NMR studies of incommensurate quantum antiferromagnetic state of LiCuVO$_{4}$

We report $^{51}$V NMR measurements in the linear spin-chain compound LiCuVO$_{4}$ single crystals. High temperature $^{51}$V spectra exhibit a classic quadrupole-split line expected for $I$ = 7/2 nuclei (splitting disappears below 50K). Linewidth anomalies correlated with characteristic features of the resonance shift were observed near 25K, 6K, and 2K. This is attributed to increased spin correlations leading to 3D antiferromagnetic order at low temperatures. The Knight shift tracks susceptibility giving a transfered hyperfine field of A$_{hf }$ = 6.5 kOe/$\mu _{B}$ on the V nuclei. Below 2K for a field parallel to crystal $c$-axis the spectra exhibit a broad two-peak feature which is absent for field along the $b$-axis. The moment orientation determined from the spectra suggests an incommensurate AF modulation along the $b$-axis in agreement with recent neutron scattering data.$^{1}$ Spin dynamics through relaxation measurements will be discussed. $^{1}$ B. J. Gibson, \textit{et al.,} Physica B350, e253 (2004).