Magnetic-field dependence of the ferroelectric polarization and spin-lattice coupling in multiferroic MnWO$_4$
K. Taniguchi, N. Abe, H. Sagayama, S. Otani, T. Takenobu, Y. Iwasa, and T. Arima

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 takes incommensurate magnetic (ICM) structure also in a magnetic field. In the high-field (HF) phase, which appears in high magnetic fields above 12 T along the easy axis, the magnetic-field-induced ferroelectric polarization has disappeared.

© 2008 The American Physical Society.