我們藉由溶膠凝膠法在700℃以及更高溫度合成0.5%莫耳濃度，氧化銪參雜於二氧化矽基底之奈米粒子複合物，並且對其做了X-ray、TEM、磁性和介電係數等實驗。由X-ray 和TEM 研究得知此一複合物的粒子大小介於4-8 奈米之間，且粒子大小隨合成溫度升高而增大。磁性對溫度以及磁滯曲線的研究中，此一複合物展現了超順磁相。介電係數的研究中顯示高介電係數值，並且在介電係數對溫度的關係圖中，於270 K 展現出寬廣的峰值是為擴散相變。磁電偶合實驗中，此一系統顯現出負的磁介電效應，在9 T 的磁場下2.5 kHz 時介電常數降低約為零場1.5 倍，推測是由於磁場影響奈米粒子的電阻造成的磁阻效應造成的，此現象會由於改變參雜的粒子大小而產生改變。我們推測這些現象的成因是由於化合物的氧空缺之熱效應造成的。這種高介電係數並展現出磁介電效應材料在將來應用上有相當大的潛力。

Magnetic nanocrystalline Eu2O3 (0.5 mol %) particles have been synthesized in a silica glass matrix by the sol-gel method at calcination temperatures of 700oC and above. X-ray and TEM studies reveal the nanocrystals with mean sizes in the range 4–8 nm, larger in the samples calcined at higher temperatures. The magnetization and magnetic hysteresis of Eu2O3 nanocrystals in the temperature range of 2-300K have demonstrated that the Eu2O3 nanocrystals in these glasses display superparamagnetic state. The temperature dependence of dielectric constant curves demonstrate a broad maximum around Tm ~ 270 K characteristic by diffuse phase transition (DPT). At the highest applied magnetic field 9 tesla, at superparamagnetic phase, the dielectric constant around Tm decreases almost ~ 1.5 (at 2.5 kHz) times compared with that at zero field for the sample calcined at 700℃ (~2 nm). The magnetodielectric effect observed in the glass composite is considered to be affected with the direct consequence of magnetoresistance changes which depends on the magnetic nanoparticle size and separation. Combustion mechanism is closely relate to the thermally activation oxygen vacancy. Such a material might be treated as a potential candidate for device miniaturization.

Content
Abstract……………………………………………………………………………3
論文摘要…………………………………………………………………………4
Content……………………………………………………………………………5
List of figures……………………………………………………………………7
List of tables……………………………………………………………………9
Chapter 1: Introduction……………………………………………………10
1.1 General introduction …………………………………………………10
1.2 Motivation………………………………………………………………12
1.3 Magnetic and dielectric property of materials…………………14
1.3.1 A Brief Resume on the Magnetism of Nano-magnetic Materials14
1.3.2 Dielectric property………………………………………………22
Chapter 2: Experimental methods and instrumentation……31
2.1 Sample preparation…………………………………………………31
2.1.1 Physical methods…………………………………………………31
2.1.2 Chemical methods………………………………………………33
2.2 XRD and TEM measurements…………………………………37
2.2.1 XRD measurements…………………………………………………37
2.2.2 TEM measurements………………………………………………40
2.3 Magnetic measurements……………………………………………44
2.3.1 Zero-field-cooled magnetization (MZFC) measurements………47
2.3.2 Field-cooled magnetization (MFC) measurements…………………49
2.3.3 Hysteresis measurements……………………………………50
2.4 Dielectric measurements……………………………………………51
Chapter 3: Results and discussion……………………………………54
3.1 Sample characterization by TEM and XRD……………………54
3.2 Magnetic properties…………………………………………………57
3.3 Dielectric properties…………………………………………………61
Chapter 4: Conclusion……………………………………………………69
References………………………………………………………………………70

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