Ferroelectricity and Giant Magnetocapacitance in Perovskite Rare-Earth Manganites
The relationships among magnetism, lattice modulation, and dielectric properties have been investigated for $R{\mathrm{MnO}}_{3}$ ($R=\mathrm{Eu},\text{ }\mathrm{Gd},\text{ }\mathrm{Tb},\text{ }\mathrm{and}\text{ }\mathrm{Dy}$). These compounds show a transition to an incommensurate lattice structure below their N\'eel temperature, and subsequently undergo an incommensurate-commensurate (IC-C) phase transition. For ${\mathrm{TbMnO}}_{3}$ and ${\mathrm{DyMnO}}_{3}$ it was found that the IC-C transition is accompanied by a ferroelectric transition, associated with a lattice modulation in the C phase. ${\mathrm{DyMnO}}_{3}$ shows a gigantic magnetocapacitance with a change of dielectric constant up to $\ensuremath{\Delta}\ensuremath{\epsilon}/\ensuremath{\epsilon}\ensuremath{\sim}500%$.