Abstract
In this research, the origin of magnetism in diluted magnetic oxides system has been investigated using a variety of different experimental methods. Cobalt doped cerium oxide nanoparticles were synthesized by chemical precipitation technique. It is possible to adjust the concentration of oxygen vacancies through oxygen or forming gas thermal annealing. The precursor ratio changes the concentration of cobalt dopant atoms. We have studied the correlation between magnetism and oxygen vacancies or concentration of doping cobalt in this DMO system. The long-range-order cerium oxide structure was investigated by X-ray diffraction (XRD). High resolution transmission electron microscopy (HRTEM) was used to obtain the images of cerium oxide nanoparticles. The result of cobalt K-edge x-ray absorption near-edge structure(XANES) ruled out the possibility of forming cobalt oxide or cobalt clusters. Extended x-ray absorption fine structure (EXAFS) measurements not only reveal the cobalt short-range-order structure but also confirm that cobalt atoms are on interstitial sites in the CeO2 host. Raman spectra provide the evidence that the concentration of oxygen vacancies increase after annealing in forming gas. The room temperature M-H curve reveals paramagnetism in all samples, and ferromagnetism in some oxygen vacancy rich samples, which implies an important correlation between oxygen vacancies, cobalt doping and ferromagnetism. Finally, the bounded magnetic polarons model was supported by our results to be responsible for the magnetism in cobalt doped cerium oxide nanoparticles.