Chemistry of post-annealing of epitaxial CoFe2O4 thin films

CoFe2O4 thin films of different thicknesses were grown on SrTiO3 substrates. The X-ray diffraction analysis and atomic force microscopy indicated both epitaxy and a granular microstructure. We studied the magnetic properties of these films as a function of oxygen post-annealing and film thickness. All as-deposited films exhibited similar magnetic properties with saturated magnetization (Ms) of approximately 50% of the bulk Ms, (80 Am2 kg− 1). After the post-annealing the Ms changes as a consequence of crystallographic restructuring of the film. Cation ordering in 100 nm thick films reduces Ms, whereas re-oxidation increases Ms for thinner films. 13 nm films, annealed for 1 h, reach the bulk Ms. For even thinner films the quantum-size effect reduces Ms. For a synthesis of ≥ 30 nm films an annealing cycle after deposition of every 15 nm layer is recommended.