Fe-doped TiO_2 rutile thin films were fabricated by reactive magnetron sputtering on SiO_2 substrates under different growth conditions, and the structure and magnetism have been systematically investigated. X-ray diffraction data, atomic force microscopy, and magnetic force microscopy confirm the absence of metallic Fe clusters or any other impurity phase. The divalent Fe ion was identified by x-ray photoelectron spectra. Room-temperature ferromagnetism has been observed for all the Fe_xTi_(1-x)O_2 (x=3%-15%) rutile films. However, the saturation magnetization (M_s) varied drastically for different pressures, doping concentrations, and annealing processes. The results show that ferromagnetism originates from the doped matrix rather than any type of magnetic cluster and the ferromagnetism is strongly correlated with the oxygen vacancies in TiO_2.
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