Oxygen vacancy induced room temperature ferromagnetism in Pr-doped CeO₂ thin films on silicon

Integration of functional oxides on Si substrates could open a pathway to integrate diverse devices on Si-based technology. Oxygen vacancies (Vo) can strongly affect solid state properties of oxides, including the room temperature ferromagnetism (RTFM) in diluted magnetic oxides. Here, we report a systematical study on the RTFM of oxygen vacancy engineered (by Pr³⁺ doping) CeO₂ epitaxial thin films on Si substrates. High quality, mixed single crystalline Ce_1-xPr_xO_2-δ (x = 0-1) solid solution films were obtained. The Ce ions in CeO₂ with a fluorite structure show a Ce⁴⁺-dominant valence state in all films. The local crystal structures of the films were analyzed in detail. Pr doping creates both Vo and PrO₈-complex defects in CeO₂ and their relative concentrations vary with the Pr-doping level. The RTFM properties of the films reveal a strong dependence on the relative Vo concentration. The RTFM in the films initially increases with higher Pr-doping levels due to the increase of the F⁺ center (Vo with one occupied electron) concentration and completely disappears when x > 0.2, where the magnetic polaron concentration is considered to decline below the percolation threshold, thus long-range FM order can no longer be established. We thus demonstrate the possibility to directly grow RTFM Pr-doped CeO₂ films on Si substrates, which can be an interesting candidate for potential magneto-optic or spintronic device applications.