Magnetic enhancement of ferroelectric polarization in a self-grown ferroelectric-ferromagnetic composite

Abstract

Ferroelectric-ferromagnetic multiferroic composites are of great interest both from the scientific and technological standpoints. The extent of coupling between polarization and magnetization in such two-phase systems depends on how efficiently the magnetostrictive and electrostrictive/piezoelectric strain gets transferred from one phase to the other. This challenge is most profound in the easy to make 0-3 ferroelectric-ferromagnetic particulate composites. Here we report a self-grown ferroelectric-ferromagnetic 0-3 particulate composite through controlled spontaneous precipitation of ferrimagnetic barium hexaferrite phase ($\mathrm{BaF}{\mathrm{e}}_{12}{\mathrm{O}}_{19}$) amid ferroelectric grains in the multiferroic alloy system $\mathrm{BiFe}{\mathrm{O}}_{3}\ensuremath{-}\mathrm{BaTi}{\mathrm{O}}_{3}$. We demonstrate that a composite specimen exhibiting merely \ensuremath{\sim}1% hexaferrite phase exhibits \ensuremath{\sim}34% increase in saturation polarization in a dc magnetic field of \ensuremath{\sim}10 kOe. Using modified Rayleigh analysis of the polarization field loop in the subcoercive field region we argue that the substantial enhancement in the ferroelectric switching is associated with the reduction in the barrier heights of the pinning centers of the ferroelectric-ferroelastic domain walls in the stress field generated by magnetostriction in the hexaferrite grains when the magnetic field is turned on. Our study proves that controlled precipitation of the magnetic phase is a good strategy for synthesis of 0-3 ferroelectric-ferromagnetic particulate multiferroic composite as it not only helps in ensuring a good electrical insulating character of the composite, enabling it to sustain high enough electric field for ferroelectric switching, but also the factors associated with the spontaneity of the precipitation process ensure efficient transfer of the magnetostrictive strain/stress to the surrounding ferroelectric matrix making domain wall motion easy.