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 700degreesC 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 I x 10(-5) Torr at 500 and 600degreesC respectively, the magnetic moment, at 300 K, is strongly enhanced, reaching 0.46 mu(B)/Fe for the anatase sample and 0.48 mu(B)/Fe for the rutile one. The ferromagnetic Curie temperature of these samples is above 350 K. When the ferromagnetic rutile sample is reheated in P 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.