Observation of Spin Gap in CaV_2O_5 by NMR

Abstract

The Knight shift (K) and the spin-lattice relaxation rate (1/T₁) at the V site of CaV₂O₅ have been measured by means of the pulsed-NMR technique in order to investigate the magnetic properties. By analyzing the temperature dependence of the spin susceptibility extracted from the Knight shift, it was clarified for the first time that the ground state of the spin system in CaV₂O₅ is a spin singlet state. Moreover, the energy gap between the ground state and the excited state was estimated to be about 500, K from the activation-like behavior of χ and 1/T₁. These results clearly indicate the existence of the spin gap in this material.