Low-Energy Excitations probed by 51V NMR in the Multiferroic Ni3V2O8

We present results of the single-crystal V-51 NMR measurements in the multiferroic compound Ni3V2O8. V-51 Knight shifts in a magnetic field parallel to the b axis follow the Curie-Weiss law with the Weiss temperature, -9.5 K, comparable to the onset temperature of long-range magnetic order, T-HI = 9.4 K, where the high-temperature incommensurate magnetic order takes place. Non-linearity in the Knight shift vs magnetic susceptibility plot suggests the significant Dzyaloshinsky-Moriya interaction above T-HI. Despite three successive magnetic transitions below T-HI, the V-51 nuclear spin-lattice relaxation rate measured along the b axis shows a critical slowing down only at T-HI.