臺灣博碩士論文加值系統

我們以自製的磁光柯爾效應儀(SMOKE)來進行超薄膜的表面磁性研究，由本實驗室先前研究可知，Co / Ag / Pt (111)系統歷經升溫過程時鈷、銀原子間有交換的現象，最後銀原子會完全翻至樣品表面，待交換完成後鈷會與白金形成合金。為了瞭解在此過程中磁性的變化，我們分別作了1ML Co在1ML Ag與2ML Ag上的磁性探測與2ML Co和4ML Co在1ML Ag上的磁性探測。
在1ML Co / x ML Ag / Pt (111)系統中( x = 1、2 )，磁化易軸方向為垂直樣品表面方向，隨著溫度的升高使鈷、銀原子開始交換後，柯爾訊號強度與矯頑力Hc都會有增大的行為；交換完成後，柯爾訊號因為鈷與白金形成合金而繼續增大，但Hc卻下降了；故可知鈷銀原子之間混雜時應發生一些電子結構方面的變化，影響了磁性。在此兩系統中，因為鈷的厚度不變，所以在740K退火效應後，柯爾訊號的強度的增強大致相同，而Hc則會因為銀厚度的增加，而有明顯的增大。
在x ML Co / 1ML Ag / Pt (111)系統中( x = 2、4 )，因鈷銀間lattice mismatch的原因，磁化易軸方向為平行樣品表面方向，隨著升溫效應使鈷、銀原子交換混雜，只要鈷、銀原子間電子交互作用力夠強且外界提供的熱能足夠，便能使易軸由平行樣品表面轉為垂直樣品表面，即發生了spin reorientation transition(SRT)現象，且在發生SRT現象以後，柯爾訊號強度與Hc都有明顯增強的趨勢。但因為鈷厚度的增加，銀的影響相較之下較不明顯了。
在所有系統中，經過升溫退火效應以後，皆無法回到原來的趨勢，可知鈷、銀原子交換現象與鈷、白金合金的形成皆是不可逆的，我們也發現了在合金形成後的樣品其Hc有一特殊的趨勢，隨著溫度有一類似階梯(step)的下降。
由以上磁性的測量發現，銀與鈷原子之間發生的一些電子變化有助於增強柯爾訊號與矯頑力，而且使磁性物質的易軸方向較喜歡以垂直樣品表面的方式排列(PMA)，對於製作磁光記憶材料有很大的幫助，因此其物理現象的相關探討，是我們要努力的方向。

Chapter 1 緒論...............................................1
Chapter 2 基本原理...........................................3
2-1 薄膜成長..................................................3
2-1-1 成長模式................................................4
2-1-2 影響薄膜成長的因素......................................4
2-2 磁性物質..................................................5
2-2-1 磁性物質的種類..........................................5
2-2-2 鐵磁性物質..............................................7
2-2-3 居禮溫度................................................9
2-3 磁異向性..................................................9
2-3-1 磁異向能（anisotropic energy）.........................10
2-3-2 影響磁異向性的因素.....................................11
Chapter 3 實驗原理與儀器....................................14
3-1 超高真空系統（UHV）......................................14
3-1-1 需要超高真空的理由.....................................14
3-1-2 超高真空腔與抽器系統...................................16
3-1-3 樣品清潔與升降溫系統...................................17
3-1-4 蒸鍍系統...............................................19
3-1-5 壓力量測系統 ... .......................................20
3-2 歐傑電子能譜術（Auger Electron Spectroscopy）............20
3-2-1 歐傑效應...............................................20
3-2-2 歐傑電子能譜 ...........................................21
3-2-3 阻滯電場分析儀.........................................23
3-2-4 歐傑能譜術的應用.......................................25
3-3 低能量電子繞射儀.........................................27
3-3-1 LEED基本原理...........................................27
3-3-2 RFA-LEED工作原理.......................................28
3-4 表面柯爾磁光效應.........................................29
3-4-1 MOKE理論...............................................29
3-4-2 SMOKE測量原理..........................................31
3-4-3 SMOKE儀器裝置..........................................33
Chapter 4 實驗結果與討論....................................35
4-1 實驗前的準備.............................................35
4-1-1 銀鍍源的刻度 ...........................................35
4-1-2 鈷鍍源的刻度 ...........................................36
4-2 1ML Co / 1ML Ag / Pt (111)超薄膜的磁性探討...............36
4-2-1 成長模式...............................................36
4-2-2相同退火溫度之磁滯曲線變化對時間的關係..................41
4-2-3 磁性探討...............................................44
4-3 1ML Co / 2ML Ag / Pt (111)超薄膜的磁性探討...............55
4-3-1 成長模式...............................................55
4-3-2 磁性探討...............................................55
4-4 2ML Co / 1ML Ag / Pt (111)超薄膜的磁性探測...............64
4-4-1 成長模式...............................................64
4-4-2 磁性探討...............................................66
4-5 4ML Co / 1ML Ag / Pt (111)超薄膜的磁性探討...............74
4-5-1 成長模式...............................................74
4-5-2 磁性探討...............................................76
Chapter 5 結論...............................................84
參考資料.....................................................87

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