Magnetic field control of the ferroelectric polarization in multiferroic MnWO$_{4}$

The relationship between magnetic order and ferroelectric properties has been investigated for MnWO$_{4}$. Spontaneous electric polarization is observed in a cycloidal spiral spin phase. The magnetic-field dependence of electric polarization indicates that the noncollinear spin configuration plays a key role for the appearance of ferroelectric phase. Destabilization of the ferroelectric phase and an electric polarization flop from the $b$ direction to the $a$ direction have been observed when a magnetic field is applied along the $b$ axis. On the other hand, the ferroelectric phase is stabilized when a magnetic field is applied along the $a$-, $c$- and the spin easy axes. We have also found that the magnetic field induced ferroelectric polarization disappears in a high magnetic field above 12T along the spin easy axis. Theses phenomena provide us useful information for gigantic magnetoelectric effects because MnWO$_{4}$ is a simple system without rare-earth f-moments.