1 research outputs found
The microstructural and magnetic characterization in NiFe/CoO/Co trilayers and ion-beam bombarded NiFe/Fe-oxide bilayers
本研究利用雙離子束濺鍍系統製備(1)鎳鐵/氧化鈷/鈷三層薄膜,探討不同氧化鈷厚度對交換偏壓效應之影響;(2)鎳鐵/氧化鐵雙層薄膜,探討離子束轟擊氧化鐵表面對鎳鐵/氧化鐵雙層薄膜之磁性質影響。
由X光繞射儀及電子顯微鏡分析顯示:鎳鐵/氧化鈷/鈷三層薄膜分別由面心立方之鎳鐵,鹽岩結構之氧化鈷及六方最密堆積之鈷所組成。磁性質研究結果顯示:在室溫下,鎳鐵/氧化鈷/鈷三層薄膜中氧化鈷厚度為5奈米,其磁滯曲線呈現台階形狀。經由場冷至10 K之鎳鐵/氧化鈷/鈷三層薄膜中,氧化鈷厚度為5奈米之樣品具有最大之矯頑磁力(Hc ~ 286 Oe),而氧化鈷厚度為12奈米之樣品具有最大之交換偏壓場(Hex ~ -143 Oe)。磁化量對溫度之相依性(零場冷及場冷)研究顯示:鎳鐵/氧化鈷/鈷三層薄膜均具有類似自旋玻璃之行為,其不同之阻隔溫度及不可逆溫度與氧化鈷厚度造成之鐵磁/反鐵磁耦合有關。此外,極化中子反射儀研究之初步結果(如:自旋非對稱與自旋翻轉機制)顯示:磁化翻轉機制隨著外加磁場改變而不同。
在離子束轟擊氧化鐵表面之鎳鐵/氧化鐵雙層薄膜結構分析(X光繞射儀、電子顯微鏡)結果顯示:鎳鐵/氧化鐵雙層薄膜均含有面心立方結構隻鎳鐵、剛玉型六方最密堆積結構之氧化鐵,並由電子能譜化學分析儀證實鎳鐵/氧化鐵雙層薄膜界面無擴散現象。磁性質分析結果顯示:室溫下,鎳鐵/氧化鐵雙層薄膜無明顯之交換偏壓。鎳鐵/氧化鐵雙層薄膜由室溫場冷到160 K時,經70 V轟擊後之樣品磁異向性降低,使矯頑磁力(Hc ~ 18 Oe)較未轟擊之樣品小。場冷至10 K下,未經離子束轟擊之鎳鐵/氧化鐵雙層膜具有最大之矯頑磁力約204 Oe,而經70 V轟擊之樣品具有最大之交換偏壓(Hex ~ -261 Oe)。最後,由磁化量對溫度之相依性結果顯示:經70 V轟擊後之鎳鐵/氧化鐵雙層薄膜具有最高之阻隔溫度(TB ~ 100 K),而未經離子束轟擊之樣品則具有最高之不可逆溫度(Tirr. ~ 250 K)。Exchange bias (EB) is the term used to describe the unidirectional anisotropy found in a ferromagnet (FM) exchanged-coupled to an antiferromagnet (AFM). In this research, a dual ion-beam deposition technique was used to prepare the NiFe/CoO/Co trilayers with different CoO thicknesss and NiFe/Fe-oxide bilayers for ion-beam bombardment.
Results have shown that the trilayer consisted of f.c.c. NiFe, roak-salt CoO, and h.c.p. Co structures. At room temperature, the NiFe/CoO/Co trilayers exhibited soft magnetic properties with coercivity close to those of reference single NiFe and Co layer, However, a step with enhanced Hc was observed in a NiFe/CoO(5 nm)/Co trilayer. The exchange bias coupling interaction between NiFe/CoO and CoO/Co was set in when field-cooling the trilayers below the Neel temperature of CoO down to 10 K. A largest exchange bias field (Hex ~ -143 Oe) resulting from competition between top and bottom FM/AFM interfaces was found in a NiFe/CoO(12 nm)/Co trilayer. In the ZFC/FC results, the NiFe/CoO/Co trilayers exhibited spin-glass-like behavior, while the different block temperature and irreversible temperature were caused by ferromagnetic/ antiferromagnetic coupling with different cobalt oxide thickness. Moreover, the preliminary PNR data were consistent with the hysteresis loop.
The exchange coupling effects in NiFe/Fe-oxide bilayers consisted of f.c.c. NiFe and corundum h.c.p. α-Fe2O3 structures, there were no intermixing at ferromagnetic/ antiferromagnetic surface as characterized by Electron Spectroscopy for Chemical Analysis (ESCA). Without the exchange bias at 298 K, and after 70 V Ar ion bombarded observed decrease in Hc after field cooling (FC) to 160 K is mainly attributed to a reduced effective magnetic anisotropy. The hysteresis loops were measured parallel to the film surface after being field cooled from room temperature down to 10 K at 20 kOe. The enhanced coercivity (Hc ~ 204 Oe) for not bombarded NiFe/Fe-oxide bilayer and a maximum exchange bias (Hex ~ -261 Oe) was discovered at after 70 V bombarded. The results of ZFC/FC were discovered a largest block temperature (TB ~ 110 K) with 70 V bombarded, whereas the largest irreversible temperature (Tirr.) about 250 K observed at the NiFe/Fe-oxide bilayer at sample of not bombarded.目 錄
致 謝 I
摘 要 II
Abstract III
目 錄 IV
表 索 引 VI
圖 索 引 VIII
第一章、緒論 1
1-1、前言 1
1-2、應用 2
1-2-1、磁阻式隨機記憶體(MRAM) 2
1-2-2、巨磁阻(GMR) 3
1-2-3、穿隧磁阻(TMR) 4
1-2-4、自旋閥(Spin-valve)結構元件 5
1-3、研究動機與目的 6
1-4、第一章參考文獻 9
第二章、基礎理論與文獻回顧 10
2-1、雙離子束濺鍍系統之原理及應用 10
2-1-1、Kaufman離子源 10
2-1-2、End-Hall離子源 12
2-2、磁性材料 14
2-2-1、磁性物質種類與簡介 14
2-2-2、磁異向性之介紹 19
2-2-3、磁電阻 21
2-2-4、異向性磁阻 22
2-3、交換偏壓 23
2-3-1、交換耦合機制 23
2-3-2、零場冷與場冷之磁滯曲線比較 24
2-3-3、理論模型 25
2-4、文獻回顧 30
2-4-1、反鐵磁層厚度效應 30
2-4-2、鐵磁層厚度與溫度之交換耦合效應 34
2-4-3、單層及三層膜磁電阻變化 36
2-4-4、磁化量(M)與溫度(T)之關係 37
2-4-5、離子束轟擊效應 38
2-4-6、X光繞射分析 39
2-4-7、電子能譜化學分析 40
2-4-8、極性中子反射量測 42
2-5、第二章參考文獻 46
第三章、實驗 48
3-1、實驗架構 48
3-2、材料選用 50
3-3、薄膜製備 55
3-3-1、基板前處理 55
3-3-2、鍍膜參數 55
3-4、分析儀器原理之簡介 57
3-4-1、X光繞射儀(XRD) 57
3-4-2、穿透式電子顯微鏡(TEM) 60
3-4-3、震動樣品磁力計(VSM) 64
3-4-4、超導量子干涉儀(SQUID) 66
3-4-5、磁力顯微鏡(MFM) 68
3-4-6、磁電阻量測(MR) 70
3-4-7、電子能譜化學分析儀(ESCA) 72
3-4-8、極化中子反射儀(PNR) 74
3-5、第三章參考文獻 77
第四章、結果與討論 78
4-1、改變反鐵磁層厚度之研究 78
4-1-1、X光繞射分析(XRD) 78
4-1-2、穿透式電子顯微鏡(TEM)微結構分析 80
4-1-3、震動樣品磁力計量測(VSM) 87
4-1-4、超導量子干涉儀(SQUID)磁性量測 92
4-1-5、原子力顯微鏡(AFM)及磁力顯微鏡(MFM)分析 99
4-1-6、磁電阻(MR)量測 101
4-1-7、極化中子反射儀(PNR)量測 106
4-2、離子束轟擊反鐵磁層之研究 109
4-2-1、X光繞射分析(XRD) 109
4-2-2、穿透式電子顯微鏡(TEM)微結構分析 111
4-2-3、電子能譜化學分析儀(ESCA) 114
4-2-4、震動樣品磁力計量測(VSM) 117
4-2-5、超導量子干涉儀(SQUID)磁性量測 119
4-2-6、原子力顯微鏡(AFM)及磁力顯微鏡(MFM)分析 123
4-3、第四章參考文獻 124
第五章、結論 126
i、鎳鐵/氧化鈷/鈷三層薄膜 126
ii、鎳鐵/氧化鐵雙層膜 12