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.
@article{arxiv.1711.02708,
title = {High-temperature magnetostructural transition in van der Waals-layered a-MoCl3},
author = {Michael A. McGuire and Jiaqiang Yan and Paula Lampen-Kelley and Andrew F. May and Valentino R. Cooper and Lucas Lindsay and Alexander Puretzky and Liangbo Liang and Santosh KC and Ercan Cakmak and Stuart Calder and Brian C. Sales},
journal= {arXiv preprint arXiv:1711.02708},
year = {2017}
}