I. Introduction 1 I.1 Fundamental Energy Contributions in Ferromagnetic Systems 1 I.1.1 Exchange Interaction and Exchange Energy Density 1 I.1.2 Magnetocrystalline Anisotropy and Effective Anisotropy 2 I.1.3 Magnetostatic Energy and Demagnetization Effects 3 I.1.4 Zeeman Energy: Interaction with External Magnetic Fields 4 I.2.Magnetic Domain Walls: Structure and Characteristics 4 I.3 Factors Determining DW Configuration and DMI Stabilization 5 I.4 The Dzyaloshinskii-Moriya Interaction (DMI) and Chiral Magnetism 6 I.5 Field-Driven Dynamics: Creep Regime (Thermal activation) 7 I.5.1. Field-Driven Dynamics: Flow Regime (Steady State and Walker Breakdown) 8 I.6 Spin-Transfer Torque (STT) based Application 9 I.7 Limitations of STT Architectures 10 I.8 Spin-Orbit Torque Theory and Generation Mechanisms 10 I.8.1 SOT Geometry and Structure 10 I.8.2 SOT Generation Mechanisms 11 I.8.3 Components of SOT: Damping-Like (DL) and Field-Like Torques(FL) 12 I.8.4 Analysis method for DL and FL 12 I.8.5 Advantages of SOT over STT for Memory Applications 15 I.9 Spin Torque Majority Gate (STMG) Logic 15 II. Device Fabrication 17 II.1 DC magnetron sputtering 17 II.2 Photolithography 19 II.3 Ion Beam Milling 20 III. Validation of the Majority Function Operation 22 III.1 DMI Chirality-Based Field-Free Spin-Orbit Torque (FF-SOT) Magnetization switching 22 III.2 Establishing Majority Operation Mode 26 III.2.1 AND Gate Implementation (Input I1 = 0 Fixed) 27 III.2.2 OR Gate Implementation (Input I1 = 1 Fixed) 27 III.3 Fabricating MOSFET device and STMG device with check the MOSFET compatibility 30 IV. Asymmetric DW Motion in Trapezoidal-shape Wire 37 IV.1 Schematics of trapezoidal wire configuration and basic DW measurement 39 IV.2 SOT-driven DW motion trend in trapezoidal wire 41 IV.3 Direct comparison between SOT-driven DW motion according to the flow direction in trapezoidal wire and control sample 44 IV.4 Analytic expression of SOT-driven DW motion according to DW energy 46 V. Enhancement of Spin-Orbit Torque Efficiency by Extended Width Heavy Metal Layer 53 V.1 Sample structures for various wire configurations 54 V.2 AHE measurement in various etched cases 56 V.3 Sample fabrication method 59 V.4 Measurements of SOT efficiency and DW mobility (DW) 60 V.5 SOT efficiencies ES (2–20, 30) and CS(2–20, 2–20) series samples 62 V.6 Precise calculation of JC using resistivity of ES (2–20, 30) series samples 63 V.7 SOT efficiencies ES (3, 3–20) series samples 65 V.8 Generalized Sucksmith-Thompson measurement for identification of magnetic state of various sample geometries 66 V.9 Image process method for designating the precise DW position 68 V.10 DW measurement in CS, ES series using SOT-driven DW motion 70 V.11 Correlation between DL-SOT efficiency and DW 71 V.12 DW pinning field evaluation 73 V.13 FM wire position dependent 74 V.14 Universal behavior of SOT efficiencies 76 VI. Summary 78 References 80
