Principles of Nanomagnetism (eBook)

Alberto Passos Guimarães studied physics at the University of Rio de Janeiro and obtained his Ph.D. at the University of Manchester, England. He was a visiting scientist at MIT, Cambridge, and at the Physics Institute in Uppsala, Sweden. He has worked in the field of magnetism for several years, initially studying the magnetic properties of rare-earth intermetallic compounds with Mossbauer Spectroscopy and zero-field nuclear magnetic resonance (NMR), and also studied the Magnetocaloric Effect in intermetallic compounds. In recent years he has turned his attention to nanoscale systems, such as small particles, nanowires, nanorings and nanodisks studied with different experimental techniques and micromagnetic simulation. He is the author of Magnetism and Magnetic Resonance in solids (1998) and From Lodestone to Supermagnets: Understanding Magnetic Phenomena (2005), and has also been active in the popularization of science. He is now Emeritus Researcher at the Brazilian Center for Research in Physics (CBPF) and he is a member of the Brazilian Academy of Sciences.

Foreword 7
Preface to the Second Edition 9
Preface to the First Edition 10
References 11
Contents 12
1 The Basis of Nanomagnetism 15
1.1 Introduction: The Importance of Nanomagnetism 15
1.2 The Origin of Nanomagnetic Behavior 16
1.2.1 Sample Dimensions and Characteristic Lengths 18
1.2.2 Broken Translation Symmetry 20
1.2.3 Nanomagnetic Samples and Dynamic Behavior 31
1.3 Dimensionality and Critical Behavior 31
References 36
2 Magnetic Domains 38
2.1 Introduction 38
2.2 Interactions in Magnetic Materials 45
2.2.1 Exchange Interaction 46
2.2.2 Magnetostatic Energy 49
2.2.3 Magnetic Anisotropy 51
2.2.4 Magnetoelastic Energy and Magnetostriction 53
2.3 Elements of Micromagnetism 54
2.3.1 Equation of Motion 59
2.4 Magnetic Domains 61
2.4.1 Domain Wall Width 63
2.4.2 Single-Domain Critical Diameters 69
2.4.3 Domain Wall Motion 71
2.5 Random Anisotropy 78
References 81
3 Magnetism of Small Particles 84
3.1 Introduction 84
3.2 Particle Size and Magnetic Behavior 88
3.3 Superparamagnetism 95
3.3.1 Superparamagnetism: The Langevin Function 103
3.4 Surface Effects 104
3.5 The Stoner--Wohlfarth Model 107
3.5.1 Inhomogeneous Magnetization Reversal 118
3.5.2 Precessional Magnetization Reversal 121
3.5.3 Current-Induced Magnetization Reversal 124
3.6 Interaction Between Particles 125
References 134
4 Magnetism of Thin Films and Multilayers 138
4.1 Introduction 138
4.1.1 Thin Films: Planar Systems 139
4.1.2 Thin Films: Laterally Structured Systems 143
4.2 Anisotropy in Thin Films 145
4.3 Domain Walls and Magnetization Reversal in Thin Films 148
4.4 Exchange Bias 151
4.5 Interlayer Exchange Coupling 157
References 161
5 Magnetotransport and Spin Current Effects 164
5.1 Introduction 164
5.2 Spin Dependent Scattering and Giant Magnetoresistance (GMR) 173
5.2.1 Valet--Fert Model for GMR 180
5.3 Tunnel Magnetoresistance (TMR) and Other Magnetoresistance Effects 182
5.3.1 The Anisotropic Magnetoresistance (AMR) 187
5.4 Current-Induced Domain Wall Motion and Spin Transfer Torque (STT) 189
5.5 Spin Current Effects: Spin Hall Effect, Spin Pumping, and Spin Thermal Effects 194
References 208
6 Magnetism of Nanodisks, Nanorings, Nanowires, and Nanotubes 213
6.1 Introduction 213
6.2 Nanodisks 214
6.3 Nanorings 222
6.4 Nanowires and Nanotubes 226
References 238
7 Magnetic Recording 242
7.1 Introduction 242
7.2 Principles of Magnetic Recording 243
7.3 Novel Magnetic Recording Systems 248
7.3.1 Nanodisk and Nanoring Memories 251
7.3.2 Domain Wall and Skyrmion Memories 255
References 257
Solutions to the Exercises 260
Problems of Chapter 1 260
Problems of Chapter 2 260
Problems of Chapter 3 262
Problems of Chapter 4 263
Problems of Chapter 5 264
Problems of Chapter 6 265
Problems of Chapter 7 266
Appendix A The Hall Effect 267
Appendix B Elements of Thermoelectricity 271
Appendix C Units in Magnetism 274
Appendix D Physical Constants 277
Glossary 278
Bibliography 284
Material Index 303
Symbol Index 315
Author Index 318
Subject Index 324