Multiferroicity in the frustrated spinel cuprate GeCu$_2$O$_4$

TL;DR

This study reports the discovery of spin-induced multiferroicity in GeCu$_2$O$_4$, a frustrated spinel cuprate, revealing weak ferroelectric polarization associated with magnetic ordering at 33 K, which constrains theoretical models of its magnetic ground state.

Contribution

First observation of ferroelectric polarization in GeCu$_2$O$_4$, demonstrating multiferroicity linked to its magnetic structure, with implications for understanding frustrated spinel systems.

Findings

Ferroelectric polarization emerges at T_N ~ 33 K.

Weak polarization magnitude (~0.2 μC/m²).

Spin-induced multiferroicity constrains magnetic models.

Abstract

Different from other magnetically frustrated spinel systems, GeCu$_{2}$O$_{4}$ is a strongly tetragonal distorted spinel cuprate in which edge-sharing CuO$_{2}$ ribbons are running along alternating directions perpendicular to the $c$-axis. Here, GeCu$_{2}$O$_{4}$ samples of high quality were prepared via high pressure synthesis (at 4 GPa) and the corresponding magnetic and dielectric properties were investigated. For the first time, we observed a ferroelectric polarization emerging at T$_{N}$ $\sim$ 33~K. Although the ferroelectric polarization is weak in GeCu$_{2}$O$_{4}$ ($P$ $\sim$ 0.2$\mu$C/m$^{2}$), the existence of spin-induced multiferroicity provides a strong constraint on the possible ground state magnetic structures and/or the corresponding theoretical models of multiferroicity for GeCu$_{2}$O$_{4}$.