NMR study of the high-field magnetic phase of LiCuVO4

We report on NMR studies of the quasi-one-dimensional antiferromagnetic S= 1/2 chain cuprate LiCuVO4, focusing on the high-field spin-modulated phase observed recently in applied magnetic fields H > H-c2(mu H-0(c2) approximate to 7.5 T). The NMR spectra of Li-7 and V-51 around the transition from the ordered to the paramagnetic state were measured. It is shown that the spin-modulated magnetic structure forms with ferromagnetic interactions between spins of neighboring chains within the ab plane at low temperatures 0.6 K < T < T-N. The best fit provides evidence that the mutual orientation between spins of neighboring ab planes is random. For higher temperatures T-N < T less than or similar to 15 K, short-range magnetic order occurs at least on the characteristic time scale of the NMR experiment.