Hydrated lithium intercalation into the Kitaev spin liquid candidate material $\alpha \text{−}{\mathrm{RuCl}}_3$

We study the transport and magnetic properties of hydrated and lithium-intercalated $\alpha \text{−}{\mathrm{RuCl}}_3,{\mathrm{Li}}_x{\mathrm{RuCl}}_3·y{\mathrm{H}}_2\mathrm{O}$, to investigate the effect on mobile-carrier doping into candidate materials for a realization of a Kitaev model. From thermogravimetric and one-dimensional electron map analyses, we find two crystal structures of this system, that is, monolayer hydrated ${\mathrm{Li}}_x{\mathrm{RuCl}}_3·y{\mathrm{H}}_2\mathrm{O}(x\approx 0.56,y\approx 1.3)$ and bilayer hydrated ${\mathrm{Li}}_x{\mathrm{RuCl}}_3·y{\mathrm{H}}_2\mathrm{O}(x\approx 0.56,y\approx 3.9)$. The temperature dependence of the electrical resistivity shows a temperature hysteresis at 200–270 K, which is considered to relate to the formation of a charge order. The antiferromagnetic order at 7–13 K in pristine $\alpha \text{−}{\mathrm{RuCl}}_3$ is successfully suppressed down to 2 K in bilayer hydrated ${\mathrm{Li}}_x{\mathrm{RuCl}}_3·y{\mathrm{H}}_2\mathrm{O}$, which is sensitive to not only the electronic state of Ru but also the interlayer distance between Ru-Cl planes.

Figure 1

X-ray diffraction patterns for (a) polycrystals of samples A–E and (b) single crystals of samples F–H. The vertical axis is in a logarithmic scale. The Miller indexes on the basis of the monoclinic $C2/m$ are also shown.

Figure 2

Thermogravimetric analysis for samples A, B, and D in the heating process up to $600{}^{\circ }\mathrm{C}$ at $1^{\circ }\mathrm{C}/\min$. The temperature dependence of weight loss is shown.

Figure 3

One-dimensional electron density map ${\rho }_z$ and the structural model of the $ac$ plane for single crystals of (a) ${\mathrm{RuCl}}_3$ (sample F) and (b) MLH- and (c) BLH-${\mathrm{Li}}_x{\mathrm{RuCl}}_3·y{\mathrm{H}}_2\mathrm{O}$ (samples G and H).

Figure 4

Arrhenius plot of the in-plane resistivity $\rho$ for single crystals of ${\mathrm{RuCl}}_3$ and MLH- and BLH-${\mathrm{Li}}_x{\mathrm{RuCl}}_3·y{\mathrm{H}}_2\mathrm{O}$ (samples F–H). The inset shows the resistivity in cooling and warming cycles, which are represented by solid and open symbols, respectively, in the vicinity of the phase transition temperature $T^{*}$.

Figure 5

Temperature dependences of magnetic susceptibility $\chi$ of single crystals of (a) ${\mathrm{RuCl}}_3$ and (b) MLH- and (c) BLH-${\mathrm{Li}}_x{\mathrm{RuCl}}_3·y{\mathrm{H}}_2\mathrm{O}$ at a magnetic field of ${\mu }_{0}H=1$ T parallel to the $ab$ plane (open symbols) and the $c$ axis (solid symbols). Insets are enlarged plots at low temperatures. (d) Curie-Weiss plot of $\chi$ under the magnetic fields parallel to the $ab$ plane. The inset of (d) is the dependence of an antiferromagnetic transition temperature $T_{\mathrm{N}}\text{on}$ the interlayer distance $c^{*}$.