Novel Frustrated Spin Chain System in KCu₅V₃O₁₃

A powder sample of KCu₅V₃O₁₃ was synthesized and is expected to represent a novel frustrated spin chain system based on its characteristic crystal structure. The magnetic susceptibility and the high-field magnetization process were investigated in order to elucidate the ground state of this spin chain system. From the results, the ground state of this compound appears to be an antiferromagnetically ordered state. The transition temperature was determined to be T_N = 7.8 K. However, there are some anomalous behaviors evident in both the susceptibility and the magnetization curves: the Curie constant and the Weiss temperature change markedly around 75 K, the gradient of the magnetization curve becomes small after a spin-flop transition, and the number of the ordered spins is only 1/5 of all the copper spins. Assuming that the other spins vanish by forming a spin-singlet state, the energy gap was estimated to be 44.3 K from the magnetization curve. Thus, the classical renormalized ordered state may coexist with the quantum disordered state. Two conceivable models have been proposed for the ground state.