Ferroelectric Polarization Flop in a Frustrated MagnetMnWO4Induced by a Magnetic Field

The relationship between magnetic order and ferroelectric properties has been investigated for ${\mathrm{MnWO}}_4$ with a long-wavelength magnetic structure. Spontaneous electric polarization is observed in an elliptical spiral spin phase. The magnetic-field dependence of electric polarization indicates that the noncollinear spin configuration plays a key role for the appearance of the ferroelectric phase. An electric polarization flop from the $b$ direction to the $a$ direction has been observed when a magnetic field above 10 T is applied along the $b$ axis. This result demonstrates that an electric polarization flop can be induced by a magnetic field in a simple system without rare-earth $4f$ moments.