Principles of Nanomagnetism

ISBN-13: 9783319594088 / Angielski / Twarda / 2017 / 330 str.

Alberto P. Guimaraes

Opis

This is the first monograph on nanomagnetism. It emphasizes general principles and mechanisms relevant to the understanding of the intriguing properties of nanomagnetic objects including thin films, nanoparticles, nanowires, nanodisks and nanorings.

Spis treści

1 Basis of Nanomagnetism . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5

1.1 Introduction: The Importance of Nanomagnetism . . . . . . . . . . . . . . . . 5

1.2 The Origin of Nanomagnetic Behavior . . . . . . . . . . . . . . . . . . . . . . . . . 7

1.2.1 Sample Dimensions and Characteristic Lengths . . . . . . . . . . . 8

1.2.2 Broken Translation Symmetry . . . . . . . . . . . . . . . . . . . . . . . . . 9

1.2.3 Nanoscopic Samples and Magnetization Reversal . . . . . . . . . 20

1.3 Dimensionality and Critical Behavior . . . . . . . . . . . . . . . . . . . . . . . . . . 20

References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 23

2 Magnetic Domains . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 25

2.1 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 25

2.2 Interactions in Magnetic Materials . . . . . . . . . . . . . . . . . . . . . . . . . . . . 31

2.2.1 Exchange Interaction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 32

2.2.2 Magnetostatic Energy . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 34

2.2.3 Magnetic Anisotropy . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 36

2.2.4 Magnetoelastic Energy and Magnetostriction . . . . . . . . . . . . . 37

2.3 Elements of Micromagnetism . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 38

2.3.1 Equation of Motion . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 44

2.4 Magnetic Domains . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 45

2.4.1 Domain Wall Width . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 46

2.4.2 Domain Wall Motion . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 53

2.5 Random Anisotropy . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 57

References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 58

3 Magnetism of Small Particles . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 61

3.1 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 61

3.2 Particle Size and Magnetic Behavior . . . . . . . . . . . . . . . . . . . . . . . . . . . 65

3.3 Superparamagnetism . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 70

3.3.1 Superparamagnetism: The Langevin Function . . . . . . . . . . . . 78

3.4 Surface Effects . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 78

3.5 The Stoner–Wohlfarth Model . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 81

3.5.1 Inhomogeneous Magnetization Reversal . . . . . . . . . . . . . . . . . 91

3.5.2 Precessional Magnetization Reversal . . . . . . . . . . . . . . . . . . . . 94

3.5.3 Current-Induced Magnetization Reversal . . . . . . . . . . . . . . . . 97

3.6 Interaction Between Particles . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 98

References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 104

4 Magnetism of Thin Films and Multilayers . . . . . . . . . . . . . . . . . . . . . . . . 109

4.1 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 109

4.1.1 Thin Films: Planar Systems . . . . . . . . . . . . . . . . . . . . . . . . . . . . 110

4.1.2 Thin Films: Laterally Structured Systems . . . . . . . . . . . . . . . . 112

4.2 Anisotropy in Thin Films . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 115

4.3 Domain Walls and Magnetization Reversal in Thin Films . . . . . . . . . 116

4.4 Exchange Bias . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 119

4.5 Interlayer Exchange Coupling . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 124

References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 128

5 Introduction to Magnetotransport . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 131

5.1 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 131

5.2 Spin Dependent Scattering and Giant Magnetoresistance . . . . . . . . . . 138

5.2.1 Valet–Fert Model for GMR . . . . . . . . . . . . . . . . . . . . . . . . . . . . 144

5.3 Tunnel Magnetoresistance (TMR) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 145

References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 150

6 Magnetism of Nanodisks, Nanorings and Nanowires . . . . . . . . . . . . . . . 153

6.1 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 153

6.2 Nanodisks . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 153

6.3 Nanorings . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 160

6.4 Nanowires . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 163

References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 172

7 Magnetic Recording . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 177

7.1 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 177

7.2 Principles of Magnetic Recording . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 178

7.3 Novel Magnetic Recording Systems . . . . . . . . . . . . . . . . . . . . . . . . . . . 182

7.3.1 Nanodisk and Nanoring Memories . . . . . . . . . . . . . . . . . . . . . . 183

7.3.2 Domain Wall Memories . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 185

References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 187

A Units in Magnetism . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 189

B Physical Constants . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 193

Authors . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 195

Materials . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 199

Symbols . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 201

References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 204

Index . . . . . . . . . . . . . . . . . . . . . . . . . . . 

O autorze

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.

Blurb

The second edition of this book on nanomagnetism presents the basics and latest studies of low-dimensional magnetic nano-objects. It highlights the intriguing properties of nanomagnetic objects, such as thin films, nanoparticles, nanowires, nanotubes, nanodisks and nanorings as well as novel phenomena like spin currents. It also describes how nanomagnetism was an important factor in the rapid evolution of high-density magnetic recording and is developing into a decisive element of spintronics. Further, it presents a number of biomedical applications. With exercises and solutions, it serves as a graduate textbook.