The crystallographic and magnetic properties of the cleavable 4d3 transition metal compound α−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.
Michael McGuire, Jiaqiang Yan, Paula Lampen-Kelley, Andrew May, Valentino Cooper, Lucas Lindsay, Alexander Puretzky, Liangbo Liang, Santosh KC, Ercan Cakmak, Stuart Calder, and Brian Sales. "High temperature magneto-structural transition in van der Waals-layered -MoCl3" Physical Review Materials (2017). doi:10.1103/PhysRevMaterials.1.064001