Magnon-Phonon Coupling in Layered Antiferromagnet

TL;DR

This paper develops an analytical model of magnon-phonon hybridization in layered antiferromagnets, specifically FePS3, revealing anti-crossing phenomena and providing insights into spin-phonon interactions in 2D magnetic materials.

Contribution

It introduces a simple analytical model capturing magnon-phonon coupling in 2D antiferromagnets, supported by experimental magneto-Raman spectroscopy data.

Findings

Identification of magnon and phonon modes in FePS3

Observation of anti-crossing indicating hybridization

Model predicts avoided crossings in energy spectra

Abstract

We present a fully analytical model of hybridization between magnon, and phonons observed experimentally in magneto-Raman scattering in van der Waals (vdW) antiferromagnets (AFM). Here, the representative material, FePS3, has been shown to be a quasi-two-dimensional-Ising antiferromagnet, with additional features of spin-phonon coupling in the Raman spectra emerging below the N\'eel temperature (TN) of approximately 120 K. Using magneto-Raman spectroscopy as an optical probe of magnetic structure, we show that one of these Raman-active modes in the magnetically ordered state is a magnon with a frequency of 3.7 THz (~ 122 cm-1). In addition, one magnon band and three phonon bands are coupled via the magneto-elastic coupling evidenced by anti-crossing in the complete spectra. We consider a simple model involving only in-plane nearest neighbor exchange couplings (designed to give rise to a similar magnetic structure) and perpendicular anisotropy in presence of an out-of-plane magnetic field. Exact diagonalization of the Hamiltonian leads to energy bands which show that the interaction term gives rise to avoided crossings between the hybridized magnon and phonon branches. Realizing magnon-phonon coupling in two-dimensional (2D) AFMs is important for the verification of the theoretical predictions on exotic quantum transport phenomena like spin-caloritronics, topological magnonics, etc.