Microstructure and ferroic properties of epitaxial [γ-Fe2O3–BiFeO3]−Bi3.25La0.75Ti3O12 composite bilayers

Epitaxial [γ-Fe2O3–BiFeO3]/Bi3.25La0.75Ti3O12 and Bi3.25La0.75Ti3O12/[γ-Fe2O3–BiFeO3] composite bilayers were grown on SrRuO3 coated (111) SrTiO3 substrates in order to investigate the influence of the morphology of the γ-Fe2O3–BiFeO3 self assembled nanocomposite layer on the multiferroic properties of the bilayer. Both types of bilayers exhibit high resistivity and simultaneously ferroelectricity and ferrimagnetism at room temperature. When the γ-Fe2O3–BiFeO3 composite layer is sandwiched between the Bi3.25La0.75Ti3O12 film and the substrate, the BiFeO3 component is not only subjected to epitaxial strain induced by the surface on top of which it grows but also to elastic interactions with the Bi3.25La0.75Ti3O12 capping layer. The latter indeed reduce the amount of γ-Fe2O3 inclusions, affects the morphology of the grains in the γ-Fe2O3–BiFeO3 layer, and increases the shape anisotropy of the γ-Fe2O3 inclusions. Additionally, this modification in the microstructure of the γ-Fe2O3–BiFeO3 layer induces an imprint in the ferroelectric hysteresis loop as well as a decrease in the saturation magnetization, and its magnetic easy axis direction changes from in-plane to out-of plane.