Magnetism of Co-doped titania thin films prepared by spray pyrolysis

Co-doped TiO2 (anatase) films prepared by spray pyrolysis at 500degreesC are investigated for the possible existence of room temperature ferromagnetism (RTF). These films were characterized by x-ray diffraction, Raman spectroscopy, and x-ray photoelectron spectroscopy at room temperature, followed by studies of the temperature and magnetic field dependence of the magnetization by squid magnetometry. For Co doping of upto 10 at. %, no phase other than anatase could be detected, and there is no RTF in these films. Instead, the magnetic susceptibility chi fits the modified Curie-Weiss law chi=chi(0) + C/(T + theta), with theta similar or equal to 5 K and magnitude of C consistent with Co2+ paramagnetism in Ti1-xCoxO2-x. Only for T less than or equal to 5 K, a hysteresis loop with coercivity H-c = 200 Oe is observed. These observations suggest Co2+ paramagnetism, with exchange interaction becoming important for T less than or equal to 5 K in the case of 10% Co/TiO2 films. (C) 2003 American Institute of Physics.