Spin-Singlet Ground State of Two-Dimensional Quantum Spin Antiferromagnet (CuCl)Ca2Nb3O10

We report structural and magnetic properties of the triple-layered perovskite (CuCl)Ca2Nb3O10 with a spin-1/2 CuCl layer, investigated by transmission electron microscopy, magnetic susceptibility, high-field magnetization, specific heat, µSR, and inelastic neutron scattering measurements. The results show that (CuCl)Ca2Nb3O10 has a spin-singlet ground state with a gap of Δ/kB = 11 K. The observation of a 2 × 2 superstructure suggests a coherent distortion of the CuCl square lattice as in the double-layered (CuCl)LaNb2O7 with Δ/kB = 14 K. The low-temperature magnetization exhibits a jump to saturation above the critical field of Hc = 7.8 T, in marked contrast to the case of (CuCl)LaNb2O7, where the magnetization slowly increases above Hc. The observed magnetic properties are discussed in terms of the ferromagnetic Shastry–Sutherland model.