High-pressure magnetization and NMR studies of α−RuCl3

Abstract

We report high-pressure magnetization and 35 Cl NMR studies on α-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 Tx increased to 250 K at 1 GPa. The 1/ 35 T1 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.

Pressure-induced dimerization and valence bond crystal formation in the Kitaev-Heisenberg magnet α−RuCl3

“…The transition temperature T S2 increases rapidly with pressure and reaches room temperature around p = 1.3 GPa. This phase diagram is in good agreement with previous studies under hydrostatic pressure [24,25] and further shows that the pressure-induced transition is of a first-order nature. In order to elucidate the microscopic mechanisms underlying the pressure-induced transition at T S2 , we performed high-resolution XRD under hydrostatic pressure.…”

“…The pressure-induced collapse of the in-plane magnetization in Ref. [25] with an AB stacking seems shifted to higher pressure compared to the one reported here and shows a phase separation regime on a broader pressure range up to at least p 1 GPa. This difference suggests that the stacking sequence would have a small influence on the structural transition T S2 .…”

“…However, the initial slope value dT N /dp p=0 −23 K/GPa from thermal expansion is in contradiction with the phase diagram drawn by the other techniques under the application of hydrostatic pressure [24,25]. Magnetization measurements indicate a reduction of the inplane magnetization and a high-temperature transition of unknown origin, while NMR indicates no long-range magnetic order and gapped magnetic fluctuations in the high-pressure state [25]. Furthermore, electrical resistivity studies under hydrostatic pressure exclude the possibility of a pressureinduced insulator-to-metal transition [24].…”

“…While the authors in Ref. [25] measured the magnetic susceptibility on a single crystal with a single Néel temperature T N 13.6 K, indicating an AB stacking of the honeycomb layers [9], the measurements reported here were performed on a single crystal with an ABC stacking, as indicated by T N 7 K [9]. The pressure-induced collapse of the in-plane magnetization in Ref.…”

“…While electronic-structure calculations indicate that K is ferromagnetic in α-RuCl 3 and indeed defines the largest exchange energy scale [7,8,14,15], the debate on the minimal effective spin model and precise magnitude of the different couplings is not fully settled yet. By applying a magnetic field in the basal plane, the magnetic zigzag ground state can be suppressed [6,16,17] and the phase above this transition was identified as a quantum spin liquid, by NMR [18], thermal conductivity [19][20][21], terahertz spectroscopy [22], and neutron scattering experiments [23].Further, it was very recently shown by specific heat, magnetization, and NMR measurements [24,25] that the Néel …”