Magnetoelectric effect and magnetic phase diagram of a polar ferrimagnetCaBaFe4O7

Abstract

The magnetic phase diagram of a polar ferrimagnet ${\mathrm{CaBaFe}}_{4}{\mathrm{O}}_{7}$ with a magnetic easy axis has been investigated by measurements of magnetization, specific heat, and magnetoelectricity. A ferrimagnetic transition takes place at ${T}_{\mathrm{C}1}=275$ K within the orthorhombic phase followed by a second magnetic transition at ${T}_{\mathrm{C}2}=211$ K. Below ${T}_{\mathrm{C}2}$, successive metamagnetic transitions occur for magnetic fields applied perpendicular to the easy axis, implying a sequential emergence of magnetic states which are neither collinear nor coplanar. The observation of the static magnetoelectric effect was limited to temperatures below 120 K due to the conducting nature of the crystals at higher temperatures. The magnitude of the ferroelectric polarization shows large changes between the different field-induced magnetic phases. The low-field state is characterized by a large linear magnetoelectric coefficient of ${\ensuremath{\alpha}}_{cc}=39$ ps/m, while a gigantic polarization change of $\mathrm{\ensuremath{\Delta}}P=850 \ensuremath{\mu}\mathrm{C}/{\mathrm{m}}^{2}$ is observed for ${\ensuremath{\mu}}_{o}H=14$ T applied along the easy axis.