Regulation of defect complexes at the interface for improving multiferroicity of Bi0.79La0.18Sr0.03Fe0.94Mn0.04Co0.02O3/CoFe2-xLaxO4 bilayer thin films

Abstract

This work presents the Bi0.79La0.18Sr0.03Fe0.94Mn0.04Co0.02O3/CoFe2-xLaxO4 (BLSFMC/CFLxO) multiferroic bilayer films with Au top electrode on the fluorine doped tin oxide (FTO) by sol-gel method. And the change in structure and properties of BLSFMC/CFLxO films are investigated. The results show that the upper layer of BLSFMC is induced structural distortion by doping La3+ in the underlying CFO and the R3m: R structural phase content increases. La3+ blocks the diffusion of Fe2+ ions into the BLSFMC layers, reduces the oxygen vacancies concentration, and weakens the valence fluctuations of Fe, Mn, and Co ions in the upper BLSFMC layer, decreasing the number of defect complexes and improving the insulation properties of the BLSFMC/CFLxO bilayer. The pinned ferroelectric domain at the BSLFMC/CFL0.03O interface is reduced, and the ferroelectricity of the BLSFMC layer is released. The residual polarization of BLSFMC/CFL0.03O Pr = 136.82 μC/cm2, the squareness ratio Rsq = 1.20 and the saturation magnetization Ms = 90 emu/cm3 compared with the single-phase BLSFMC thin films, BLSFMC/CFL0.03O bilayer thin films exhibits excellent ferroelectricity and has a large amount of enhanced ferromagnetism. The structure and multiferroicity properties of the bilayer films can be adjusted by the underlying La3+ dopant.