Pivotal role of magnetic ordering and strain in lattice thermal conductivity of chromium-trihalide monolayers

TL;DR

This study reveals that spin-phonon coupling significantly influences lattice thermal conductivity in CrX3 monolayers, with magnetic phase and strain conditions causing notable variations, which could inform thermal spin device design.

Contribution

It demonstrates the critical role of spin-phonon coupling and strain in controlling thermal conductivity in 2D magnetic materials, a novel insight for material engineering.

Findings

Large spin-phonon coupling in CrX3 monolayers affects phonon dispersions.

Thermal conductivity varies significantly between ferromagnetic and paramagnetic phases.

Strain causes opposite effects on thermal conductivity depending on magnetic phase.

Abstract

Understanding the coupling between spin and phonons is critical for controlling the lattice thermal conductivity ($\kappa_l$) in magnetic materials, as we demonstrate here for CrX$_3$ (X = Br and I) monolayers. We show that these compounds exhibit large spin-phonon coupling (SPC), dominated by out-of-plane vibrations of Cr atoms, resulting in significantly different phonon dispersions in ferromagnetic (FM) and paramagnetic (PM) phases. Lattice thermal conductivity calculations provide additional evidence for strong SPC, where particularly large $\kappa_l$ is found for the FM phase. Most strikingly, PM and FM phases exhibit radically different behavior with tensile strain, where $\kappa_l$ increases with strain for the PM phase, and strongly decreases for the FM phase -- as we explain through analysis of phonon lifetimes and scattering rates. Taken all together, we uncover the very high significance of SPC on the phonon transport in CrX$_3$ monolayers, a result extendable to other 2D magnetic materials, that will be useful in further design of thermal spin devices.