Structural and magnetic phase transitions in quasi-two-dimensional VBr3

We present a systematic study on the structural and magnetic phase transitions in quasi-two-dimensional (2D) material VBr3 through various experimental techniques. With decreasing the temperature, VBr3 first undergoes a structural phase transition at around 90 K and then changes into the antiferromagnetic (AFM) state below 26.5 K. Interestingly, in addition to the strong AFM coupling background below 26.5 K, our VBr3 single crystals also exhibit robust hysteresis loops with coercive field about 1.5 T at 2 K for H//c, but none for H//ab. This is a typical feature of canted AFM and should not originate from a possible ferromagnetic (FM) impurities phase, because FM materials such as VI3 always have clear hysteresis loops in all magnetic field directions. Magnetization measurements of angle for rotation in both ab and ac planes also suggest VBr3 as a canted AFM with easy axis slightly off the c axis. Furthermore, detailed Raman spectroscopy measurements also reveal the structural phase transition at 90 K. More importantly, splitting of a doubly degenerated E-g mode is observed, which demonstrates threefold rotational symmetry breaking in the low-temperature phase. Considering the similar structural phase transition of isostructural materials, we conclude that VBr3 changes from R (3) over bar structure to C2/m structure with stacking order change as temperature decreases.