Effects of Post-deposition Annealing on Epitaxial CoO/Fe3O4 Bilayers on SrTiO3(001) and Formation of Thin High-Quality Cobalt Ferrite-like Films

Abstract

In order to explore an alternative pathway to prepare ultrathin CoFe2O4 films, epitaxial CoO/Fe3O4 bilayers with varying film thickness of the CoO film were grown on Nb-doped SrTiO3(001) substrates via reactive molecular beam epitaxy. Thereafter, cobalt ferrite films with varying stoichiometry were prepared by post-deposition annealing at different temperatures. The thermally mediated interdiffusion resulted in the formation of vertical compressive and lateral tensile strained CoxFe3-xO4 films (x = 0.6 - 1.4) with homogeneous distribution of Fe and Co cations for each film. The chemical and electronic variations after each annealing step were studied by means of soft and hard X-ray photoelectron spectroscopy. The homogeneity of the cation distributions in the films were additionally verified after the last annealing step by angle-resolved hard X-ray photoelectron spectroscopy. For the cobalt ferrite film with x = 1.4, an additional crystallographic phase of Co1-yFeyO was observed by (grazing incidence) X-ray diffraction measurements after annealing at 600 degrees C. X-ray reflectivity measurements were performed to determine the film thickness of the formed CoxFe3-xO4 films.