Correlation between ferroelectric polarization and sense of helical spin order in multiferroic MnWO4

We report a polarized-neutron-diffraction study on a single crystal sample of MnWO4, wherein the ferroelectricity and spiral magnetic order coexist. The direction of electric polarization controls the sense of helix that can be detected from the difference in intensities of magnetic satellites for parallel and antiparallel spin directions of incident neutrons with respect to a scattering vector. The temperature dependence of the difference agrees well with that of the electric polarization. These results corroborate that an inverse effect of a Dzyaloshinskii-Moriya interaction is the origin of the spontaneous electric polarization in the spiral phase of MnWO4.