Spin-modulated quasi-1D antiferromagnet LiCuVO4

We report on magnetic resonance studies within the magnetically ordered phase of the quasi-1D antiferromagnet LiCuVO_4. Our studies reveal a spin reorientational transition at a magnetic field H_c1 ~ 25 kOe applied within the crystallographical (ab)-plane in addition to the recently observed one at H_c2 \~75 kOe [ M.G. Banks et al., cond-mat/0608554 (2006)]. Spectra of the antiferromagnetic resonance (AFMR) along low-frequency branches can be described in the frame of a macroscopic theory of exchange-rigid planar magnetic structures. These data allow to obtain the anisotropy of the exchange interaction together with a constant of the uniaxial anisotropy. Spectra of 7Li nuclear magnetic resonance (NMR) show that, within the magnetically ordered phase of LiCuVO_4 in the low-field range H H_c2 ~ 75 kOe, our NMR spectra simulations show that the magnetically ordered structure exhibits a modulation of the spin projections along the direction of the applied magnetic field H.