High-pressure magnetization and NMR studies of α-RuCl3

We report high-pressure magnetization and Cl-35 NMR studies on alpha-RuCl3 with pressure up to 1.5 GPa. At low pressures, the magnetic ordering is identified by both the magnetization data and the NMR data, where the TN shows a concave shape dependence with pressure. These data suggest stacking rearrangement along the c axis. With increasing pressure, phase separation appears prominently at P >= 0.45 GPa, and the magnetic volume fraction is completely suppressed at P >= 1.05 GPa. Meanwhile, a phase-transition-like behavior emerges at high pressures in the remaining volume by a sharp drop of magnetization M(T) upon cooling, with the transition temperature T-x increased to 250 K at 1 GPa. The 1/T-35(1) is reduced by over three orders of magnitude when cooled below 100 K. This characterizes a high-pressure, low-temperature phase with nearly absent static susceptibility and low-energy spin fluctuations. The nature of the high-pressure ground state is discussed, where a magnetically disordered state is proposed as a candidate state.