Room temperature ferromagnetism in spin-coated anatase- and rutile-Ti0.95Fe0.05O2 films

Thin films of Ti1−xFexO2 (x = 0 and 0.05) have been prepared on sapphire substrates by the spin-on technique starting from metal–organic precursors. When heat treated in air at 550 and 700 °C respectively, these films present pure anatase and rutile structures as shown both by x-ray diffraction and Raman spectroscopy. Optical absorption indicates a high degree of transparency in the visible region. Such films show a very small magnetic moment at 300 K. However, when the anatase and the rutile films are annealed in a vacuum of 1 × 10−5 Torr at 500 and 600 °C respectively, the magnetic moment, at 300 K, is strongly enhanced, reaching 0.46 μB/Fe for the anatase sample and 0.48 μB/Fe for the rutile one. The ferromagnetic Curie temperature of these samples is above 350 K. When the ferromagnetic rutile sample is reheated in air, the magnetic moment reduces strongly. The data seem to indicate that oxygen defects created as a result of vacuum annealing may be responsible for the observed ferromagnetism in our samples.