Magnetic field driven 2D-3D crossover in theS=12frustrated chain magnetLiCuVO4

Abstract

We report on a heat-capacity study of high-quality single-crystal samples of ${\mathrm{LiCuVO}}_{4}$---a frustrated spin $S=\frac{1}{2}$ chain system---in a magnetic field amounting to 3/4 of the saturation field. A detailed examination of magnetic phase transitions observed in this field range shows that although the low-field helical state clearly has three-dimensional properties, the field-induced spin-modulated phase turns out to be quasi-two-dimensional. The model proposed in this paper allows one to qualitatively understand this crossover, thus eliminating the presently existing contradictions in the interpretations of NMR and neutron-scattering measurements.