在這篇論文中，我們研究了交換偏壓(Exchange bias, EB)和自旋軌道矩(Spin-orbit torque, SOT)在磁阻隨機存取記憶體(Magnetic-random access memory, MRAM)技術中的應用。本論文包括三個部分，每個部分研究交換偏壓或SOT的不同面向。在第一部分中，我們發現可以使用SOT來翻轉交換偏壓，不需要使用傳統的場退火過程。第二部分提出了使用反鐵磁材料(antiferromagnet, AFM)來實現垂直磁各向異性(Perpendicular magnetic anisotropy, PMA)材料的零場SOT翻轉。我們利用水平鐵磁層產生的外漏場或藉由插入FeMn層所產生帶有z分量的自旋電子流以去除對外部磁場的依靠。這些結果展示了AFM材料在MRAM技術中的潛在用途。第三部分則探討操縱SOT效率的新方法，藉由向Pd和Pt90Ir10等自旋霍爾效應材料施加氫氣，我們發現氫氣可以增加SOT效率，為改進SOT效率和擴展自旋電子學在MRAM技術中的應用提供了新的可能性。總體而言，本論文為使用反鐵磁材料和操控SOT方面提供更多的瞭解。

In this thesis, the application of exchange bias and spin-orbit torque (SOT) in Magnetic Random-Access Memory (MRAM) technology is explored. The thesis consists of three parts, each investigating different aspects of exchange bias or SOT. In the first part, the study discovers that the exchange bias can be switched by the spin-orbit torque, without the need of traditional field-annealing process. The second part proposes using antiferromagnetic (AFM) materials to achieve zero-field SOT switching for perpendicular magnetic anisotropy (PMA) material. The study suggests using the stray-field produced by the in-plane ferromagnetic layer or inserting a FeMn layer to produce the z-component spin current to eliminate the requirement of an external magnetic field. The results demonstrate the potential usefulness of AFM materials in MRAM technology. The third part explores new methods of manipulating SOT efficiency by applying hydrogen gas to the Pd and Pt90Ir10 spin hall effect materials. The findings show that hydrogen gas can increase SOT efficiency, indicating new possibilities for improving SOT efficiency and expanding the applications of spintronics in MRAM technology. In summary, this thesis provides valuable insights and directions for further research in the field of MRAM technology.

Table of Contents
1. Introduction 1
1.1 The introduction of MRAM 1
1.2 Motivation 3
2. Background 4
2.1 Antiferromagnetism of IrMn and FeMn 4
2.2 Exchange bias 5
2.2.1 Various exchange bi as model 7
2.3. Spin current 9
2.3.1 Spin transfer torque (STT) 9
2.3.2. Spin orbit torque 11
2.4. Interaction between spin current and AFM 21
2.4.1 Thermal switching of exchange bias (Thermally-assisted STT switching) 22
2.4.2 STT modification of exchange bias 23
2.4.3 The SOT switching of AFM itself. 24
2.4.4 Spin current transmission across AFM 24
2.5. Neuromorphic application 28
2.6. Hydrogen absorption 31
3. Experimental techniques 33
3.1 Deposition technique 33
3.2 Device fabrication 34
3.2.1Photolithography and Ion-beam etching 34
3.3 Characterization and measurement 36
3.3.1 Vibrating-sample magnetometer (VSM) 36
3.3.2 Atomic Force Microscopy (AFM) and Magnetic Force Microscopy (MFM) 37
3.3.3 Magneto-Optical Kerr Effect (MOKE) and Kerr Microscopy 38
3.3.4 Harmonic Hall measurement for spin orbit torque 40
3.3.5 AHE hysteresis loop and spin-orbit torque measurement 41
4. The switching of exchange bias by spin-orbit torque in heavy metal/ferromagnet/antiferromagnet bilayer. 43
4.1 Introduction 43
4.2 Background and motivation 43
4.3 Current-pulse-induced exchange bias switching 45
4.4 Joule heating 50
4.4.1 The Time-resolved resistance measurement 52
4.4.2 Estimate temperature change by current pulses 54
4.4.3 Joule heating in AP-mode switching (or Joule heating in a Cu-based structure) 60
4.5 Role of the IrMn layer in terms of spin Hall effect 62
4.6 Ferromagnetic layer thickness dependence 63
4.7 The dependence of EB on FM domain configurations by SOT observed by MFM 65
4.8 Mechanism for exchange bias switching 67
4.9 SOT switching in AP-mode 71
4.10 Independent manipulations of FM magnetization and exchange bias 74
4.11 Conclusion 77
5. Toward zero-field switching and analog switching/multi-level switching/neuromorphic computing 79
5.1 Background and Motivation 79
5.2 Zero-field switching by stray field 80
5.3 Zero-field switching by z-component spin current 82
5.3.1 Zero field switching for [Co/Ni]2/FeMn/Pt 84
5.3.2 Reference sample 86
5.3.3 Changing the top layer to Ta 88
5.3.4 Alter the FeMn bulk spin structure by in-situ field deposition. 89
5.3.5 Cu insertion 91
5.3.6 Possible explanation discussion 92
5.3.7 Oersted field estimation 93
5.3.8 Blocking temperature 95
5.3.9 Device temperature measurement 95
5.3.10 Inverted structure: Pt/FeMn/[Co/Ni] 97
5.3.11 z-component effective field measurement by in-plane harmonic measurement (IMA sample) 98
5.4 Multi-level switching 102
5.4.1 Room temperature multi-level switching 102
5.4.2 Low-temperature (data in previous draft and need more) 103
5.4.3 Artificial neural network (ANN) application 103
6. The effect of hydrogen on the spin orbit torque. 107
6.1 Motivation 107
6.2 Experimental Setup and Hydrogen Gas Generation 107
6.3 Effects of Hydrogen Gas on Resistance 109
6.4 Influence of Hydrogen Gas on Magnetic Properties 113
6.5 Impact of Hydrogen Gas on Spin-Orbit Torque switching 114
6.6 Average total switching current 117
6.7 Exchange bias switching 118
6.8 Influence of Hydrogen Gas on Effective Field 119
6.9 Discussion 121
6.10 Conclusion 125
7. Conclusion 127
8. Reference 129

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