Multiferroicity in the frustrated spinel cuprate GeCu2O4

Different from other magnetically frustrated spinel systems, ${\mathrm{GeCu}}₂{\mathrm{O}}₄$ is a strongly tetragonal distorted spinel cuprate in which edge-sharing ${\mathrm{CuO}}₂$ ribbons are running along alternating directions perpendicular to the $c$ axis. Here, ${\mathrm{GeCu}}₂{\mathrm{O}}₄$ samples of high quality were prepared via high-pressure synthesis (at 4 GPa) and the corresponding magnetic and dielectric properties were investigated. We observed a ferroelectric polarization emerging at ${T}_N\ensuremath{\sim}33$ K. Although the ferroelectric polarization is weak in ${\mathrm{GeCu}}₂{\mathrm{O}}₄\phantom{\rule{4pt}{0ex}}(P\ensuremath{\sim}0.2\phantom{\rule{0.28em}{0ex}}\ensuremath{\mu}\mathrm{C}/{\mathrm{m}}²)$, 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 ${\mathrm{GeCu}}₂{\mathrm{O}}₄$.