Singlet ground state and spin gap in S=1/2 Kagome antiferromagnet Rb2Cu3SnF12

We investigated the crystal structure of Rb2Cu3SnF12 and its magnetic properties using single crystals. This compound is composed of Kagome layers of corner-sharing CuF6 octahedra with a 2a x 2a enlarged cell as compared with the proper Kagome layer. Rb2Cu3SnF12 is magnetically described as an S = 1/2 modified Kagome antiferromagnet with four kinds of neighboring exchange interaction. From magnetic susceptibility and high-field magnetization measurements, it was found that the ground state is a disordered singlet with the spin gap, as predicted from a recent theory. Exact diagonalization for a 12-site Kagome cluster was performed to analyze the magnetic susceptibility, and individual exchange interactions were evaluated.