Evolution of magnetism in single crystals of the van der Waals compound $\mathrm{V}{\mathrm{I}}_3$ in external pressure up to 7.3 GPa studied by measuring magnetization and ac magnetic susceptibility is reported. Four magnetic phase transitions, at $T_1=54.5\mathrm{K}, T_2=53\mathrm{K}, T_{\mathrm{C}}=49.5\mathrm{K}$, and $T_{\mathrm{FM}}=26\mathrm{K}$, respectively, have been observed at ambient pressure. The first two have been attributed to the onset of ferromagnetism in specific crystal-surface layers. The bulk ferromagnetism is characterized by the magnetic ordering transition at Curie temperature $T_{\mathrm{C}}$ and the transition between two different ferromagnetic phases $T_{\mathrm{FM}}$, accompanied by a structure transition from monoclinic to triclinic symmetry upon cooling. The pressure effects on magnetic parameters were studied with three independent techniques. $T_{\mathrm{C}}$ was found to be almost unaffected by pressures up to 0.6 GPa whereas $T_{\mathrm{FM}}$ increases rapidly with increasing pressure and reaches $T_{\mathrm{C}}$ at a triple point at ≈ 0.85 GPa. At higher pressures, only one magnetic phase transition is observed moving to higher temperatures with increasing pressure to reach 99 K at 7.3 GPa. In contrast, the low-temperature bulk magnetization is significantly reduced by applying pressure (by more than 50% at 2.5 GPa) suggesting a possible pressure-induced reduction of vanadium magnetic moment. First-principles calculations of $\mathrm{V}{\mathrm{I}}_3$ under pressure allow us to ascribe the evolution of $T_{\mathrm{C}}$ with pressure to the reduction of interplanar distance, including the observed slope change at 0.6 GPa. These calculations also describe the associated band gap closing, showing that with a modest compression the material would become metallic. Overall, the large pressure range covered corresponds to a significant change of interplanar interactions. The obtained data thus allow us to shed light on how does the transition between the three-dimensional (3D) and quasi-2D system affect magnetic interactions in the system.

• Received 20 October 2020
• Revised 15 December 2020
• Accepted 15 January 2021

DOI:https://doi.org/10.1103/PhysRevB.103.054424