A ferroelectric transition occurring simultaneously with 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 the 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 e3 perpendicular to the CuO4 squares. The electric polarization P can be understood by the recently predicted relation (P is proportional to Q*e3). The transition temperature has been found to be gradually suppressed by the applied magnetic field.
@article{arxiv.cond-mat/0611659,
title = {Ferroelectric Transition Induced by the Incommensurate Magnetic Ordering in LiCuVO4},
author = {Yutaka Naito and Kenji Sato and Yukio Yasui and Yusuke Kobayashi and Yoshiaki Kobayashi and Masatoshi Sato},
journal= {arXiv preprint arXiv:cond-mat/0611659},
year = {2015}
}