Direct evidence of oxygen vacancy mediated ferromagnetism of Co doped CeO2thin films on Al2O3(0001) substrates

Thin films of room temperature diluted magnetic oxides (DMO) of Co doped CeO 2 (Ce 0.97 Co 0.03 O 2−δ ) with a predominant orientation of (001) have been deposited on Al 2 O 3 (0001) substrates. An Ar + sputtering process has been applied to the as deposited films to investigate its effect on the films' ferromagnetic properties. With the aid of magnetic measurements, we find that Ar + bombardment has an obvious effect on the magnetic properties of the as deposited films, i.e., the saturated magnetization moments ( M S ) are enhanced by Ar + bombardment. More detailed work has been done to further explore the inherent mechanism. Ar + sputtering was found to introduce additional oxygen vacancies (V O ) into the as deposited films (through x-ray photoelectron spectroscopy and Raman spectral analysis), which should make a certain contribution to the enhanced M S observed for Ar + sputtered films. The experimental results provide direct evidence of V O enhanced ferromagnetism of insulating DMO, and are consistent with the recently proposed F-center exchange coupling mechanism.