NMR investigation of BaCu₂V₂O₈ in alternating-chain and dimer-chain models

⁵¹V NMR measurements were performed on the quasi-one-dimensional compound BaCu₂V₂O₈. Two ⁵¹V NMR lines that are associated with two vanadium crystallographic sites have been resolved. For each site the temperature-dependent NMR shift exhibits a character of low-dimensional magnetism with a broad maximum at T_max≃280 K. Below T_max, the NMR shifts and spin-lattice relaxation rates clearly indicate activated behavior, confirming the spin gap formation in BaCu₂V₂O₈. While the alternating-chain model has been proposed to account for the observed spin gap characteristics, our NMR results suggest that the nearly isolated dimer picture could be an alternative scenario for the understanding of the gap feature in this material.