Thermal Hall effect in a van der Waals triangular magnet FeCl2

TL;DR

This study reports significant thermal Hall effect and magneto-thermal conductivity in the van der Waals antiferromagnet FeCl2, revealing strong magnon-phonon interactions and complex underlying mechanisms.

Contribution

It provides the first observation of thermal Hall effect in FeCl2 and explores the interplay between magnons and phonons in a van der Waals magnetic material.

Findings

Magneto-thermal conductivity exceeds 700%, indicating strong magnon-phonon coupling.

Thermal Hall signal changes sign at the spin-flip transition.

Theoretical calculations suggest Berry curvature and other mechanisms contribute to THE.

Abstract

Thermal transport is a pivotal probe for studying low-energy, charge-neutral quasi-particles in insulating magnets. In this Letter, we report an observation of large magneto-thermal conductivity and thermal Hall effect (THE) in a van der Waals antiferromagnet FeCl2. The magneto-thermal conductivity reaches over ~700%, indicating strong magnon-phonon coupling. Furthermore, we find an appreciable thermal Hall signal which changes sign concurrently with the spin-flip transition from the antiferromagnetic state to the polarized ferromagnetic state. Our theoretical calculations suggest that, in addition to the Berry curvature induced at the anticrossing points of the hybridized magnon and acoustic phonon modes of FeCl2, other mechanisms are needed to account for the magnitude of the observed THE.