Effects of depositing rate on structure and magnetic properties of Mn:TiO2 films grown by plasma-assisted molecular beam epitaxy

We research the relationship between structural quality and magnetic ordering, using epitaxial Mn-doped anatase TiO2 with excellent structural quality as a model system. Epitaxial films deposited slowly 0.08 (Å/s) possess a perfect crystalline structure, whereas films deposited at 0.2 (Å/s) are found to have a highly defected crystalline structure, as characterized by X-ray diffraction (XRD). X-ray photoelectron spectroscopy studies (XPS) indicate the possibility of hybridization between the Mn2+ ions and host defects. In contrast to defective Mn:TiO2, these structurally superior films show negligible magnetism. It is demonstrated that room temperature ferromagnetism strongly correlated with the defect density of the sample.