Switching the ferroelectric polarization in the S=1/2 chain cuprate LiCuVO4 by external magnetic fields

We present a detailed study of the complex dielectric constant and the ferroelectric polarization in multiferroic LiCuVO4 as function of temperature and external magnetic field. In zero external magnetic field, a spiral spin order with an ab helix and a propagation vector along the crystallographic b direction is established, which induces ferroelectric order with spontaneous polarization parallel to a. The direction of the helix can be reoriented by an external magnetic field and allows switching of the spontaneous polarization. We find a strong dependence of the absolute value of the polarization for different orientations of the spiral plane. Above 7.5 T, LiCuVO4 reveals collinear spin order and remains paraelectric for all field directions. Thus, this system is ideally suited to check the symmetry relations for spiral magnets as predicted theoretically. The strong coupling of ferroelectric and magnetic order is documented and the complex (H,T) phase diagram is fully explored.