臺灣博碩士論文加值系統

在凝聚態物質研究領域中，通過自旋-軌道耦合(spin-orbit coupling)引起熱量、自旋和電荷明顯的相互轉換的材料引起了相當大的關注。特別感興趣的是為自旋電子學應用生成、檢測和操作自旋極化(spin polarized current)或純自旋電流(pure spin current)現象。通過操縱電子的自旋自由度，可以設計具有增強功能的自旋電子學器件。
已經研究了許多材料用於產生自旋電流，例如半導體、過渡金屬、拓撲半金屬等。對於過渡金屬而言，自旋霍爾角度(θ_SH, spin Hall angle)的數值由能帶結構決定，並且是特定金屬固有的。通常，過渡重金屬如鎢(W)和鉑(Pt)由於強自旋-軌道耦合而具有較大的電荷到自旋轉換。
在先前的研究中，探索了鎳銅(NiCu)合金與釔鐵石榴石(Y3Fe5O12,YIG)雙層結構中的自旋賽貝克效應(spin Seebeck effect)，發現在NixCu1-x合金中存在顯著自旋電荷轉換的增強現象，其歸因於自旋漲落(spin fluctuation)。值得注意的是，Ni80Cu20合金在順磁(paramagnetic)態下表現出極大的自旋霍爾角度，約為θ_SH=46%，比鉑高出4.5倍，且其居裡溫度(Curie temperature)約為300 K。通過減小薄膜厚度，由於有限尺寸效應(finite size effect)，Ni80Cu20薄膜從鐵磁(ferromagnetic)態過渡到順磁態。
在先前研究的基礎上，我們進一步研究了Ni80Cu20合金在鐵磁態內熱、自旋和電荷的相互轉換。本研究特別探索了自旋霍爾磁阻(spin Hall magnetoresistance)和自旋能斯特熱電(spin Nernst induced thermal power)現象。此外，還對在YIG基板上得到Pt與Ni80Cu20合金的結果進行了比較分析，以探討不同材料的熱自旋轉換效率與影響。

Materials that exhibit a pronounced inter-conversion of heat, spin, and charge through spin-orbit coupling have garnered considerable attention in the field of condensed matter research. Of particular interest is the generation, detection, and manipulation of spin polarized or pure spin current phenomenon for spintronics applications. By manipulating the spin degree of freedom of electrons, spintronic devices can be designed with enhanced functionality.
Many materials have been explored to generate spin current, such as semiconductors, transition metals, topological semimetals, and more. For the transition metals, the values of spin Hall angles (θ_SH ) are dictated by the band structures and inherent to the specific metals. Usually, transition heavy metal such as W and Pt is known to have large charge to spin conversion due to strong spin-orbit coupling (SOC).
In previous study, the spin Seebeck effect in a NixCu1-x/YIG structure is explored, leading to the discovery of a significant enhancement in spin-to-charge conversion within the NixCu1-x alloy, attributed to spin fluctuations. Notably, the Ni80Cu20 alloy, characterized by a Curie temperature of approximately 300 K, exhibits an extraordinary large spin Hall angle of around θ_SH=46% in the paramagnetic state, surpassing Pt by 4.5 times. Through the reduction of film thickness, the Ni80Cu20 film undergoes a transition from the ferromagnetic (FM) state to the paramagnetic (PM) state due to the finite size effect.
Building upon the previous findings, we study further the inter-conversion of heat, spin, and charge within the Ni80Cu20 alloy in the FM state. This investigation specifically explores the spin Hall magnetoresistance (SMR) and spin Nernst induced thermal power (SNITP). Moreover, a comparative analysis is conducted between the results obtained from Pt and Ni80Cu20 alloys on YIG substrates to explore the thermal spin conversion efficiency and influence on different materials.

Abstract iii
1 Introduction 1
2 Background 9
2.1 Basic Concepts 9
2.1.1 Spin Current Generation 9
2.1.2 Spin Current Detection 13
2.2 The Ni80Cu20 alloy 16
2.3 Spin Transport Theory Driven by JC and T 18
2.3.1 Theory of Spin Hall Magnetoresistance 18
2.3.2 Theory of Spin Nernst Induced Thermal Power (SNITP) 23
2.4 Phenomena in Magnetic Material 26
2.4.1 Magnetism 27
2.4.2 Anisotropic Magnetoresistance (AMR) 36
2.4.3 Anomalous Hall Effect (AHE) 37
2.4.4 Magnetization-Dependent Thermal Voltage 40
2.4.5 Anomalous Nernst Effect (ANE) 41
3 Method 43
3.1 Sample Preparation 44
3.1.1 Substrate Cleaning 44
3.1.2 Photo-lithography 45
3.1.3 Magnetron Sputtering Deposition 48
3.1.4 X-ray Reflection (XRR) 50
3.2 Physical Properties Measurement 51
3.2.1 X-ray Diffraction (XRD) 51
3.2.2 Vibrating Sample Magnetmeter (VSM) 52
3.2.3 Electrical Four-point Probe Measurement 54
3.2.4 Thermoelectric Measurement 56
4 Result and Discussion 59
4.1 Introduction 59
4.2 Spin Hall Magnetoresistance 60
4.2.1 Ni/Si 61
4.2.2 Pt/YIG 63
4.2.3 NiCu/YIG 65
4.3 Spin Seebeck Effect Measurement 67
4.3.1 NiCu/YIG 68
4.4 Spin Nernst Effect Measurement 70
4.4.1 Experiment Setup 70
4.4.2 Pt/YIG 72
4.4.3 NiCu/YIG 76
5 Summary 79
References 81

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