Strong and selective magnon-phonon coupling in van der Waals antiferromagnet CoPS$_3$

TL;DR

This study investigates the hybrid magnon-phonon excitations in CoPS$_3$, revealing strong, selective coupling that explains phonon mode splitting and providing refined magnetic parameters for this van der Waals antiferromagnet.

Contribution

It identifies and characterizes magnon-phonon hybrid modes in CoPS$_3$, offering new insights into their energies, coupling strengths, and magnetic parameters in this biaxial antiferromagnet.

Findings

Identification of hybrid magnon-phonon excitations in CoPS$_3$

Quantification of coupling strengths and mode splitting

Refined magnetic exchange and anisotropy parameters

Abstract

The Raman scattering response of the biaxial antiferromagnet CoPS$_3$ has been investigated as a function of both magnetic field and temperature. The peaks observed in the low-frequency spectral range (90--200~cm$^{-1}$) have been identified as hybrid magnon--phonon excitations. The energies of the bare magnon and phonon modes, as well as the effective coupling strengths between different excitation pairs, have been determined. The strong and selective magnon--phonon interaction largely accounts for the pronounced splitting of two phonon-like modes observed at 152~cm$^{-1}$ and 158~cm$^{-1}$ in the antiferromagnetic phase of CoPS$_3$. Based on the identification of bare magnon excitations and their magnetic-field dependence, we propose an updated set of parameters for the effective exchange ($J_{\mathrm{eff}} = 9.9$~meV) and biaxial magnetic anisotropy ($D = 4.3$~meV and $E = -0.7$~meV) and advocate for an apparent anisotropic $g$-factor ($g_x = g_y = 2$, $g_z = 4$) in the CoPS$_3$ antiferromagnet.