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研究生:方德翰
研究生(外文):De-Han Fang
論文名稱:超導體LaAg1−cMnc(c=0.1~0.7)的物理特性
論文名稱(外文):The Physical Property Of Superconductor LaAg1−cMnc(c=0.1~0.7)
指導教授:藍明德
指導教授(外文):Ming-De Lan
口試委員:陳坤麟李文新
口試日期:2017-07-14
學位類別:碩士
校院名稱:國立中興大學
系所名稱:物理學系所
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:2017
畢業學年度:105
語文別:中文
論文頁數:50
中文關鍵詞:超導體BCS理論反鐵磁自旋擾動
外文關鍵詞:superconductorBCS theoryAntiferromagnetic-spin-fluctuation
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本研究的母體材料LaAg是一種合金材料,其中La帶有磁性,LaAg超導臨界溫度為0.9 K。經過摻雜另一種磁性元素Mn以取代LaAg晶格中Ag的位置,製成化學式為LaAg1−cMnc的晶體(摻雜範圍為c=0.1~0.7)。樣品燒結使用的是電弧爐氬焊法。量測方面使用到X-Ray粉末繞射儀(XRD)、超導量子干涉儀(SQUID),以進行各種物理分析。並對不同比例摻雜後在溫度為2 K到300 K的範圍以及不同的外加磁場之下觀察,發現磁滯曲線和超導臨界溫度有了令人值得探討的改變。

LaAg1−cMnc其元素組成皆為過渡元素與稀土元素,對於此非傳統超導其古柏電子對(Cooper pair)的形成機制和存在狀態是否和BCS理論敘述的狀態一模一樣﹖或是因反鐵磁自旋擾動(Antiferromagnetic-spin-fluctuation)才促使古柏電子對的形成,也是一個值得討論以及待驗證的議題!
The binary compound of LaAg in this study has superconducting critical temperature 0.9 K. A serious of LaAg1-cMnc (c = 0.1 ~ 0.7) compounds were made by arc-melt argon welding method. The quality of the specimen is characterized by X-Ray powder diffractometer (XRD). The superconducting behavior and magnetic hysteresis were measured by Superconducting Quantum Interference Device (SQUID) over wide temperature region of 2 K to 300 K under various applied magnetic fields. It is found that the superconducting critical temperature has extremely fascinating change.
There is a relatively high superconducting critical temperature Tc = 5.7 K for the c = 0.1 specimen, and the hysteresis curve shows a superconducting loop with a paramagnetic background.
There are rare-earth element La and transition-metal element Mn in the three dimensional LaAg1−cMnc system, both of them own the magnetic moment. According to the BCS theory, the superconductivity cannot occur under this magnetic background. For such an unconventional superconductor it is worthy to discuss the formation mechanism of superconducting pairs. An antiferromagnetic-spin-fluctuation model was proposed to be the formation mechanism of Cooper electronic pairs in these LaAg1-cMnc compounds
致謝 i
摘要 ii
Abstract iii
目次 iv
表目錄 vi
圖目錄 vii
第一章 簡介 1
1-1超導體簡介 1
1-2 BCS理論 3
1-3 倫敦穿透深度(London penetration depth) 5
1-4 物質的磁性 7
1-5居禮定律(Curie Law) 12
1-6晶格場作用(Crystalline electric field effect) 15
1-7 近藤效應(Kondo effect) 16
第二章 樣品製備與分析方法 19
2-1樣品製備 19
2-2 樣品分析 22
2-2.1結構量測 X-Ray粉末繞射儀( X-Ray Diffractometer,XRD) 22
2-2.2表面量測 掃描式電子顯微鏡(Scanning Electron Microscopy,SEM) 24
2-2.3磁性量測 26
第三章 實驗結果與討論 30
3-1結構分析 30
3-2磁性分析 36
3-2.1 ZFC(零場冷卻)與FC(場冷卻) 36
3-2.2 磁滯曲線 42
第四章 總結 47
第五章 參考文獻 49
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