臺灣博碩士論文加值系統

Ce3Al11塊材在溫度6.2K時有一鐵磁性相變，當溫度於3.2K時出現反鐵磁性相變。文獻記載[1]當尺寸縮小時Ce3+濃度有減少的傾向，本實驗試圖探討當無序性(disorder)存在樣品時，對樣品磁性性質的影響，以釐清無序性對奈米樣品的磁性性質改變所扮演的角色。利用傳統球磨機製作出Ce3Al11的微粒，微粒樣品製作完成後，利用X光繞射儀鑑定成份與結構是否與母材相同。寬化的X光繞射峰顯示明顯的無序性已藉由球磨過程引入樣品中。利用HR-TEM 觀察樣品型態並獲得粒徑分佈，顯示樣品形狀非常不規則，其大小約338 ± 263 nm。透過SQUID的量測與比熱的分析結果將與相關文獻作比較。我們發現球磨樣品反鐵磁性被壓抑，這現象與雷射製作的樣品類似，並且樣品在溫度6 K 下呈現超順磁行為。藉由比較不同尺寸與製程獲得的樣品，可發現無序性與尺寸效應將壓抑磁性相變。當尺寸進入奈米級時，康斗(Kondo)行為明顯出現在比熱的溫度關係圖。所有的非塊材樣品，均呈現具磁矩的Ce3+有減少的趨勢，當樣品尺寸越小此趨勢越明顯。

The bulk CeAl4 undergoes a ferromagnetic transition at TC = 6.2K , follow by an antiferromagnetic ordering at TN = 3.2K . Some studies were reported that when the size of Ce3Al11reduce , the concentration of Ce3+ decrease . In order to investigate the influence of disorder on small particles, the Ce3Al11 small particles was fabricated by ball-milling method . X-ray diffraction (XRD),high resolution transmission electron microscopy (HR-TEM) and scanning electron microscopy (SEM) , were used to analyze the structure and the sizes of these particles . The sizes of ball-milling samples were about 338 ± 263 nm . We find that the antiferromagnetism of particles fabricated by ball-milling were suppressed ,which is similar with the nanoparticles fabricated by pulse laser deposition . A typical behaviors of superparamagnetism exhibited on the χ-T curve below 6K ,imply that the samples remain on ferromagnetic state between 2K and 6K . The smaller curie constant obtained from ball-milling samples was about 78% of the bulk .The reduce of Ce3+ is similar to the samples fabricated by sputtering method and pulse-laser ablation . By the calorimetric measurements , we find that the ferromagnetic and the antiferromagnetic transitions still exist in BM-sample .The entropy calculated from specific heat show that the decrease of Ce3+ in all samples with size blow sub-micrometer.

第一章 導論 ..............................................1
第二章 實驗理論
§ 2-1 物質磁性............................................4
§ 2-2 稀土族元素磁性......................................7
§ 2-3 磁交互作用..........................................7
§ 2-4 混合價鍵............................................9
§ 2-5 重費米子系統.......................................10
§ 2-6 奈米微粒一般特性...................................11

第三章 樣品的製作與儀器原理
§ 3-1 塊材製備...........................................16
§ 3-2 Nd-YAG Q-Switch脈衝雷射簡介........................18
§ 3-3 熱蒸鍍法與球磨法...................................25
§ 3-4 X-RAY Diffraction 原理概述..........................27
§ 3-5 SEM(掃描電子顯微鏡)原理與結構......................29
§ 3-6 TEM(穿透式電子顯微鏡)原理與結構....................33
§ 3-7 He3比熱量測.........................................37
§ 3-8 超導量子干涉磁量儀(SQUID)磁化率的量測..............45

第四張 結果與討論
§ 4-1 XRD與成分鑑定......................................51
§ 4-2球磨粒徑大小分......................................57
§ 4-3磁性行為............................................64
§ 4-4比熱量測............................................72
§ 4-5 結論...............................................80

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