Ultrathin magnetic structures IV: applications of nanomagnetism

Bretislav Heinrich, J.A.C. Bland3540219544, 9783540219545

The ability to understand and control the unique properties of interfaces has created an entirely new field of magnetism which already has a profound impact in technology and is providing the basis for a revolution in electronics. The last decade has seen dramatic progress in the development of magnetic devices for information technology but also in the basic understanding of the physics of magnetic nanostructures. Volume III describes thin film magnetic properties and methods for characterising thin film structure topics that underpin the present ‘spintronics’ revolution in which devices are based on combined magnetic materials and semiconductors. The present volume (IV) deals with the fundamentals of spintronics: magnetoelectronic materials, spin injection and detection, micromagnetics and the development of magnetic random access memory based on GMR and tunnel junction devices. Together these books provide readers with a comprehensive account of an exciting and rapidly developing field. The treatment is designed to be accessible both to newcomers and to experts already working in this field who would like to get a better understanding of this very diversified area of research.

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Table of contents :
Contents……Page 7
1 Introduction……Page 15
2.1 Background……Page 18
2.3 Developing Technology……Page 20
2.4 Future Opportunities……Page 27
References……Page 30
3.1 Introduction……Page 32
3.2 Device Concepts……Page 33
3.3 Spin Injection from Semimagnetic Semiconductors……Page 39
3.4 Spin Injection across an Air-Exposed Semiconductor Interface……Page 42
3.5 Role of Interface Structure in Spin Injection……Page 45
3.6 Ferromagnetic Metals as Spin Injecting Contacts……Page 51
3.7 Characteristics of the Fe/AlGaAs(001) Interface……Page 62
3.8 Summary……Page 66
References……Page 68
4.1.1 Concept……Page 72
4.1.2 Optical Spin Orientation in GaAs……Page 74
4.1.3 Demonstration of Optical Spin Injection and Detection……Page 77
4.1.4 Theoretical Issues in Designing Spin Electronic Devices……Page 81
4.2.1 Spin Filtering……Page 83
4.2.2 Spin Filtering Using Photoexcitation Techniques……Page 85
4.2.3 Sample Preparation……Page 87
4.3 Spin Filtering in Ferromagnet/Semiconductor Schottky Diodes……Page 88
4.3.1 Applied Magnetic Field Dependence……Page 89
4.3.2 Applied Bias Dependence……Page 91
4.3.3 GaAs Doping Density Dependence……Page 92
4.4 Spin Filtering in Ferromagnet/Barrier Layer/Semiconductor Junctions……Page 93
4.4.2 Electrical Transport Across the Ferromagnet/Semiconductor Interface……Page 94
4.4.3 Spin Dependent Transport Across the Ferromagnet/Semiconductor Interface……Page 96
4.4.4 Spin Filtering in Band Gap Engineered Ferromagnet/AlGaAs Tunnel Barrier/Semiconductor Structures……Page 97
4.5 Ballistic Spin Transport in Spin Valve Structures……Page 101
4.5.1 Sample Characterisation……Page 102
4.5.2 Optical Measurements of Spin Valve Structures……Page 103
4.6 Summary……Page 109
References……Page 110
5.1 First Spin Around the Track……Page 114
5.2.1 One Atom of Iron in Space……Page 115
5.2.2 One Iron Atom in a Non-magnetic Lattice……Page 118
5.2.3 A Unit with Two Stable States and Two Metastable States……Page 127
5.2.4 Effect of Planar Geometry on Dynamical Response……Page 138
5.3.1 Exchange Energy……Page 140
5.3.2 Magnetic Surface Charge Density……Page 141
5.3.3 A Vortex in a Circular Ultrathin Film……Page 142
5.3.4 Non-uniform states……Page 147
5.3.5 A Non-uniform System with Two-fold Plus Four-fold Anisotropy……Page 151
References……Page 161
6.1 Introduction……Page 162
6.2 The GMR Effect……Page 166
6.3 A Simple But Powerful Model……Page 167
6.4 Biasing and Device Physics……Page 171
6.5 Antiferromagnets in Spin Valves……Page 172
6.6.3 The Spin Filter (or Backed) Spin Valve……Page 174
6.6.4 Dual Spin Valve……Page 176
6.6.5 Antiparallel Pinned Spin Valves……Page 177
6.6.6 AP-free Layer Spin Valve……Page 179
6.7 Future Directions……Page 180
References……Page 187
7.1 Random Access Memories (RAMs)……Page 189
7.2 Magnetoresistive Random Access Memory (MRAM)……Page 191
7.2.1 Anisotropic Magnetoresistance-based MRAM……Page 192
7.2.2 Spin-Valve MRAM……Page 195
7.2.3 Pseudo-Spin-Valve (PSV) MRAM……Page 196
7.2.4 Magnetic Tunnel Junction (MTJ) MRAM……Page 198
7.2.5 Other MRAM Concepts……Page 200
7.3 MRAM Cell Scaling……Page 201
7.4.1 Single-domain Size and Exchange Lengths……Page 202
7.4.2 Coherent Rotation of Single-domains with Uniaxial Anisotropy……Page 203
7.4.3 Switching Astroid……Page 206
7.5.1 Single-domain-like Switching Characteristics……Page 208
7.5.2 Switching Irreproducibility……Page 211
7.5.3 Hard Axis-loops……Page 213
7.6 Micromagnetic Properties of Submicron MRAM Devices……Page 214
7.6.1 Trapped Magnetization Vortices……Page 216
7.6.2 Edge-Pinning……Page 219
7.6.3 360 °C Domain Wall……Page 220
7.6.4 Effect of Element Shape……Page 221
7.7.1 Interlayer Magnetostatic Coupling Due to End Charges……Page 222
7.7.2 Interlayer Néel Coupling Due to Interfacial Charges……Page 224
7.7.3 Inter-element Magnetostatic Interaction……Page 225
7.7.4 Switching Field Distribution……Page 226
References……Page 227
8.1 Introduction……Page 231
8.2 Magnetic Pseudo-Spin-Valve Device Switching Characteristics, Modeling, and Distributions……Page 234
8.3 The 1R0T GMRAM Architecture……Page 255
8.4 Magnetic Spin-Valve Devices for GMRAMs and GMRAM Latch Architectures……Page 258
8.5 Nonvolatile Memory Comparisons and Potential Applications……Page 260
8.6 Conclusions……Page 262
References……Page 263
D……Page 265
L……Page 266
R……Page 267
T……Page 268
Z……Page 269