Phase dependent room-temperature ferromagnetism of Fe-doped TiO2 nanorods

Fe-doped TiO2(B) and anatase phases were synthesized at different thermal treatment conditions using Fe-doped hydrogen titanate nanorods as a precursor. X-ray diffraction, Raman and Mössbauer studies ruled out the formation of secondary phase of either metallic Fe or iron oxide cluster in the samples and confirmed the ferromagnetism have originated from the defects. Mössbauer spectroscopy studies show a doublet and measured isomer shifts support the high spin Fe3+ charge state occupying the Ti4+ sites with associated changes in local lattice environment. The magnetization at room-temperature of the TiO2(B) sample is 0.020 emu/g whereas that of anatase sample is 0.015 emu/g. The decrease of magnetization with the structural phase transformation from TiO2(B) to anatase is attributed to the reduction in number of defects (oxygen vacancy) during the transformation process. Existence of these defects was further supported by the photoluminescence measurements.