Anatase and rutile TiO2-δ powders were synthesized via the sol-gel method. The

hysteresis loops and the zero field-cooled and the field-cooled magnetization

curves indicate that reduced TiO2-δ powders exhibit the room-temperature

ferromagnetism that becomes stronger with prolonging annealing time in H2/Ar

mixture. Analysis of Ti 2p X-ray photoelectron spectroscopy spectra indicates that

Ti ions were all in the Ti4+ state and that Ti3+ or Ti2+ ions do not exist in all

samples. In addition, analysis of O 1s X-ray photo-electron spectroscopy spectra

indicates that the concentration of oxygen vacancies increases with prolonging

annealing time. Analysis of ultraviolet-visible absorption spectra also further

confirmed that the concentration of oxygen vacancies increases with prolonging

annealing time. These results indicate that ferromagnetism in pure TiO2-δ powders

stems from oxygen vacancies.

Activation of Room-Temperature Ferromagnetism in Non-Stoichiometric TiO2-δ

Powders by Oxygen Vacancies. Q.Zhao, P.Wu, B.L.Li, Z.M.Lu, E.Y.Jiang: Journal

of Applied Physics, 2008, 104[7], 073911