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.