Relationship between magnetic structure and ferroelectricity of LiVCuO4

Neutron scattering studies and measurements of the dielectric susceptibility epsilon and ferroelectric polarization P have been carried out under various magnetic fields H for single-crystal samples of the multiferroic system LiVCuO4 with quasi one-dimensional spin 1/2 Cu2+ chains formed of edge-sharing CuO4 square planes, and the relationship between the magnetic structure and ferroelectricity has been studied. The ferroelectric polarization is significantly suppressed by the magnetic field H above 2T applied along the a and b axes. When H = 0, a helical magnetic structure with the helical axis parallel to c has been confirmed. The magnetic structure under the field along a has been deter-mined, where the ab-plane structure changes to the helical one with the helical axis parallel to H with increasing the field through similar to 2 T. The ferroelectric polarization along a at H = 0 is found to be proportional to the neutron magnetic scattering intensity, indicating that the magnetic order is closely related to the appearance of the ferroelectricity. The relationship between the magnetic structure and ferroelectricity of LiVCuO4 is discussed by considering the existing theories.