Ferroelectric transition induced by the incommensurate magnetic ordering in LiCuVO4

A ferroelectric transition occurring simultaneously with a helical spin order has been found in both the polycrystalline and single-crystal samples of LiCUVO4. The system has Cu2+ spins (s = 1/2) of the CuO2 chains formed of edge-sharing CuO4 squares. Possibly due to the frustrated nature caused by a competition between the nearest-neighbor and next-nearest-neighbor exchange interactions, Cu spins exhibit, as has been already reported, the helical magnetic order with the incommensurate modulation vector Q along the chain direction and with the helical axis e(3) perpendicular to the CuO4 squares. The electric polarization P can be understood by the recently predicted relation P proportional to Q x e(3). The transition temperature has been found to be gradually suppressed by the applied magnetic field.