Singlet Ground State and Spin Gap in S=1⁄2 Kagomé Antiferromagnet Rb₂Cu₃SnF₁₂

抄録

We investigated the crystal structure of Rb₂Cu₃SnF₁₂ and its magnetic properties using single crystals. This compound is composed of Kagomé layers of corner-sharing CuF₆ octahedra with a 2a×2a enlarged cell as compared with the proper Kagomé layer. Rb₂Cu₃SnF₁₂ is magnetically described as an S=1⁄2 modified Kagomé 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 Kagomé cluster was performed to analyze the magnetic susceptibility, and individual exchange interactions were evaluated.