本研究利用沉澱法製備CeO2 奈米顆粒，首先利用改變合成過程中的沉澱劑(NH4OH) 濃度，控制樣品之粒徑大小，結果發現同時會影響合成顆粒中的Ce3+ 比例。進一步將合成的樣品在還原氣氛 (97%Ar+3%H2) 下，進行一小時到五小時的退火處理，溫度為300oC，再利用XAS吸收光譜分析 Ce的價數變化，搭配磁性量測的結果及粒徑分析，結果發現此還原步驟使樣品中的氧空缺數量增加，且氧空缺較傾向形成在表面；值得注意的是，實驗結果顯示，樣品的飽和磁化強度與樣品中所含的Ce3+ 數量並非成正比，由實驗結果並可推測，當表面的Ce3+ 比例達到約 35%，會有最大的飽和磁化強度 (MS)。另一方面，經由 MCD的分析，我們推測氧確實在磁性產生的過程中扮演相當重要的角色。
另外，為探討摻雜磁性元素對 CeO2 樣品鐵磁性來源之影響，摻雜不同濃度之鐵離子到 CeO2 顆粒中，並進一步將摻雜鐵離子之樣品做氧化還原處理。由 XAS及磁性分析結果，除了建立摻雜量與飽和磁化強度之關係外，並進一步發現摻雜鐵離子之CeO2 奈米顆粒其磁性產生來源有二，一為顆粒表面的氧空缺，另一為所摻雜的鐵離子。本實驗結果將可利用作為後續製備高磁化強度之 CeO2材料之參考。

In order to study the effect of size, oxygen vacancy, and dopant on the ferromagnetism, in this study, CeO2 nanoparticles doping with iron (Fe) were synthesized by using precipitation method and then annealed in Ar +3% H2 at 300oC for 1 to 5 hours. The doping level of Fe ranges from 0 to 11 at%. The results show that the concentration of Ce3+ of nanoparticles varies with the pH value of precursor. XAS analysis and magnetic measurements results find that the concentration of Ce3+ increase with increasing the annealing time. In addition, it is predicted that Ce3+ tends to segregate at the surface of nanoparticles. The concentration dependence of oxygen vacancy on the ferromagnetism was also build up in this study. The saturation moment (Ms) is not proportional to the concentration of Ce3+. The highest Ms value was found in sample of which the concentration of Ce3+ is about 35 %.
At last, the relationship between doping level of Fe and the value of Ms of CeO2 nanoparticles was build up. According to the XAS and magnetic measurement results, it is indicated that the ferromagnetism of Fe doped CeO2 nanoparticles was contributed by two origins. One is the oxygen vacancy and Ce3+ at surface, the other is the oxygen vacancy and Fe3+ in the inner part of particles. The results of this study can be used to prepare CeO2 materials with high Ms values in the future.

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