Absence of magnetic order and quantum magnetization plateau in spin-1/2 tetramer compound K2Co2Mo3O12

A Seff = 1/2 tetramer antiferromagnet K2Co2Mo3O12 has been synthesized and its structure and magnetism are investigated. The magnetic susceptibility and electronic spin resonance show that the compound has no long-range order down to 0.5 K, although there is a large negative Curie-Weiss temperature. The high-field magnetization curve at 2 K measured up to 30 T exhibits two magnetic transitions at Hc1 = 4.4 T and Hc2 = 8.7 T, which are associated with 1/2 quantum magnetization plateau. The magnetization process can be well fitted by isolated Co4 tetramer model with anisotropic exchange interactions and g-factors. Thus, the title compound should be described as a weakly interacting spin-1/2 tetramer antiferromagnet with strong anisotropy of exchanges.