Phonon and magnon dynamics across antiferromagnetic transition in 2D layered van der Waals material CrSBr

TL;DR

This study investigates how phonon and magnon excitations in the 2D van der Waals magnet CrSBr change with temperature, revealing anisotropic vibrational behavior, phonon splitting at the magnetic transition, and magnon modes.

Contribution

It provides the first detailed temperature-dependent infrared spectroscopic analysis of phonon and magnon dynamics in CrSBr, highlighting anisotropic vibrational responses and magnetic excitations across the antiferromagnetic transition.

Findings

Phonon modes along the a-axis harden with cooling.

Phonon splitting occurs at the antiferromagnetic transition.

Magnon excitation identified at ~360 cm$^{-1}$.

Abstract

We report temperature-dependent reflectivity spectra of the layered van der Waals magnet CrSBr in the far-infrared region. Polarization-dependent measurements resolve the vibrational modes along the E$\|a$- and $b$-axes and reveal the clear structural anisotropy. While the $a$-axis phonons notably harden on cooling, the $b$-axis phonon frequencies are almost temperature-independent. A phonon splitting due to the antiferromagnetic phase transition is observed for the 180~cm$^{-1}$ $a$-axis vibrational mode, accompanied by a phonon softening below $T_N$. Furthermore, an additional mode with strong magnetic characteristics at $\sim$360~cm$^{-1}$ is identified and attributed to the magnon excitation of CrSBr.