In this thesis, we have studied the correlation between magnetism and oxygen vacancies in yttrium oxide based diluted magnetic oxide (DMO) systems. Yttrium oxide nanoparticles (NPs) doped with 3d transition metals (TM) cobalt and manganese are synthesized by thermal decomposition of yttrium acetylacetonate (Y(acac)3) in oleylamine. Thermal annealing in either oxygen or forming gas was employed to adjust the concentration of oxygen vacancies. The nanoparticles' size and structures of the Y2O3 host were investigated by x-ray powder diffraction (XRD) and high resolution transmission electron microscopy (HR-TEM). Cobalt and manganese K-edge x-ray absorption near-edge structure (XANES) spectra were used to determine the oxidation state of the dopant atoms. Local environments surrounding Co and Mn were probed by using extended x-ray absorption fine structure (EXAFS) techniques. Both Co and Mn impurity atoms were found to locate on interstitial sites with O nearest neighbors and shorter TM-O bond as compared to the Y-O bond in the Y2O3 host. Forming gas (5%H2/95%N2) annealing has significantly increased the concentration of the oxygen vacancies while oxygen gas annealing has decreased the oxygen vacancies in all samples. As revealed by SQUID measurements performed at temperatures 10K and 300K, the Co- and Mn-doped samples show combinations of ferromagnetism and paramagnetism while an undoped sample is diamagnetic. This indicates that the observed ferromagnetism is indeed due to the doping of transition-metal atoms in the samples. Our experimental results on the correlation between oxygen vacancies and magnetism appear to be rather consistent with the bound magnetic polaron model.
章節目錄
摘要
誌謝
章節目錄
圖表目錄
第一章 序論
1-1-1-研究動機
1-2-1-論文簡介
第二章 理論與文獻回顧
2-1-1-高介電係數 (High-k material) 氧化物簡介
2-2-1-稀磁性氧化物(DMOs ; Diluted magnetic oxides)簡介
2-3-1-DMOs磁性來源理論簡介
2-3-1-Bound magnetic polarons (BMPs)
2-3-2-Charge-transfer ferromagnetism
2-4-1-三氧化二釔(Y2O3 ; yttrium oxide)材料簡介
第三章 實驗方法與原理
3-1-1-X光繞射儀(X-ray diffractometer)
3-2-1-高解析穿透式電子顯微鏡(HRTEM)
3-3-1-超導量子干涉儀(SQUID)
3-4-1-感應耦合電漿質譜分析儀(ICP-MS)
3-5-1-X光精密吸收光譜(XAFS)
第四章 實驗結果與分析
4-1-1-熱分解法(Thermal decomposition method)合成奈米粒子
4-1-1-實驗試藥
4-1-2-實驗流程圖
4-1-3-油相熱分解法製備過渡金屬攙雜之氧化釔奈米粒子
4-1-4-氣氛退火
4-2-1-X光繞射分析(XRD)分析
4-3-1-高解析穿透式電子顯微鏡(HRTEM)分析
4-4-1-X光精密吸收結構(XAFS)分析
4-4-1近邊X光精密吸收結構 (XANES)
4-4-2延伸X光精密吸收結構 (EXAFS)
4-4-2-1鈷攙雜之氧化釔奈米粒子之EXAFS分析
4-4-2-2錳攙雜之氧化釔奈米粒子之EXAFS分析
4-5-1-磁性分析
第五章 結論
5-1-1-總結
5-2-1-未來展望
參考文獻
參考文獻
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