臺灣博碩士論文加值系統

總共九個TMR多層膜包含Co(500 )/Fe(50 )/MgO(X)/Fe(500 ) (X=8、16、25)用分子束磊晶成長在MgO(001)、(011) and (111)上。使用磁阻曲線及磁滯曲線量測得到幾項重要的結果：(1)磁阻率不高，均在0.2%以下。(2)絕緣層的厚度影響不明顯，但以成長於(111)面上，MgO=25之樣品具備最高之磁阻值。(3)有強烈的平面異向性。(4)可能也是本實驗之最重要結果，即在許多特定磁場方向下MR值呈現明顯的負值。
負磁阻的產生，可能與Co的極化率（Polarization）有關，磁阻率隨著角度變化而改變，代表樣品在不同角度下其電子能量密度 （Density Of State）分佈的不同，即其費米表面分佈不對稱，造成不同角度量測時有不同的極化率（Polarization）的結果。
平面異向性隨著MgO晶格面之改變而不同，但基本上呈現180∘或90∘的對稱，亦即MR隨磁場方向改變而變化，除了 Co(500 )/Fe(50 )/MgO(8)/Fe(500 )/MgO(001)這基板外，其它MR呈現cos(2θ)之週期變化，而上述例外之樣品，則呈現cos(4θ)之週期。

Experiments have been performed by using series of crystalline Co(500 )/Fe(50 )/MgO(X)/Fe(500 ) films (where X=8、16、25).The samples have prepared by molecular beam epitaxy on MgO(001,011,111) substrates. The hysteresis and magnetoresistance measurements have performed and have found the some meaningful result.They are (1)MR ratios are not found very high and the average values are smaller than 0.2%. (2)The thickness of insulating MgO layer makes a little factor of MR ratio and it shows higher for the sample which has thickness of insulating layer is 25, grown on MgO (111). (3) Intensive anisotropic (4) Inverse tunnel magnetoresistance under some direction of magnetic field indicates some important significant in the present experiment.
Inverse tunnel magnetoresistance maybe have relation with polarization of Co. Different MR ratio due to changing of direction of magnetic field means that each place of the surface of sample has different density of state. So Fermi sphere is unsymmetrical and shows the different polarization due to applying magnetic field at different angle.
The anisotropic has relation with MgO lattice planes and it has 180∘or 90∘symmetry. The experimental values of MR ratio due to circumrotation of magnetic field, match with cos2θperiod, where as the MR ratio fit with cos4θ period for the sample Co(500 )/Fe(50 )/MgO(8)/Fe(500 )/MgO(001) .

第一章? 序論 ………..……………………………………………….1
1-1 前言 …….……………………………………………...1
1-2 磁阻簡介 …………………………………………………3
1-2-1 常磁電阻 (Ordinary magnetoresistance)…………………..3
1-2-2 異向磁電阻 (Anisotropy magnetoresistance) ……………4
1-2-3 巨磁電阻 (Giantmagnetoresistance) .……………………5
1-2-4 龐磁電阻 (Colossal magnetoresistance) ………………5
1-2-5 穿遂磁電阻(Tunneling magnetoresistance) ………………6
第二章 理論基礎 …… ………………………………………………8
2-1 磁性的起源 …………………………………………………8
2-2 Julliere’s Model …………………………………………8
2-3 穿遂磁阻 ………………………………………………12
第三章 實驗儀器與實驗方法 ……………………………………15
3-1 實驗儀器 …………………………………………………15
3-1-1 長膜系統 ………………………………………………15
3-1-2 磁性測量-振動樣品測磁儀（VSM） ………………………23
3-1-3 電性測量系統 ………………………………………………26
3-2 實驗步驟 ………………………………………………27
3-2-1 實驗流程圖 ………………………………………………27
3-2-2 長膜前的準備 ……………………………………………27
3-2-3 開始長膜 …………………………………………………28
3-2-4 磁性測量 …………………………………………………29
3-2-5 電性測量 …………………………………………………29
第四章 實驗結果與討論 …………………………………………30
4-1 實驗數據 …………………………………………………30
4-1-1 Co/Fe/MgO(8)/Fe/MgO(001) 測量結果 …………………31
4-1-2 Co/Fe/MgO(8)/Fe/MgO(011)、(111)的量測結果 …………32
4-1-3 Co/Fe/MgO(16)/Fe/MgO(001)、(011)、(111)之量測結 ..41
4-1-4 Co/Fe/MgO(25)/Fe/MgO(001)、(011)、(111)之量測結 ..47
4-2 實驗結果討論 ……………………………………………54
第五章 結論 ……………………………………………………57
REGERENCES ……………………………………………………59

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