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 ${\mathrm{VBr}}₃$ through various experimental techniques. With decreasing the temperature, ${\mathrm{VBr}}₃$ 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 ${\mathrm{VBr}}₃$ 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 ${\mathrm{VI}}₃$ always have clear hysteresis loops in all magnetic field directions. Magnetization measurements of angle for rotation in both $ab$ and $ac$ planes also suggest ${\mathrm{VBr}}₃$ 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 ${E}_{\mathrm{g}}$ 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 ${\mathrm{VBr}}₃$ changes from $R\overline{3}$ structure to $C2/m$ structure with stacking order change as temperature decreases.