Enhanced Ferroelectric Polarization by Induced Dy Spin Order in MultiferroicDyMnO3

Abstract

Neutron powder diffraction and single crystal x-ray resonant magnetic scattering measurements suggest that Dy plays an active role in enhancing the ferroelectric polarization in multiferroic ${\mathrm{DyMnO}}_3$ above $T_N^{\mathrm{Dy}}=6.5\mathrm{K}$. We observe the evolution of an incommensurate ordering of Dy moments with the same periodicity as the Mn spiral ordering. It closely tracks the evolution of the ferroelectric polarization. Below $T_N^{\mathrm{Dy}}$, where Dy spins order commensurately, the polarization decreases to values similar for those of ${\mathrm{TbMnO}}_3$. The higher $P_s$ found just above $T_N^{\mathrm{Dy}}$ arises from the contribution of Dy spins so as to effectively increase the amplitude of the Mn spin spiral.