We report α-Cu2V2O7 to be an improper multiferroic with the simultaneous development of electric polarization and magnetization below TC = 35 K. The observed spontaneous polarization of magnitude 0.55 μCcm−2 is highest among the copper based improper multiferroic materials. Our study demonstrates sizable amount of magneto-electric coupling below TC even with a low magnetic field. The theoretical calculations based on density functional theory (DFT) indicate magnetism in α-Cu2V2O7 is a consequence of {\em ferro-orbital} ordering driven by polar lattice distortion due to the unique pyramidal (CuO5) environment of Cu. The spin orbit coupling (SOC) further stabilize 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.
@article{arxiv.1501.00809,
title = {Exchange striction induced giant ferroelectric polarization in copper based multiferroic material $\alpha$-Cu$_2$V$_2$O$_7$},
author = {J. Sannigrahi and S. Bhowal and S. Giri and S. Majumdar and I. Dasgupta},
journal= {arXiv preprint arXiv:1501.00809},
year = {2015}
}