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We studied the structural, chemical and magnetic properties of non-doped ceria (CeO(2)) thin films electrodeposited on silicon substrates. Experimental results confirm that the observed room temperature ferromagnetism is driven by both cerium and oxygen vacancies. We investigated ceria films presenting vacancy concentrations well above the percolation limit. Irradiation experiments with neon ions were employed to generate highly oxygen defective CeO(2-δ) structures. X-ray photoelectron spectroscopy and x-ray absorption near-edge structure spectroscopy were used to estimate the concentration of Ce(3+) sites in the films, which can reach up to 50% of Ce(3+) replacing Ce(4+), compared to a stoichiometric CeO(2) structure. Despite the increment of structural disorder, we observe that the saturation magnetization continuously increases with Ce(3+) concentration. Our experiments demonstrate that the ferromagnetism observed in ceria thin films, highly disordered and oxygen-deficient, preserving the fluorite-type structure only in a nanometer scale, remains intrinsically stable at room temperature.

The structural and magnetic properties of MnAs epilayers grown on GaAs͑111͒B have been investigated by x-ray diffraction and magnetometry. The strain evolution of the epilayer was followed during the phase transition by x-ray diffraction. The results show a high fraction of the ␣ ferromagnetic phase at room temperature and an elevated value of the structural phase transition temperature. The system is strongly affected by residual strains that are mainly located inside the ␤ phase. We attribute this behavior to an increase in the elastic energy density associated with the tight link between epilayer and substrate. It comes out that magnetic and structural properties of MnAs thin films are strongly dependent on the crystallographic relation between epilayer and substrate.

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