Crystal growth and characterization of the frustrated spin systems Cs${}_{2-x}$Rb${}_x$CuCl${}_4$

Crystals of the antiferromagnetic insulator Cs${}_2$CuCl${}_4$ and the substitution series (Cs${}_{2-x}$Rb${}_x$)CuCl${}_4$ (x = 0.1, 0.2) were grown by vertical Bridgman method. The controlled substitution of cesium atoms with the smaller rubidium, causes chemical pressure on the crystal lattice. The essential magnetic units in these systems are Jahn-Teller distorted (CuCl${}_4$) tetrahedra, which are arranged in layers separated by the alkali atoms. These layers form a triangular lattice of localized Cu${}^{2+}$ spins, where the spins interact through exchange couplings. The resulting geometric frustration leads to quantum spin-liquid properties at low temperatures. In addition to the growth and characterization of (Cs${}_{2-x}$Rb${}_x$)CuCl${}_4$, we discuss the structural changes in the lattice parameters and the magnetic behavior of the substituted system in comparison to the well understood parent compound Cs${}_2$CuCl${}_4$.