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 str ucture. The magnetic susceptibility and the high-field magnetization proces s were investigated in order to elucidate the ground state of this spin cha in system. From the results, the ground state of this compound appears to b e an antiferromagnetic ally ordered state. The transition temperature was d etermined to be T-N = 7.8 K. However, there are some anomalous behaviors ev ident in both the susceptibility and the magnetization curves: the Curie co nstant 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. Assumi ng 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 clas sical renormalized ordered state may coexist with the quantum disordered st ate. Two conceivable models have been proposed for the ground state.