臺灣博碩士論文加值系統

NOL施加在自旋閥中的被固定層中有提升磁阻值的作用。在被固定層中，上下鐵磁層透過NOL鐵磁性耦合，才能維持交換場並提升磁阻。我們探討了IrMn自旋閥中，被固定層中上下鐵磁層經由不同種類NOL的耦合行為。我們使用磁控濺鍍製備下自旋閥，並使用自然氧化以及電漿氧化法製備NOL。CoFe的自然氧化NOL在被固定層中傳遞鐵磁性的耦合力，但其電漿氧化NOL則無。NiFe的自然氧化NOL顯示與CoFe類似的結果，但是其電漿氧化NOL卻造成被固定層上下鐵磁層互相夾90度耦合，使最高的磁阻值產生在與交換場夾90度之處。另外，自然氧化與電漿氧化的Fe-NOL也都顯示了此一夾90度耦合之行為。因此我們推論此一異常90度耦合現象是來自於Fe的氧化物。

Nano-oxide-layers (NOLs) inserted between the pinned layer and the antiferromagnetic (AF) layer were found to increase the magnetoresistance (MR) ratio. The ferromagnetic coupling between top and bottom pinned layers through NOLs is necessary to maintain high exchange fields and MR ratios. We have investigated the coupling between top and bottom pinned layers through various NOLs in lrMn-base spin valves. The bottom lrMn-base spin valves (Si/Ta/Cu/IrMn/bottom- CoFe/NOL/top-CoFe/Cu/CoFe/Cu/Ta) were deposited by magnetron sputtering, and NOL layers were formed by using oxygen-plasma oxidation or natural oxidation on 1 nm metallic layers. Naturally oxidized Co90Fe10 layers show a ferromagnetic coupling between top and bottom CoFe layers. The plasma-oxidized Co90Fe10 layers show non-coupling between pinned CoFe layers, plausibly due to the formation of non-ferromagnetic oxides, leading to a low MR. By using XPS analyses, we confirmed that only Fe-oxides were formed. Naturally oxidized Ni80Fe20-oxides show the same results as those of naturally oxidized Co90Fe10-oxides. In contrast, plasma-oxidized Ni80Fe20-oxides exhibit a biquadratic coupling between top and bottom pinned CoFe layers. Consequently, anomalous transfer curves were observed while measured along exchange bias direction. The highest MR was obtained when the applied field was along the direction perpendicular to the exchange bias direction. Both naturally oxidized and plasma-oxidized Fe-oxide layers exhibit similar biquadratic coupling to those of plasma-oxidized Ni80Fe20-oxides. To investigate the role of Fe in these spin valves, nano-Fe-nitrides were inserted in the pinned CoFe layers, prepared by using nitrogen plasma. MR ratio was still enhanced and ferromagnetic coupling was observed between top and bottom CoFe layers. Based on these results, we suggested that the biquadratic coupling between pinned CoFe layers results from the existence of specific Fe-oxides. The possible mechanisms for the biquadratic coupling are (1) induced biquadratic anisotropy by antiferromagnetic Fe-oxides, or (2) loose spins in ferromagnetic Fe-oxides.

第一章 簡介……………………………………………………………1
1.1 引言 ………………………………………………………………1
1.2 磁阻元件的發展 …………………………………………………1
1.3 自旋閥基本原理及其應用 ………………………………………4
1.3.1 巨磁阻效應………………………………………………………4
1.3.2 自旋閥簡介………………………………………………………5
1.3.3 自旋閥之應用……………………………………………………8
1.3.4 奈米氧化層在自旋閥中的應用…………………………………9
第二章 理論基礎與文獻回顧…………………………………………11
2.1自旋閥原理與相關背景……………………………………………11
2.1.1自旋閥磁阻來源--差異性自旋散射……………………………11
2.1.2 自旋閥的膜層結構 ……………………………………………13
2.1.2.1 種子層 ………………………………………………………14
2.1.2.2 反鐵磁層 ……………………………………………………14
2.1.2.3 鐵磁/非鐵磁/鐵磁 三層膜…………………………………16
2.1.3 影響自旋閥磁阻的主要因素 …………………………………16
2.1.3.1 鐵磁/非鐵磁/鐵磁 之選擇…………………………………16
2.1.3.2 晶體結構 ……………………………………………………16
2.1.3.3 多層膜之間的介面 …………………………………………16
2.1.3.4 多層膜的表面 ………………………………………………17
2.1.3.5 薄膜製程中的真空環境 ……………………………………18
2.1.4 其他相關之背景知識 …………………………………………19
2.1.4.1 CIP與CPP …………………………………………………19
2.1.4.2 鐵磁層間的交互耦合 ………………………………………19
2.1.4.3 Spin-filter effect ………………………………………20
2.1.4.4 鏡面反射 ……………………………………………………21
2.2 奈米氧化層及其對自旋閥的影響 ………………………………21
2.3 近年來奈米氧化層之研究課題 …………………………………22
2.3.1 NOL之材料鑑定 ………………………………………………22
2.2.2 不同物種NOL對MR的影響……………………………………23
2.2.3 NOL對鐵磁層間交互耦合力的影響……………………………23
2.2.4 NOL在自旋閥中不同位置的研究………………………………24
2.3 分析儀器原理 ……………………………………………………26
2.3.1 磁性量測－磁光科爾效應分析儀 ……………………………26
2.3.2 四點探針量測 …………………………………………………30
2.3.3 X-ray繞射儀 …………………………………………………32
2.3.4 原子力顯微鏡表面分析 ………………………………………33
第三章 實驗方法 ……………………………………………………35
3.1 實驗流程 …………………………………………………………35
3.2 樣品製備方法 ……………………………………………………35
3.2.1 基板準備 ………………………………………………………36
3.2.2濺鍍系統 ………………………………………………………36
3.2.3 濺鍍材料 ………………………………………………………38
3.2.4 NOL成長條件 …………………………………………………39
3.2.5 後退火處理 ……………………………………………………39
3.3 分析與量測方法 …………………………………………………41
3.3.1磁性量測…………………………………………………………41
3.3.2 電性量測 ………………………………………………………41
3.3.3 X光繞射…………………………………………………………41
3.3.4 表面粗糙度 ……………………………………………………41
第四章 實驗結果與討論………………………………………………42
4.1 準自旋閥系統中NOL的研究 ……………………………………42
4.1.1 PSV上表面NOL ………………………………………………42
4.1.2 PSV下表面NOL ………………………………………………46
4.2 FeMn下自旋閥中NOL位置之研究…………………………………48
4.3 IrMn/CoFe下自旋閥NOL的研究…………………………………55
4.3.1 CoFeOx in IrMn/CoFe-BSV ……………………………………55
4.3.2 Pinned layer NOL 的氧化條件………………………………57
4.3.3 CoFe/IrMn-based dual-NOL BSV熱穩定性量測………………58
4.4 BSV表層施加不同物種NOL的研究………………………………62
4.4.1 自旋閥新種子層的研究 ………………………………………62
4.4.2 BSV表層施加不同物種NOL的研究……………………………64
4.5 BSV pinned layer中的NOL的研究………………………………66
第五章 結論……………………………………………………………73
參考資料 ………………………………………………………………74

2.1 Bruce A. Gurney,Phys.Rev.Lett.71, 4023 (1993)
2.2 W. F. Egelhoff,J. Appl. Phys. 78, p273 (1995).
2.3 Y. Huai, J. Appl. Phys. 85, p5528 (1999).
2.4 Kojiro Yagami,J. Appl. Phys. 89, 6609 (2001)
2.5 S. S. Parkin, Phys. Rev. Lett.72, p3718 (1994)
2.6 William E. Bailey, Phys. Rev. B. 61, 1330 (2000)
2.7 H. Fukuzawa, J. Appl. Phys. 89, 5581 (2001)
2.8 S. S. Parkin, Phys. Rev. Lett.71, p1641 (1993)
2.9 H. J. M. Swagten , IEEE Trans. Magn. 34, p948 (1998).
2.10 W. E. Egelhoff, J. Appl. Phys. 82, p6142 (1997).
2.11 J. Zhang and G. W. Anderson, J. Appl. Phys. 85, p5528 (1999).
2.12 W. F. Egelhoff, Jr. P. J. Chen and M. D. Stile, IEEE Trans. Magn. 33, p3580 (1997).
2.13 Yiming Huai, J. Appl. Phys. 87, p5741 (2000).
2.14 H.Fukuzawa, J. Appl. Phys. 89, p5581 (2001).
2.15 H.Fukuzawa, J. Magn. Magn. Mat. 235, 208 (2001)
2.16 H. J. M. Swagten, Phys. Rev. B, 53, p9108 (1996).
2.17 Y. Kamiguchi, 1999IEEE conference, DB01.
2.18 H. Sakakima, J. Magn. Magn. Mat. L20-24, p210 (2000).
2.19 Ming Mao J. Appl. Phys. 91, p8560 (2002).
2.20 Tetsuya Mizuguchi, IEEE Trans. Magn. 37, p1742 (1997).
2.21 Kebin Li , Appl. Phys. Lett. 79, p3663 (2001).
2.22 A.Veloso, Appl. Phys. Lett. 77, p1020 (2000).
2.23 Jongill Hong, IEEE Trans. Magn. 36, p2629 (2000).
2.24 M.F.Gillies, J. Appl. Phys. 89, p6922 (2001).
2.25 J.C.S.Kools, IEEE Trans. Magn. 37, p1783 (2001).
2.26 Hideaki Fukuzawa, J. Appl. Phys. 91, p6684 (2002).
3.1 Haohua Li, J. Appl. Phys. 89, p6904 (2001).
4.1 Jongill Hong, IEEE Trans. Magn. 38, p15 (2002).
4.2 Haohua Li, J. Appl. Phys. 89, p6904 (2001).
4.3 M.F.Gillies, J. Appl. Phys. 88, p5894 (2000).
4.4 A.Veloso, Appl. Phys. Lett. 77, p1020 (2000).
4.5 Yiming Huai, J. Appl. Phys. 87, p5741 (2000).
4.6 M.F.Gillies, J. Appl. Phys. 89, p6922 (2001).
4.7 S. X. Wang, IEEE Trans. Magn. 33, p2369 (1997).
4.8 Kojiro Yagami, J. Appl. Phys. 89, 6609 (2001)
4.9 Hideaki Fukuzawa, J. Appl. Phys. 91, p6684 (2002).