Tuning the electronic and magnetic properties of NiBr2 via pressure

Transition metal dihalides (MX 2, M= transition metal, X= halide) have attracted much attention recently due to their intriguing low-dimensional magnetic properties. Particular focus has been placed in this family in the context of multiferroicity-a common occurrence in MX 2 compounds that adopt noncollinear magnetic structures. One example of helimagnetic multiferroic material in the dihalide family is represented by NiBr2. Here, we study the evolution of the electronic structure and magnetic properties of this material under pressure using firstprinciples calculations combined with Monte Carlo simulations. Our results indicate there is significant magnetic frustration in NiBr2 due to the competing interactions arising from its underlying triangular lattice. This magnetic frustration increases with pressure and is at the origin of the helimagnetic order. Further, pressure causes a sizable increase in the interlayer interactions. Our Monte Carlo simulations show that a large (threefold) increase in the helimagnetic transition temperature can be achieved at pressures of around 15 GPa. This indicates that hydrostatic pressure can indeed be used as a tuning knob to increase the magnetic transition temperature of NiBr2.