X. H. Wang, J.-G. Li, H. Kamiyama, M. Katada, N. Ohashi, Y. Moriyoshi and T. Ishigaki. Pyrogenic Iron(III)-doped TiO2 nano- powders synthesized in RF thermal plasma: Phase formation, defect structure, band gap, and magnetic properties. Journal of Ameri-can Chemical Society, 2005, 127(31): 10982-10990.