Coupled spin-1/2 antiferromagnetic chain Cs${}_2$LiRuCl${}_6$ with partially disordered crystal lattice

We determined the crystal structure of Cs${}_2$LiRuCl${}_6$, which was synthesized first in this work, and investigated its magnetic properties. Cs${}_2$LiRuCl${}_6$ has a hexagonal structure composed of linear chains of face-sharing RuCl${}_6$ and LiCl${}_6$ octahedra. In two-thirds of the structural chains, Ru${}^{3+}$ and Li${}^{+}$ sites are almost ordered, while in the other chains their sites are disordered. This situation is analogous to the ground state of the antiferromagnetic Ising model on a triangular lattice. Using electron paramagnetic resonance, we evaluated the $g$ factors of Ru${}^{3+}$ with effective spin-1/2 as $g_c=2.72$ and $g_{ab}=1.50$ for magnetic fields $H$ parallel and perpendicular to the $c$ axis, respectively. Magnetization curves for $H\parallel c$ and $H\perp c$ are highly anisotropic. However, these magnetization curves approximately coincide when normalized by the $g$ factors. It was found from the magnetization and specific heat results that Cs${}_2$LiRuCl${}_6$ can be described as a coupled one-dimensional $S=1\mathrm{/}2$ Heisenberg-like antiferromagnet with $J/k_{\rm B},{\simeq},3.7$K\mathrm{.}Three-dimensionalorderingoccursat$T_{\rm N},{=},0.48$K\mathrm{.}Amagneticphasediagramfor$H,{\parallel},c$ is also presented.