High-pressure magnetization and NMR studies of α−RuCl3

We report high-pressure magnetization and $^{35}\mathrm{Cl}$ NMR studies on $\ensuremath{\alpha}\text{\ensuremath{-}}{\mathrm{RuCl}}_{3}$ 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 ${T}_{N}$ shows a concave shape dependence with pressure. These data suggest stacking rearrangement along the $c$ axis. With increasing pressure, phase separation appears prominently at $P\ensuremath{\ge}$ 0.45 GPa, and the magnetic volume fraction is completely suppressed at $P\ensuremath{\ge}$ 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 $1{/}^{35}{T}_{1}$ 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.