New category of the frustrated quantum magnets composed of spin-1/2 triple-chains

Cu3(OH)4MO4, which is a natural mineral szenicsite, has been studied by the magnetic susceptibility, the specific heat, and the high field magnetization measurement. This compound consists of S = 1/2 triple-chain of the edge-sharing octahedra CuO6. On the basis of the crystal structure in szenicsite, spin frustration can strongly affect the ground state. The magnetic susceptibility has a broad maximum around 80 K, which is characteristic of the quasi-one-dimensional antiferromagnet. There are no sign of magnetic phase transitions from 300 K down to 2 K in our measurements. The magnetization curve measurement up to 48 T at 1.3 K indicates that neither magnetic order nor spin gap is present. Assuming the triple-chains as the isolated uniform chains, we estimated the dominant exchange interaction J/kB = -66 K.