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研究生:劉崇甫
研究生(外文):Liu, Chong-Fu
論文名稱:鐵磁體 Ce2Ru3(Ge1−????Si????)5、(La1−????Y????)5Co2Ge3 和Ni1−????Cu???? 的化學置換效應
論文名稱(外文):Chemical substitution effect on ferromagnets Ce2Ru3(Ge1−????Si????)5, (La1−????Y????)5Co2Ge3 and Ni1−????Cu????
指導教授:黃建龍黃建龍引用關係
指導教授(外文):Huang, Chien-Lung
口試委員:黃建龍陳威廷呂欽山楊弘敦
口試委員(外文):Huang, Chien-LungChen, Wei-TinLue, Chin-ShanYang, Hung-Duen
口試日期:2023-06-20
學位類別:碩士
校院名稱:國立成功大學
系所名稱:物理學系
學門:自然科學學門
學類:物理學類
論文種類:學術論文
論文出版年:2023
畢業學年度:111
語文別:中文
論文頁數:76
中文關鍵詞:鐵磁體化學置換古典臨界點量子臨界點
外文關鍵詞:ferromagnetchemical dopingclassical critical pointquantum critical point
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在凝態物理實驗中,化學置換是常見的調節工具之一,改變化學置換的濃度時會影響到系統的相變溫度。當相變溫度調變到絕對零度時,熱漲落的能量等於零,由另一種方式提供能量,被稱為量子漲落。事實上這兩種漲落同時提供相變所需的能量,但是熱漲落時通常勝過量子漲落的能量,因此大部分的研究是由熱漲落引發的相變。在量子臨界點的相關研究中大部分是反鐵磁系統,但很少有鐵磁系統的量子臨界點被發現。Ce2Ru3Ge5 和La5Co2Ge3 兩個結構都有非常低溫的鐵磁相變,居禮溫度分別在7.9 K和3.8 K。我們試圖使用矽置換鍺、釔置換鑭,只改變非磁性元素增加結構的無序性,降低其它變因的干擾,來達到鐵磁量子臨界點。對樣品分析後發現我們很難透過高溫電弧爐長出單一結構的Ce2Ru3Ge5 和La5Co2Ge3,時常伴有CeRu2Ge2 和LaCoGe3 以及其他未知結構。這些雜質中有一部份帶有磁有序,會讓臨界點的分析變得模糊不清難以繼續進行。此外我們也進行鎳銅合金Ni1−????Cu????的研究,並從熱漲落引起的相變開始討論,隨著摻雜量提升越接近量子臨界點時,臨界指數出現特別的變化,說明此系統將由熱漲落轉換成量子漲落。
In condensed matter physical experiments, chemical substitution is a common tool to modify the properties of systems. By altering the concentration of chemical substitutions, the phase transition temperature of the system can be influenced. When the phase transition temperature is adjusted to absolute zero, the energy from thermal fluctuations becomes zero, and an alternate form of energy known as quantum fluctuations takes over. In reality, both types of fluctuations provide the necessary energy for the phase transition. However, thermal fluctuations often overshadow the energy from quantum fluctuations, resulting in most research focusing on phase transitions induced by thermal fluctuations. Ce2Ru3Ge5 and La5Co2Ge3 exhibit very low-temperature ferromagnetic phase transitions, with Curie temperatures at 7.9 K and 3.8 K, respectively. Our aim is to achieve a ferromagnetic quantum critical point by substituting silicon for germanium and yttrium for lanthanum. This substitution alters only the non-magnetic elements, increasing the structural disorder and reducing interference from other variables. Upon analyzing the samples, we encountered difficulties in growing single-phase structures of Ce2Ru3Ge5 and La5Co2Ge3 using a hightemperature arc furnace. Often, impurities such as CeRu2Ge2, LaCoGe3, and other unknown structures were present. Some of these impurities exhibited magnetic order, making the nalysis of the critical point ambiguous and impeding further progress. We also studied nickel-copper alloys Ni1−????Cu????. As the doping level increases and approaches the quantum critical point, a notable change occurs in the critical exponents. This suggests a transition in the system’s behavior from being influenced primarily by thermal fluctuations to being dominated by quantum fluctuations.
中文摘要 I
Abstract II
誌謝 VII
目錄 VIII
表目錄 XI
圖目錄 XII
第一章緒論 1
1-1. 研究動機 1
1-2. 鐵磁體量子臨界點 2
第二章基礎理論 4
2-1. 相變理論 4
2-2. 臨界點 4
2-3. Arrott-Noakes理論 6
2-4. Hertz-Millis-Moriya理論 11
2-5. Belitz-Kirkpatrick-Vojta 理論 12
第三章實驗儀器 14
3-1. 高溫電弧爐 14
3-2. 管狀高溫爐 15
3-3. X-ray 繞射 16
3-4. 物理性質量測系統 17
3-4.1 電阻率量測 18
3-4.2 定壓熱容量量測 19
3-5. 磁性性質量測系統 21
3-5.1 震動樣品磁力計 21
3-5.2 約瑟夫森元件 22
第四章樣品製備與實驗分析結果 25
4-1. 鐵磁體Ce2Ru3(Ge1−xSix)5 的化學置換 25
4-1.1 Ce2Ru3Ge5 參考文獻 25
4-1.2 樣品製備 29
4-1.3 x-ray 繞射分析 30
4-1.4 磁性量測 33
4-1.5 電阻率量測 35
4-1.6 比熱量測 38
4-2. 鐵磁體La5Co2Ge3 的化學置換 39
4-2.1 La5Co2Ge3 參考文獻 39
4-2.2 樣品製備 42
4-2.3 x-ray 繞射分析 43
4-2.4 磁性量測 43
4-2.5 電阻率量測 48
4-2.6 比熱量測 49
4-2.7 單晶La5Co2Ge3 49
4-3. 鐵磁體Ni1−xCux 的化學置換 51
4-3.1 Ni參考文獻 51
4-3.2 樣品製備 52
4-3.3 高解析電子微探儀 53
4-3.4 x-ray 繞射 54
4-3.5 磁性量測 56
4-3.6 臨界指數 61
第五章結論 70
5-1. 鐵磁體Ce2Ru3(Ge1−xSix)5 的化學置換 70
5-2. 鐵磁體La5Co2Ge3 的化學置換 70
5-3. 鐵磁體Ni1−xCux 的化學置換 71
參考文獻 72
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