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We report here the unexpected observation of significant room-temperature ferromagnetism in a semiconductor doped with nonmagnetic impurities, Cu-doped TiO 2 thin films grown by pulsed laser deposition. The magnetic moment, calculated from the magnetization curves, resulted surprisingly large, about 1.5 B per Cu atom. A large magnetic moment was also obtained from ab initio calculations, but only if an oxygen vacancy in the nearest-neighbor shell of Cu was present. This result suggests that the role of oxygen vacancies is crucial for the appearance of ferromagnetism. The calculations also predict that Cu doping favors the formation of oxygen vacancies.

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We present an investigation of Fe-doped TiO2 anatase nanoparticles (2.8 and 5.4 at.% Fe) where Fe substitutes Ti atoms without the presence of other phases. In order to characterize these samples we used x-ray absorption experiments, 57Fe Mössbauer spectroscopy, ab initio calculations and magnetometry. Results from iron K-edge near-edge and extended x-ray absorption fine structure confirm that Fe3+ replaces Ti4+ in the TiO2 anatase structure increasing the metal-anion bond length. Mössbauer spectra recorded at room temperature show asymmetric Fe3+ broad doublets. These results agree with structural, hyperfine and magnetic properties calculated using density-functional theory, if oxygen vacancies are present in the iron–oxygen octahedra. Mössbauer and magnetic measurements indicate that samples are paramagnetic at room temperature. At low temperatures, two kind of magnetic species can be distinguished: (i) isolated paramagnetic Fe3+ ions and (ii) antiferromagnetically coupled Fe3+ ions. These results also show that substitutional Fe in nanosized anatase TiO2 does not induce ferromagnetic ordering.