Direct evidence of oxygen vacancy mediated ferromagnetism of Co doped CeO2 thin films on Al2O3(0001) substrates

Thin films of room temperature diluted magnetic oxides (DMO) of Co doped CeO2 (Ce0.97Co0.03O2−δ) with a predominant orientation of (001) have been deposited on Al2O3(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 (MS) 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 (VO) into the as deposited films (through x-ray photoelectron spectroscopy and Raman spectral analysis), which should make a certain contribution to the enhanced MS observed for Ar+ sputtered films. The experimental results provide direct evidence of VO enhanced ferromagnetism of insulating DMO, and are consistent with the recently proposed F-center exchange coupling mechanism.

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