本研究利用X光吸收光譜(XAS)分析經過不同製程（熱裂解法、沈澱法）、不同退火處理（Air, Ar+H2）、以及摻雜不同濃度Fe離子之CeO2奈米粉末中Ce及Fe離子價數的變化，配合XRD以及SQUID分析結果，探討氧空缺及所摻雜磁性元素之價數對氧化物(metal-oxides)室溫鐵磁性的影響。
實驗結果發現，與沈澱法相比，以熱裂解法合成之粉末其氧空缺數量與Ce3+含量較高，但磁性量測結果則顯示以熱裂解法合成之樣品並沒有室溫鐵磁特性，因此，我們推測過多的氧空缺將使室溫鐵磁性下降甚至消失。進一步將熱裂解法合成的粉末在Air下退火，氧空缺數量以及Ce3+含量隨著退火時間增加而逐漸減少，樣品又產生室溫鐵磁性。而以沈澱法合成之粉末在Ar+H2下退火，隨著退火時間增加，氧空缺數量以及Ce3+含量則逐漸上升，飽和磁化強度也隨之變大。
而在摻雜Fe的樣品，XAS結果顯示Fe為三價的型態存在，並以Fe3+-Vo-Fe3+的型態存在於CeO2中。由Ce與Fe的價數變化分析結果，我們推測摻雜Fe的CeO2奈米顆粒之鐵磁為雙交換與FCE機制共同作用的結果。

In order to reveal the effect of oxygen vacancy（Vo） and the valance of dopant on room temperature ferromagnetism（RTFM）in Cerium dioxide（CeO2） nanoparticles, X-ray absorption spectroscopy (XAS) was used in this study to analyze the valance of Ce and Fe ions of CeO2 nanoparticles prepared by using different process (thermal decomposition and precipitation), undergo different annealing process (in air or reducing condition), and doping with different amount of Fe ions.
XAS results show that the concentration of Vo and Ce3+ both higher in CeO2 samples prepared by using thermal decomposition method than using precipitation. However, the former one is not ferromagnetism at room temperature. It is thus supposed that ferromagnetism will be suppressed of samples with too high degree oxygen deficiency. The relationship between oxygen deficiency and ferromagnetism was then build up by measuring the valance of Ce of CeO2 nanoparticles undergo different annealing process.
On the other hand, for CeO2 nanoparticles doping with Fe ions, XAS analysis indicated that Fe is trivalent. EXAFS analysis implied the formation of Fe3+-Vo-Fe3+. At last, according to the analysis of the valance of Fe and Ce, we suggested that ferromagnetism of Fe doped CeO2 nanoparticles is contributed both by double exchange and FCE mechanism.

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