鈀鈷薄膜中異常霍爾效應符號翻轉行為與其介面 之磁特性研究

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賴誼峰(Yi-Feng Lai) 查詢紙本館藏

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物理學系

論文名稱

鈀鈷薄膜中異常霍爾效應符號翻轉行為與其介面之磁特性研究
(The Sign Reversal of Anomalous Hall Effect and the Interfacial Magnetic Properties in PdCo Thin Films)

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★ 具電阻切換行為之氧化鋁磁性穿隧接面中低頻雜訊與傳輸機制研究

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至系統瀏覽論文 (2026-6-30以後開放)

摘要(中)

在磁性薄膜中異常霍爾效應的符號翻轉行為已經被廣泛研究。然而，在重金屬加上鐵磁材料的磁性薄膜系統中，重金屬與鐵磁層的之間介面在討論磁性薄膜的磁性及傳輸行為中扮演很重要的角色。在本論文研究中利用基於第一原理計算開發的JunPy方法來計算鈀鈷雙層膜的自旋軌道矩，結果顯示在鈀鈷雙層膜中來自鈀鈷介面以及來自鈀或鈷表面的磁異向性貢獻之間有一個水平異向性及垂直異向性互相競爭的關係。接續透過分析鈀鈷雙層膜不同原子層之間的自旋軌道矩，可以分辨出磁異向能的貢獻主要來自薄膜的介面還是表面。此外，我們也測量了不同厚度下鈀鈷薄膜的異常霍爾效應，並觀察到當鈷的厚度為1.4奈米時，異常霍爾電阻會發生符號翻轉的現象。這主要是由於不同異常霍爾效應機制之間的競爭所導致的結果，例如貝里曲率的變化和雜質散射。相反的，我們並沒有在改變鈀的厚度時，發現異常霍爾電阻符號翻轉的行為。異常霍爾電阻隨著鈀的厚度增加時，主要是被電流的分流效應所影響，進而使異常霍爾電阻隨著鈀厚度增加而減小，並且當鈀的厚度接近其平均自由徑時變化趨於平緩。我們的結果不僅加深了我們對鈀鈷薄膜在不同厚度下的磁性與電性行為變化的理解，也提供了一個新的計算方式來研究在重金屬和鐵磁材料的薄膜中介面或其表面對磁異向性的影響。

摘要(英)

The sign reversal of the anomalous Hall resistance in magnetic thin films has been extensively researched. However, in systems that combine heavy metals (HM) and ferromagnetic (FM) materials, the interface plays a crucial role in influencing the magnetic and transport properties of HM/FM thin films. In our study, we utilized our JunPy package, which is based on density functional theory (DFT) calculations, to calculate the spin-orbit torque (SOT) in Pd/Co bilayers. The results indicate a competition between in-plane magnetic anisotropy and perpendicular anisotropy coming from the Pd/Co interface or the Pd and Co surfaces. The layer-resolved SOTs offer a method to distinguish the magnetic anisotropy energy contributions from the interface or surfaces in Pd/Co bilayers. Furthermore, we measured the relationship between thickness and the anomalous Hall effect (AHE) in Pd/Co thin films. A change in the AHE sign occurs at approximately 1.4 nm Co thickness in Pd/Co thin films with different Co thicknesses. This observation is consistent with the competing mechanisms of the AHE, such as intrinsic Berry curvature and impurity scattering. In contrast, there is no sign change when altering the thickness of Pd in Pd/Co thin films. The anomalous Hall resistance decreases as the Pd thickness increases due to the shunting effect. Eventually, the anomalous Hall resistance levels off after increasing the Pd thickness to a critical value comparable to its mean free path. These results deepen our understanding of both the magnetic and transport behaviors of Pd/Co thin films with different thicknesses and provide a novel perspective for studying magnetic anisotropy at the interface in HM/FM systems.

關鍵字(中)

★ 異常霍爾效應
★ 第一原理
★ 磁異向性
★ 自旋矩
★ 磁性薄膜

關鍵字(英)

★ anomalous Hall efect
★ first-priciples
★ magnetic anisotropy
★ spin torque
★ magnetic thin film

論文目次

中文摘要.......................................................................................................... i
Abstract............................................................................................................ ii
Contents ........................................................................................................... iii
List of Figures.................................................................................................. v
Chapter 1. Introduction ................................................................................. 1
Chapter 2. Magnetism and Magnetic Anisotropy ......................................... 8
2.1 Magnetism . . . . . . . . . . . . . . . . . . . . . . . . . . 8
2.2 Magnetocrystalline Anisotropy . . . . . . . . . . . . . . . 10
2.2.1 Cubic Anisotropy . . . . . . . . . . . . . . . . . . . . . . 11
2.2.2 Uniaxial Anisotropy . . . . . . . . . . . . . . . . . . . . . 11
2.3 Shape Anisotropy . . . . . . . . . . . . . . . . . . . . . . 12
2.4 Magnetic Anisotropy Energy . . . . . . . . . . . . . . . . 13
Chapter 3. Hall effect....................................................................................15
3.1 Ordinary Hall effect . . . . . . . . . . . . . . . . . . . . . 15
3.2 Anomalous Hall effect . . . . . . . . . . . . . . . . . . . 17
3.2.1 Intrinsic Mechanism . . . . . . . . . . . . . . . . . . . . . 18
3.2.2 Extrinsic Mechanisms . . . . . . . . . . . . . . . . . . . . 18
Chapter 4. Experimental Methods ................................................................19
4.1 Magnetron Sputtering . . . . . . . . . . . . . . . . . . . . 19
4.2 Sample Fabrication . . . . . . . . . . . . . . . . . . . . . 20
4.3 Hall measurement . . . . . . . . . . . . . . . . . . . . . . 21
Chapter 5. Computational Details.................................................................23
5.1 Structure Geometry . . . . . . . . . . . . . . . . . . . . . 23
5.2 Structural Relaxation . . . . . . . . . . . . . . . . . . . . 24
5.3 Electrical and Spin Moment Calculation . . . . . . . . . . 25
5.4 Parameters for Spin Torque Calculation . . . . . . . . . . 25
Chapter 6. Results and Discussion................................................................27
6.1 DFT-based Spin Torque Calculation of Co Thin Film . . . 27
6.1.1 Spin Torque and Magnetic Anisotropy Energy . . . . . . . 27
6.1.2 Layer-resolved Spin Torque . . . . . . . . . . . . . . . . . 29
6.2 DFT-based Spin Torque Calculation of Pd/Co Bilayers . . 30
iii
6.2.1 Thickness Dependence of Spin Torque and Magnetic Anisotropy
Energy . . . . . . . . . . . . . . . . . . . . . . . . . . . . 30
6.2.2 Thickness Dependence of Effective Anisotropy Energy . . 32
6.3 Co Thickness Dependence of Electrical Measurement . . . 35
6.3.1 The measurement for Pd(5 nm)/Co(1.4 nm)/Pd(3 nm) . . . 35
6.3.2 Thickness Dependence of Anomalous Hall Resistance . . . 36
6.4 Pd Thickness Dependence of Electrical Measurement . . . 36
6.4.1 Thickness Dependence of Resistance . . . . . . . . . . . . 37
6.4.2 Thickness Dependence of Anomalous Hall Resistance . . . 37
Chapter 7. Conclusion...................................................................................42
References........................................................................................................44
Appendix..........................................................................................................48
A.1 The LabVIEW Program for Hall Measurement . . . . . . . 48
A.2 The Parallel Circuit Model in AHE . . . . . . . . . . . . . 49

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指導教授

唐毓慧洪振湧(Yu-Hui Tang Jhen-Yong Hong)

審核日期

2024-7-26

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