Ferromagnetic van der Waals Crystal VI₃

We report structural properties, physical properties, and the electronic structure of van der Waals (vdW) crystal VI₃. Detailed analysis reveals that VI₃ exhibits a structural transition from monoclinic C2/m to rhombohedral R3̅ at T_s ≈ 79 K, similar to CrX₃ (X = Cl, Br, I). Below T_s, a long-range ferromagnetic (FM) transition emerges at T_c ≈ 50 K. The local moment of V in VI₃ is close to the high-spin state V³⁺ ion (S = 1). Theoretical calculations suggest that VI₃ may be a Mott insulator with a band gap of about 0.90 eV. In addition, VI₃ has a relatively small interlayer binding energy and can be exfoliated easily down to a few layers experimentally. Therefore, VI₃ is a candidate for two-dimensional FM semiconductors. It also provides a novel platform to explore 2D magnetism and vdW heterostructures in S = 1 system.