Magnetic-field dependence of the ferroelectric polarization and spin-lattice coupling in multiferroic MnWO4

The magnetic-field dependence of the ferroelectric polarization and the spin-lattice coupling in multiferroic MnWO(4) have been investigated. The ferroelectric transition from the low temperature paraelectric phase occurs when the magnetic field is applied along the a, c, and the spin easy axes. The ferroelectric polarization in the magnetic field along the a and the c axis shows a contrasting behavior depending on the field direction, possibly reflecting the relative configuration between the crystallographic axis and the magnetic principal axis in the ac plane. Incommensurate lattice modulation observed in the ferroelectric spiral-spin phase confirms the existence of spin-lattice coupling in MnWO(4). The lattice modulation indicates that the ferroelectric AF2 phase also takes the incommensurate magnetic structure in a magnetic field. In the high-field phase, which appears in high magnetic fields above 12 T along the easy axis, the magnetic-field-induced ferroelectric polarization disappeared.