Preface xi

1 Introduction to Spintronics and Diluted Magnetic Semiconductors (DMSs) 1
Danish Arif, Adeel Younas Abid, Kashif Safeen, Adnan Ali, Ghafar Ali, and Akif Safeen

1.1 Fundamentals of Spintronics 1
1.1.1 Spin Quantum Number, Polarization, and Magnetic Moment 1
1.1.2 Spin-Dependent Transport Phenomena 3
1.1.3 Spin-Based Devices 6
1.1.4 Comparison with Conventional Electronics 7
1.1.5 Overview of Diluted Magnetic Semiconductors (DMSs) 8
1.1.6 Applications of DMSs 13
1.1.7 Historical Development and Current Trends 14
1.1.8 Controversies on Room-Temperature Ferromagnetism 17
1.1.9 Current Research Directions 18
1.1.10 2D DMSs: MoS 2, Graphene, and Other Transition Metal Dichalcogenides 19
1.1.11 Hybrid DMS Nanostructures for Spintronics 20
1.1.12 Importance of Nanostructuring in Spintronics 21
1.1.13 Advantages of Nanostructured Spintronic Materials 26
1.1.14 Future Prospects 27

2 Material Design and Synthesis of Nano-Structured DMS 37
Nasar Ahmed and Irsa Ghazal

2.1 Overview of Diluted Magnetic Semiconductor Materials 37
2.2 Synthesis Techniques 38
2.2.1 Hydrothermal Method 38
2.2.2 Precipitation Method 40
2.2.3 Sol–Gel Method 42
2.2.4 Molecular Beam Epitaxy 44
2.2.5 Chemical Vapor Deposition 44
2.2.6 Pulsed Laser Deposition 47
2.3 Nanostructuring Approaches 48
2.3.1 Quantum Dots 48
2.3.2 Nanowires 49
2.3.3 Thin Films 49
2.3.4 Multilayered 50
2.4 Selection of Host Semiconductors and Magnetic Dopants 50
2.5 Challenges in Controlled Doping and Defect Engineering 53

3 Structural and Magnetic Characterization Techniques 59
Muhammad Sheeraz, Asif Ullah, and Azizur Rahman

3.1 Importance of Structural Analysis in Magnetic Semiconductors 59
3.2 XRD of Bulk and Polycrystalline Magnetic Semiconductors 60
3.2.1 Fundamentals of Powder Diffraction 60
3.2.2 Transition from Bulk to Thin Films: Limitations and Importance of Advanced XRD Techniques 63
3.3 XRD of Thin Films and Single-Crystalline Magnetic Semiconductors 64
3.3.1 Symmetric Θ–2Θ Scan 64
3.3.2 Rocking Curves 66
3.3.3 Azimuthal Phi (φ) Scans 66
3.3.4 Reciprocal Space Mapping (RSM) 67
3.4 Electron Microscopy in Magnetic Semiconductors 68
3.4.1 Scanning Electron Microscopy (SEM) 68
3.4.2 Transmission Electron Microscopy (TEM) 70
3.5 Superconducting Quantum Interference Device (SQUID) Magnetometry and Vibrating Sample Magnetometry
(VSM) 73
3.5.1 Introduction to Magnetic Characterization 73
3.5.2 SQUID Magnetometry 74
3.5.3 Applications of SQUID in Spintronics 76
3.5.4 Advantages and Limitations of SQUID Magnetometry 77
3.6 Vibrating Sample Magnetometry (VSM) 78
3.6.1 Principle of VSM 78
3.6.2 Applications of VSM in Spintronics 79
3.6.3 Advantages and Limitations of VSM 80
3.7 Spectroscopic Techniques 81
3.7.1 X-ray Magnetic Circular Dichroism (XMCD) 81
3.7.2 X-ray Photoelectron Spectroscopy (XPS) in Magnetic Semiconductors 84

4 Nano-Engineered Magnetic Semiconductors for Spintronics 91
Sana Ishfaq, Sara Yaseen, Abdul Ghafar Wattoo, Kamran Ikram, Muhammad Farhan Jahangir Chughtai, and Muhammad Ashraf

4.1 Introduction 91
4.2 Fundamentals of Magnetic Semiconductors 92
4.2.1 Intrinsic Magnetic Semiconductors 93
4.2.2 Dilute Magnetic Semiconductors (DMS) 93
4.3 Nanostructuring Approaches 94
4.3.1 Major Nanostructuring Approaches 94
4.4 Exchange Interaction Mechanisms 97
4.4.1 RKKY Interaction 97
4.4.2 Double Exchange 97
4.4.3 Super Exchange 98
4.4.4 Magnetic Ordering 98
4.5 Role of Nanostructuring in Magnetic Semiconductors 98
4.5.1 Quantum Confinement Effects 98
4.5.2 Surface and Interface Effects 99
4.5.3 Strain Engineering 100
4.5.4 Spin Transport Enhancement 100
4.5.5 Magnetic Anisotropy Control 100
4.5.6 Defect and Dopant Distribution Control 101
4.5.7 Reduced Dimensional Systems 101
4.5.8 Enhancement of Curie Temperature 101
4.5.9 Integration with Emerging Materials 101
4.6 Mechanism of Ferromagnetism in Magnetic Semiconductors 101
4.6.1 Origin of Magnetic Moments 101
4.6.2 Quantum Mechanical Exchange Interaction 102
4.6.3 Carrier-Mediated Exchange (RKKY Mechanism) 102
4.6.4 Double Exchange Mechanism 102
4.6.5 Super Exchange Interaction 102
4.7 Spin Transport Phenomena 103
4.7.1 Spin-Polarized Current 103
4.7.2 Spin Injection 103
4.7.3 Spin Diffusion 104
4.7.4 Spin Drift 104Contents ix
4.7.5 Spin Relaxation Mechanisms 105
4.7.6 Spin Precession 105
4.7.7 Spin-Transfer Torque (STT) 105
4.7.8 Magnetoresistance Effects 106
4.8 Applications of Magnetic Semiconductors in Spintronics 106
4.8.1 Spin Field Effect Transistor (Spin-FET) 106
4.8.2 Magnetic Random-Access Memory (MRAM) 106
4.8.3 Spin-LEDs 106
4.8.4 Spin Logic Devices 106

5 Device Applications of Nanostructured DMS in Spintronics 111
Rajwali Khan and Aurangzeb Khan

5.1 Spin Field-Effect Transistors (Spin-FETs) 111
5.2 Spin-LEDs and Spin-Lasers 113
5.3 Magnetic Tunnel Junctions (MTJs) and Spin Valves 117
5.4 Emerging Devices: Spin Qubits and Spin-Orbitronics 119
5.4.1 Spin Qubits in Semiconductor Nanostructures 119
5.4.2 Spin-Orbitronics 121

6 Theoretical Modeling and Simulation of Nano-Diluted Magnetic Semiconductors 125
Mudasser Husain, Nasir Rahman, and Amir Ullah

6.1 Density Functional Theory for Magnetic Semiconductors 125
6.1.1 Introduction 125
6.2 Monte Carlo and Micromagnetic Simulations 126
6.2.1 Introduction 126
6.3 Monte Carlo Method 127
6.3.1 Generalities 127
6.3.2 Metropolis Algorithm 128
6.3.3 Thermalization Process 130
6.3.4 Size of Model and Periodic Boundary Conditions 131
6.3.5 Random Number Generators 132
6.3.6 Magnetic Models 133
6.3.7 Structure of a Monte Carlo Program 135
6.4 Regular Infinite Networks 135
6.5 Alternating Chains 140
6.6 Finite Systems 143
6.7 Exact Laws Versus MC Simulations 146
6.7.1 A Method to Obtain an ECS Law for a Regular 1D System: Fisher's Law 146
6.7.2 Small Molecules 148
6.7.3 Extended Systems 149x Contents
6.8 Some Complex Examples 154
6.9 Conclusions and Future Prospects 156
6.10 Modeling Spin Transport and Spin Relaxation 157
6.10.1 Drift–Diffusion Approach 158
6.10.2 Kinetic Transport Equations 164

7 Future Perspectives and Challenges in Nano-Engineered Magnetic Semiconductors for Spintronics 171
Rajwali Khan, Aurangzeb Khan, and Muneeb ur Rahman

7.1 Introduction 171
7.2 Scalability and Integration with CMOS Technology 171
7.3 Stability and Reliability of Nano-Engineered Magnetic Semiconductor Devices 172
7.4 Novel Materials and Heterostructures 173
7.5 Outlook on Quantum Spintronics 174
7.6 Challenges and Future Research Directions 175

References 176
Index 177