Magnetic properties of the novel frustrated lattice magnet likasite

Magnetic properties of Cu-3(OH)(5)(NO3)center dot 2H(2)O (likasite) are studied by measuring magnetic susceptibility, specific heat and high field magnetization up to 73 T. Weiss temperature is estimated to be -16 K, and the dominant magnetic interaction in likasite is found to be antiferromagnetic. The magnetic susceptibility has a round maximum at around 12 K, which is a characteristic of low-dimensional antiferromagnets. A long range magnetic order is not observed down to 2 K, suggesting the spin frustration effect. The high field magnetization measured at 1.3 K and 4.2 K appears to saturate above 40 T but the "saturation" value is only 2/3 of the expected saturation magnetization. This result is compared with the 2/3 magnetization plateau, theoretically suggested to stabilize in the diamond chain spin model by additional inter-monomer interactions.