Exchange striction induced giant ferroelectric polarization in copper based multiferroic material $\alpha$-Cu$_2$V$_2$O$_7$

TL;DR

This study reveals that $ ext{α}$-Cu$_2$V$_2$O$_7$ is an improper multiferroic with giant polarization driven by exchange striction, showing strong magneto-electric coupling and unique orbital ordering mechanisms.

Contribution

The paper demonstrates the giant ferroelectric polarization in $ ext{α}$-Cu$_2$V$_2$O$_7$ driven by exchange striction, supported by both experimental and theoretical analysis.

Findings

Spontaneous polarization of 0.55 μC/cm² observed.

Strong magneto-electric coupling below 35 K.

Giant polarization primarily due to symmetric exchange-striction.

Abstract

We report $\alpha$-Cu$_2$V$_2$O$_7$ to be an improper multiferroic with the simultaneous development of electric polarization and magnetization below $T_C$ = 35 K. The observed spontaneous polarization of magnitude 0.55 $\mu$Ccm$^{-2}$ is highest among the copper based improper multiferroic materials. Our study demonstrates sizable amount of magneto-electric coupling below $T_C$ even with a low magnetic field. The theoretical calculations based on density functional theory (DFT) indicate magnetism in $\alpha$-Cu$_2$V$_2$O$_7$ is a consequence of {\em ferro-orbital} ordering driven by polar lattice distortion due to the unique pyramidal (CuO$_{5}$) 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.