High-temperature magnetostructural transition in van der Waals-layered a-MoCl3

TL;DR

This study investigates the high-temperature structural and magnetic phase transition in a-MoCl3, revealing a dimer-breaking transition near 585 K and associated changes in magnetic behavior and lattice structure.

Contribution

It provides detailed experimental and theoretical insights into the magnetostructural transition in a-MoCl3, highlighting the dimerization instability and magnetic evolution at high temperatures.

Findings

Structural phase transition at ~585 K with Mo-Mo dimer breaking

Increase in magnetic susceptibility above transition indicating local moments

Presence of two-dimensional antiferromagnetic correlations at high temperatures

Abstract

The crystallographic and magnetic properties of the cleavable 4d3 transition metal compound a-MoCl3 are reported, with a focus on the behavior above room temperature. Crystals were grown by chemical vapor transport and characterized using temperature dependent x-ray diffraction, Raman spectroscopy, and magnetization measurements. A structural phase transition occurs near 585 K, at which the Mo-Mo dimers present at room temperature are broken. A nearly regular honeycomb net of Mo is observed above the transition, and an optical phonon associated with the dimerization instability is identified in the Raman data and in first-principles calculations. The crystals are diamagnetic at room temperature in the dimerized state, and the magnetic susceptibility increases sharply at the structural transition. Moderately strong paramagnetism in the high-temperature structure indicates the presence of local moments on Mo. This is consistent with results of spin-polarized density functional theory calculations using the low- and high-temperature structures. Above the magnetostructural phase transition the magnetic susceptibility continues to increase gradually up to the maximum measurement temperature of 780 K, with a temperature dependence that suggests two-dimensional antiferromagnetic correlations.