We present comprehensive measurements of the structural, magnetic, and electronic properties of layered van der Waals ferromagnet ${\mathrm{VI}}_3$ down to low temperatures. Despite belonging to a well-studied family of transition-metal trihalides, this material has received very little attention. We outline, from high-resolution powder x-ray diffraction measurements, a corrected room-temperature crystal structure to that previously proposed and uncover a structural transition at 79 K, also seen in the heat capacity. Magnetization measurements confirm ${\mathrm{VI}}_3$ to be a hard ferromagnet (9.1 kOe coercive field at 2 K) with a high degree of anisotropy, and the pressure dependence of the magnetic properties provide evidence for the two-dimensional nature of the magnetic order. Optical and electrical transport measurements show this material to be an insulator with an optical band gap of 0.67 eV—the previous theoretical predictions of $d$-band metallicity then lead us to believe ${\mathrm{VI}}_3$ to be a correlated Mott insulator. Our latest band-structure calculations support this picture and show good agreement with the experimental data. We suggest ${\mathrm{VI}}_3$ to host great potential in the thriving field of low-dimensional magnetism and functional materials, together with opportunities to study and make use of low-dimensional Mott physics.

• Received 13 November 2018
• Revised 28 November 2018

DOI:https://doi.org/10.1103/PhysRevB.99.041402