Spin-modulated quasi-1D antiferromagnet LiCuVO_4

TL;DR

This study investigates the magnetic resonance properties of LiCuVO_4, revealing spin reorientations and detailed magnetic structures through experimental and theoretical analysis, including NMR and AFMR techniques.

Contribution

It provides new insights into the spin reorientational transitions and magnetic structures of LiCuVO_4 using combined NMR and AFMR studies, supported by theoretical modeling.

Findings

Identification of spin reorientational transitions at H_c1 and H_c2.

Confirmation of a planar spiral spin structure in the low-field phase.

Observation of spin modulation along the magnetic field at high fields.

Abstract

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_c1, a planar spiral spin structure is realized with the spins lying in the (ab)-plane in agreement with neutron scattering studies of B.J. Gibson et al. [Physica B Vol. 350, 253 (2004)]. Based on NMR spectra simulations, the transition at H_c1 can well be described as a spin-flop transition, where the spin plane of the magnetically ordered structure rotates to be perpendicular to the direction of the applied magnetic field. For 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.