Enhancement of giant magnetoelectric effect in Ni-doped CaBaCo$_{4}$O$_{7}$

TL;DR

This study demonstrates that Ni doping in CaBaCo$_{4}$O$_{7}$ significantly enhances its giant magnetoelectric effect, increasing electric polarization change and expanding the temperature range of this phenomenon.

Contribution

It reveals that small Ni substitution in CaBaCo$_{4}$O$_{7}$ amplifies the magnetoelectric effect and broadens the temperature range of giant polarization change.

Findings

Giant positive polarization change up to 12 mC/m$^{2}$ observed under magnetic field.

Ni doping introduces two antiferromagnetic phases below 78 K.

Enhanced magnetoelectric effect with increased magnitude and temperature range.

Abstract

The polar magnet CaBaCo$_{4}$O$_{7}$ is known to exhibit the largest magnetic-field-driven electric polarization change ($\Delta P$) associated with an antiferromagnetic (AFM)-ferrimagnetic (FIM) transition in a narrow temperature range between 62 and 69 K. In this work, we investigate the effect of Ni doping on its multiferroic properties, by means of magnetization, electric polarization, dielectric constant, and magnetostriction measurements on single crystals of CaBaCo$_{3.9}$Ni$_{0.1}$O$_{7}$ up to 50 T. In the doped material, two kinds of AFM phases appear below 78 K, accompanying negative $\Delta P$. Upon the application of a magnetic field along any crystallographic axis, giant positive $\Delta P$ of up to $11 \sim 12$ mC/m$^{2}$ is observed along with an AFM-FIM transition in the whole temperature range below 78 K. The giant magnetoelectric effect inherent in CaBaCo$_{4}$O$_{7}$ can be further enhanced just by a small amount of chemical substitution, in terms of (i) increasing the magnitude of $\Delta P$ and (ii) expanding the temperature range in which giant $\Delta P$ appears.