for optical control of spin dynamics.

Contribution

It uncovers a novel non-linear coupling mechanism between THz and GHz magnon modes mediated by domain walls in antiferromagnetic NiO.

Findings

Detection of coupling between THz and GHz magnon modes.

Modeling shows magneto-elastic interaction via domain walls causes the coupling.

Coupling can be optically controlled through exciton-magnon resonance.

Abstract

We investigate the role of domain walls in the ultrafast magnon dynamics of an antiferromagnetic NiO single crystal in a pump-probe experiment with variable pump photon energy. Analysing the amplitude of the energy-dependent photo-induced ultrafast spin dynamics, we detect a yet unreported coupling between the material's characteristic THz- and a GHz-magnon modes. We explain this unexpected coupling between two orthogonal eigenstates of the corresponding Hamiltonian by modelling the magneto-elastic interaction between spins in different domains. We find that such interaction, in the non-linear regime, couples the two different magnon modes via the domain walls and it can be optically exploited via the exciton-magnon resonance.