Ferromagnetism of Co-doped TiO2 films prepared by plasma enhanced chemical vapour deposition (PECVD) method

Ti1-xCoxO2 polycrystalline films have been prepared on Si(0 0 1) substrates by the plasma enhanced chemical vapour deposition technique at 280 degrees C without using any carrier gas. All the films show room-temperature ferromagnetic behaviours and no ferromagnetic clusters are detected by x-ray diffraction, x-ray photoelectron spectroscopy, atomic force microscopy, Raman and superconducting quantum interference device measurements as the doping concentration is lower than 4%. In addition, the formation of non-ferromagnetic CoTiO3 under heavy doping is considered to be responsible for the degradation of magnetization in Ti1-xCoxO2 polycrystalline films. Furthermore, saturated magnetization of Ti1-xCoxO2 films is found to decrease with the increasing duration of oxygen-plasma processing, indicating that the oxygen vacancies in the films play an important role in the generation of ferromagnetic Ti1-xCoxO2 films.