On the nature of the spin frustration in the CuO2 ribbon chains of LiCuVO4: Crystal structure determination at 1.6 K, magnetic susceptibility analysis and density functional evaluation of the spin exchange constants

The spin-1/2 Cu2+ ions of LiCuVO4 form one-dimensional chains along the b-direction, and the spin frustration in LiCuVO4 is described in terms of the nearest-neighbor ferromagnetic exchange J1 and the next-nearest-neighbor antiferromagnetic exchange J2 in these chains. Recently, it has become controversial whether or not J1 is stronger in magnitude than J2. To resolve this controversy, we determined the crystal structure of LiCuVO4 at 1.6 K by neutron diffraction, analyzed the magnetic susceptibility of LiCuVO4 to deduce the Curie-Weiss temperature \theta and the J2/J1 ratio, and finally extracted the spin exchange constants of LiCuVO4 on the basis of density functional calculations. Our work shows unambiguously that the Curie-Weiss temperature \theta of LiCuVO4 is negative in the range of -20 K, so that J2 is substantially stronger in magnitude than J1.