  Electric control of multiferroic domains is demonstrated through polarized
magnetic neutron diffraction. Cooling to the cycloidal multiferroic phase of
Ni3V2O8 in an electric field (E) causes the incommensurate Bragg reflections to
become neutron spin polarizing, the sense of neutron polarization reversing
with E. Quantitative analysis indicates the E-treated sample has handedness
that can be reversed by E. We further show close association between cycloidal
and ferroelectric domains through E-driven spin and electric polarization
hysteresis. We suggest that definite cycloidal handedness is achieved through
magneto-elastically induced Dzyaloshinskii-Moriya interactions.
