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研究生: 曾筱嵐
論文名稱: Co / Ag / Pt (111)原子交換與表面磁性的研究
指導教授: 沈青嵩
學位類別: 碩士
Master
系所名稱: 物理學系
Department of Physics
論文出版年: 2002
畢業學年度: 90
語文別: 中文
論文頁數: 91
中文關鍵詞: 柯爾磁光效應自旋翻轉矯頑磁場垂直磁異向性歐傑電子效應儀低能量電子效應儀
英文關鍵詞: SMOKE, spin reorientation transition, coercive field, PMA, AES, LEED
論文種類: 學術論文
相關次數: 點閱:251下載:8
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  • 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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