Observation of spin gap in CaV2O5 by NMR

The Knight shift (K) and the spin-lattice relaxation rate (1/T-1) 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 chi and 1/T-1. These results clearly indicate the existence of the spin gap in this material.