Electric Control of Spin Helicity in Multiferroic Triangular Lattice Antiferromagnet CuCrO2 with Proper-Screw Order

We have carried out a spin-polarized-neutron study on multiferroic CuCrO2 to clarify the origin of the ferroelectricity. The neutron results demonstrate that an incommensurate proper-screw magnetic structure of CuCrO2 induces electric polarization. Not only the magnetic structure but also the oxygen location contributes to the ferroelectricity of CuCrO2. The electric polarization of CuCrO2 can be explained not by a conventional spin-current model but by a theoretical prediction proposed by Arima. The spin helicities of CuCrO2 can be reversed by the reversal of the electric field E in the multiferroic phase.