Exchange-striction induced giant ferroelectric polarization in copper-based multiferroic materialα−Cu2V2O7

Abstract

We report $\ensuremath{\alpha}\ensuremath{-}{\mathrm{Cu}}_{2}{\mathrm{V}}_{2}{\mathrm{O}}_{7}$ to be an improper multiferroic with the simultaneous development of electric polarization and magnetization below ${T}_{C}=35\phantom{\rule{0.28em}{0ex}}\mathrm{K}$. The observed spontaneous polarization of $0.55\phantom{\rule{0.28em}{0ex}}\ensuremath{\mu}\mathrm{C}\phantom{\rule{0.16em}{0ex}}{\mathrm{cm}}^{\ensuremath{-}2}$ magnitude is highest among copper-based improper multiferroic materials. Our study demonstrates a sizable amount of magnetoelectric coupling below ${T}_{C}$, even with a low magnetic field. The theoretical calculations based on density functional theory indicate magnetism in $\ensuremath{\alpha}\ensuremath{-}{\mathrm{Cu}}_{2}{\mathrm{V}}_{2}{\mathrm{O}}_{7}$ is a consequence of ferro-orbital ordering driven by a polar lattice distortion due to the unique pyramidal (${\mathrm{CuO}}_{5}$) environment of Cu. Spin-orbit coupling further stabilizes orbital ordering and is crucial for magnetism. The calculations indicate that the origin of the giant ferroelectric polarization is primarily due to the symmetric exchange-striction mechanism and is corroborated by temperature-dependent x-ray studies.