Nanoscale Magnetic Materials and Applications (eBook)

Foreword 5
Preface 7
Contents 9
Contributors 21
1 Spin Dynamics: Fast Switching of Macro-spins 25
1.1 Introduction 25
1.2 Spin and Its Kinetics and Dynamics 27
1.2.1 Basic Concepts of Spin 27
1.2.2 Kinetics of Spin: Spin Current 28
1.2.3 Dynamics of Spin: Bloch Equation, Landau--Lifshitz Equation, and Landau--Lifshitz--Gilbert Equation 29
1.2.3.1 Bloch Equation 30
1.2.3.2 Landau--Lifshitz Equation and Landau--Lifshitz--Gilbert Equation 30
1.3 Macro-spin Reversal with a Static Magnetic Field 33
1.3.1 A Nonlinear Dynamics Picture of Magnetization Reversal 33
1.3.2 The Exactness of SW-Limit at Infinitely Large Dissipation 35
1.3.3 Critical Value of Damping Constant 37
1.3.4 Ballistic Reversal 39
1.4 Macro-spin Reversal with a Time-Dependent Magnetic Field 41
1.4.1 Strategy I: Field Following the Magnetization Motion 42
1.4.2 Strategy II: Synchronizing the Magnetization Motion with a Circularly Polarized Microwave 45
1.4.3 Theoretical Limits of Switching Field/Current and Optimal Reversal Pulses 49
1.5 Summary 56
2 CoreShell Magnetic Nanoclusters 59
2.1 Introduction 59
2.2 Experimental Studies of CoreShell Magnetic Clusters 61
2.2.1 Iron-Based (Fe--Au) Core--Shell Nanoclusters 62
2.2.2 Cobalt-Based Core--Shell Nanoclusters 68
2.2.2.1 Co--Pt Core--Shell Nanoalloys 68
2.2.2.2 Co@Au, Co@Pd, Co@Pt, and Co@Cu Nanoparticles 70
2.2.2.3 Pt--Co Core--Shell Nanoclusters 71
2.2.2.4 Co--Cu Core--Shell Nanoclusters 71
2.2.2.5 Co@Ag Core/Shell Nanoclusters 73
2.2.2.6 Co--Au Core--Shell Nanoclusters 73
2.2.3 Ni-Based Core--Shell Nanoclusters 74
2.2.3.1 Ni--Pd Core--Shell Nanoclusters 74
2.2.3.2 Ni--Ag Core--Shell Nanoclusters 74
2.2.3.3 Ni--Au Core--Shell Nanoclusters 75
2.3 Theoretical Studies of Bimetallic Magnetic CoreShell Nanoclusters 75
2.3.1 Iron-Based (Fe--Au) Core--Shell Nanoclusters 75
2.3.2 Cobalt-Based Core--Shell Nanoclusters 77
2.3.2.1 Co--Cu, Co--Ag Core--Shell Nanoclusters 77
2.3.2.2 Pd--Ag, Ni--Ag, Ni--Au, Co--Au Core--Shell Nanoclusters 78
2.3.3 Mn-Based CoreShell Nanoclusters: [Mn 13 @Au 20 ] -- 83
2.4 Summary 84
3 Designed Magnetic Nanostructures 90
3.1 Introduction 90
3.2 Structure, Chemistry, and Geometry 93
3.2.1 Synthesis of Supported Nanostructures 94
3.2.2 Case Study: Fe Clusters on Pt Surfaces 96
3.2.3 Structure of Embedded Clusters 98
3.2.4 Case Study: FePt Clusters in a Carbon Matrix 101
3.3 Anisotropy and Hysteresis 102
3.3.1 Surface and Interface Anisotropies 103
3.3.2 Hysteresis of Fe Clusters on Pt 104
3.3.3 Role of Heavy Transition Metals 106
3.3.4 Proteresis 108
3.4 Quantum-Mechanical Effects 108
3.4.1 Embedding from a Quantum-Mechanical Point of View 109
3.4.2 Exchange Interactions 110
3.4.3 Preasymptotic Coupling 113
3.4.4 Kondo Effect 115
3.4.5 Entanglement 116
3.5 Concluding Remarks 117
4 Superconductivity and Magnetism in Silicon and Germanium Clathrates 127
4.1 Introduction 127
4.2 Superconductivity in Si 46 Clathrates 130
4.3 Rattler Atoms and Narrow Bands 130
4.4 Superconducting Mechanism 133
4.5 Zintl Concept and Vacancies 137
4.6 Superconductivity in Other Clathrates 138
4.7 Magnetism 139
4.8 Conclusions 140
5 Neutron Scattering of Magnetic Materials 145
5.1 Introduction 145
5.2 Interaction of Neutrons and Materials: A Brief Presentation 146
5.3 Crystal Structure Investigation 148
5.3.1 Powder Diffraction 148
5.3.2 Single Crystal Diffraction 148
5.4 In Situ Neutron Diffraction 149
5.4.1 Thermodiffractometry: Crystallization of Amorphous Materials 150
5.4.2 In Situ Investigation of the Synthesis and Ordering of nanocrystalline FePt Alloys 151
5.4.3 Time-Resolved Neutron Diffraction Studies 152
5.4.3.1 Decomposition of Nd 2 Fe 14 B Under Hydrogen Atmosphere 153
5.4.3.2 Kinetics of Photoinduced Transformation 154
5.5 Magnetic Structure Determination 155
5.6 Magnetic Phase Transition 157
5.6.1 Magnetic Phase Transitions Studied by Powder Diffraction 157
5.6.2 Magnetic Phase Transitions Studied by Single Crystal Diffraction 159
5.7 Polarized Neutron Techniques 160
5.7.1 Uniaxial Polarization Analysis 160
5.7.2 Spherical Neutron Polarimetry 163
5.8 Small-Angle Neutron Scattering 163
5.9 Neutron Scattering on Magnetic Surfaces 166
5.10 Magnetic Excitations 168
5.11 Neutron Scattering Under Extreme Conditions 170
5.12 Conclusions 172
6 Tunable Exchange Bias Effects 180
6.1 Introduction 180
6.2 Electrically Tuned Exchange Bias 185
6.2.1 Electrically Tuned Exchange Bias with Magnetoelectrics 186
6.2.2 Electrically Tuned Exchange Bias with Multiferroics 189
6.2.3 Piezomagnetically and Piezoelectrically Tuned Exchange Bias 190
6.3 Magnetic Field Control of Exchange Bias 191
6.4 Training Effect in Exchange-Coupled Bilayers 195
6.4.1 Physical Background of Training Effects in Various Systems 195
6.4.2 Tuning the Training Effect 199
6.5 Conclusion 199
7 Dynamics of Domain Wall Motion in Wires with Perpendicular Anisotropy 205
7.1 Introduction 205
7.2 Basics of Field-Induced DW Motion in Pt/Co/Pt Ultra-Thin Films 207
7.2.1 Mechanisms of Magnetization Reversal in Pt/Co/Pt Trilayers 208
7.2.2 Different Regimes of DW Motion: The Role of Defects 209
7.3 Control and Detection of Single DW Motion in Magnetic Wires 212
7.3.1 Wires Nanofabrication and Injection of a Single Domain Wall 213
7.3.2 Electrical Methods to Detect DW Motion Along Tracks 214
7.4 Field-Induced DW Motion Along Wires: Role of Structural Defects 216
7.4.1 The Role of Edge Roughness on the Creep Regime in Co/Pt Films 216
7.4.2 The Role of Intrinsic Defects in Co/Ni Films 221
7.5 Control of the Pinning Potential 223
7.5.1 Ion Irradiation of Co/Pt Films: A Way to Reduce Intrinsic Structural Defects 224
7.5.2 A DW Propagating in a Hall Cross: An Artificial Pinning Potential 227
7.6 Current Induced DW Depinning 228
7.7 Conclusion 233
8 Magnetic Nanowires for Domain Wall Logic and Ultrahigh Density Data Storage 238
8.1 Domain Wall Propagation and Nucleation 238
8.2 Domain Wall Conduits 239
8.3 The NOT Gate and Shift Register Element 242
8.4 Data InputOutput 244
8.5 Using the Chirality of the Transverse Domain Wall 247
8.6 Potential Applications of Domain Wall Logic 250
8.7 Conclusion 253
9 Bit-Patterned Magnetic Recording: Nanoscale Magnetic Islands for Data Storage 256
9.1 Introduction 256
9.2 Theoretical Perspective of Bit-Patterned Recording 258
9.2.1 Island Addressability in Bit-Patterned Recording 259
9.2.2 Fabrication Tolerances of BPM 261
9.2.3 Thermal Constraints 262
9.2.4 Magnetostatic Interaction Fields Between Islands 264
9.2.5 BPM Designs for Tb/in 2 Densities 265
9.3 Optimization of the Magnetic Materials 267
9.3.1 Magnetic Characterization 268
9.3.2 Magnetic Switching-Field Distribution 271
9.3.3 Laminated Magnetic Media 273
9.3.4 Magnetic Trench Noise Reduction 274
9.4 Fabrication of Bit-Patterned Media 275
9.5 Generation of Master Patterns Beyond 1Tbit/in 2 via Guided Self-Assembly of Block Copolymer Domain Arrays 278
9.5.1 Ordering, Size Distribution, and Scalability: Patterned Media Requirements vs. Block Copolymer Fundamental Limitations 279
9.5.2 Approaches to Long-Range Orientational and Translational Order in Block Copolymer Templates 281
9.6 Write Synchronization 283
9.6.1 Requirements for Write Synchronization 284
9.6.2 Options to Achieve Write Synchronization 284
9.6.3 Timing Variations Observed in a Conventional Drive 285
9.6.4 Implementation of a Sector Synchronization System 287
9.7 Conclusion 289
10 The Magnetic Microstructure of Nanostructured Materials 294
10.1 Overview 294
10.2 Coarse-Grained Material and Amorphous Ribbons 296
10.3 Domains in Nanocrystalline Ribbons 300
10.3.1 Random Anisotropy Model 302
10.3.2 Interplay of Random and Uniaxial Anisotropies 306
10.3.3 Magnetization Process 311
10.4 Domains in Nanocrystalline Magnetic Films 315
10.5 Domains in Fine- and Nanostructured Permanent Magnets 319
10.6 Summary 323
11 Exchange-Coupled Nanocomposite Permanent Magnets 327
11.1 Introduction 327
11.2 Fundamental Aspects 328
11.2.1 The Early Models 329
11.2.2 The Soft Phase Effects 331
11.2.3 The Interface Effects 332
11.2.4 Coercivity Mechanisms 334
11.2.5 Characterization of Inter-phase Exchange Coupling 334
11.2.5.1 The ''Kink'' Method 335
11.2.5.2 Low-Temperature Measurements 335
11.2.5.3 Recoil Loop Measurements 336
11.2.5.4 0 M Method (Henkel Plot) 337
11.2.5.5 Element-Specific Measurements (Synchrotron Measurements) 338
11.3 Experimental Approaches 339
11.3.1 The Early Approaches 339
11.3.2 Nanoparticle Approaches 340
11.3.2.1 Chemical Synthesis of Nanoparticles 340
11.3.2.2 Salt-Matrix Annealing 342
11.3.2.3 Surfactant-Assisted Ball Milling 343
11.3.2.4 Gas-Phase Condensed Nanoparticles 343
11.3.2.5 Core/Shell Structured Nanoparticles 344
11.3.3 Fabrication of Nanocomposite Bulk Magnets 345
11.3.3.1 Warm Compaction 345
11.3.3.2 Spark Plasma Sintering Compaction 347
11.3.3.3 Dynamic Compaction 347
11.4 Work Toward Anisotropic Nanocomposite Magnets 349
12 High-Temperature Samarium Cobalt Permanent Magnets 354
12.1 Introduction 354
12.2 Physical Metallurgy and Crystal Structures 356
12.3 Coercivity Mechanism and the Development of High-Temperature 2:17-Type Magnets 360
12.3.1 The Sm(CoCu) 5 Cell Boundary Phase 360
12.3.2 Alloy Optimization 361
12.3.3 Stability at Operating Temperature 365
12.4 Microchemistry and Pinning Behavior in Sm 2 Co 17 -Type Magnets 366
12.4.1 Redistribution of Cu and Slow Cooling 366
12.4.2 Stability of Microchemistry 369
12.4.3 ''Anomalous'' Coercivity Behavior 372
12.5 Magnetic Domains and Coercivity 373
12.5.1 Analysis of Magnetic Microstructure 374
12.5.2 Domains and Processing Parameters 375
12.6 Non-equilibrium Processing Routes 379
12.6.1 Rapidly Quenched SmCo 5 /Sm 2 Co 17 Magnets 379
12.6.2 Mechanically Alloyed SmCo 5 /Sm 2 Co 17 Magnets 380
12.6.3 Hydrogen Disproportionated SmCo 5 and Sm 2 Co 17 Alloys 381
12.7 Acronyms 384
13 Nanostructured Soft Magnetic Materials 390
13.1 Introduction 390
13.2 Materials Development 393
13.2.1 Alloy Processing and Design 394
13.2.2 Phase Transformations 395
13.2.3 Annealing Techniques 398
13.3 Magnetic Performance 399
13.3.1 Exchange-Averaged Anisotropy 400
13.3.2 Intrinsic Magnetic Properties 401
13.3.3 Domain Structure 402
13.3.4 Hysteretic Losses 403
13.3.5 AC Properties 405
13.3.6 Thermomagnetics 406
13.4 Applications 406
13.4.1 Power Applications 408
13.4.2 Electromagnetic Interference Applications 409
13.4.3 Sensor Applications 410
13.5 Summary 410
14 Magnetic Shape Memory Phenomena 415
14.1 Introduction 415
14.2 Martensitic Transformation and Twinning 417
14.3 Modes of Magnetic Field-Induced Strain 418
14.3.1 Magnetostriction 419
14.3.2 Magnetic Field-Induced Phase Transformation 420
14.4 Magnetically Induced Structure Reorientation 421
14.5 The NiMnGa System 424
14.5.1 Compositional Dependence of Structure and Transformation 424
14.5.2 Martensitic Phases in Ni--Mn--Ga 426
14.5.3 Magnetic Properties of Ni--Mn--Ga 428
14.5.3.1 Magnetization Process in Twinned Martensitic Single Crystals 430
14.5.3.2 Magnetic Domain Structure 431
14.6 Twin Boundary Mobility 431
14.7 Energy Model for MIR 434
14.8 Angular Dependence 437
14.9 Reversible and Irreversible MIR Strain 438
14.10 Temperature Dependence of MIR 441
14.11 MIR in Polycrystals, Composites, and Films 443
14.12 Other Applications Based on MSM Alloys 445
14.13 Conclusion 446
15 Magnetocaloric Effect and Materials 456
15.1 Introduction 456
15.2 Theoretical Description of Magnetocaloric Effect 458
15.3 Experimental Determination of Magnetocaloric Effect 461
15.3.1 Direct Measurement of Adiabatic Temperature Change 461
15.3.2 Indirect Measurement of Entropy and Adiabatic Temperature Changes 461
15.4 Magnetocaloric Effect Associated with First-Order Phase Transition 462
15.4.1 MCE Due to an Idealized First-Order Phase Transition 462
15.4.2 MCE Due to a Non-Idealized First-Order Phase Transition 463
15.4.2.1 In the Vicinity of Curie Temperature 463
15.4.2.2 MCE Associated with Complex Magnetic Phase Transitions 465
15.5 Typical Materials with Giant Magnetocaloric Effect 466
15.5.1 LaFe 30x M x (M = Al, Si) Intermetallics 467
15.5.1.1 Generic Magnetic Properties 468
15.5.1.2 Spontaneous Magnetostriction of LaFe 130x Si x 471
15.5.1.3 Magnetocaloric effect in LaFe 13-x M x (M = Si, Al, and Co) 472
15.5.2 Gd 5 (Ge,Si) 4 and Related Compounds 487
15.5.3 Mn-Based Heusler Alloys 491
15.5.4 Mn-As-Based Compounds 493
15.6 Concluding Remarks 493
16 Spintronics and Novel Magnetic Materials for Advanced Spintronics 499
16.1 Introduction to Spintronics 499
16.2 Novel Magnetic Oxide Thin Films by Reactive Bias Target Ion Beam Deposition 503
16.2.1 Reactive Bias Target Ion Beam Deposition (RBTIBD) 504
16.2.2 Cr x V 10x O 2 Thin Films 505
16.2.3 Co x Ti 10x O 2 Thin Films 510
16.3 Diluted Ferromagnetic Ge 1x Mn x by Ion Implantation 513
17 Growth and Properties of Epitaxial Chromium Dioxide (CrO 2 ) Thin Films and Heterostructures 525
17.1 Density of States (DOS) of Half-Metallic CrO 2 and the Double Exchange Mechanism 525
17.2 Intrinsic Properties of Epitaxial CrO 2 Films 527
17.3 Influence of Strain on the Magnetic Properties of CrO 2 Thin Films 531
17.3.1 Film Growth on Atomically Smooth TiO 2 Substrates 531
17.3.2 Films Grown on As-Polished TiO 2 Substrates 535
17.4 CrO 2 -Based Heterostructures 537
17.4.1 Epitaxial SnO 2 Barrier Layer 539
17.4.2 Epitaxial RuO 2 Barrier Layer 542
17.4.3 VO 2 Barrier Layer 544
17.4.4 TiO 2 Barrier Layer 545
17.4.5 Cr 2 O 3 Barrier Layer 546
18 FePt and Related Nanoparticles 551
18.1 Introduction 552
18.2 Thermal Effects in Magnetic Nanoparticles 552
18.3 Magnetic Recording and the Superparamagnetic Limit 555
18.4 Chemical Synthesis and Shape Control of FePt and Related Nanoparticles 555
18.4.1 Synthesis 555
18.4.2 Shape Control 558
18.5 Prevention of Sintered Grain Growth During Annealing 559
18.5.1 FePt/MnO Core/Shell Nanoparticles 560
18.5.2 FePt/SiO 2 Core/Shell Nanoparticles 561
18.5.3 Salt Matrix Annealing 562
18.5.4 Flash Annealing 563
18.6 Effect of Metal Additives on Chemical Ordering and Sintered Grain Growth 564
18.7 Easy-Axis Orientation 566
18.7.1 Model of Easy-Axis Orientation 566
18.7.2 Easy-Axis Orientation Measurements 567
18.8 Composition Distribution 568
18.9 Anisotropy Distribution 569
18.10 Size Effect on Chemical Ordering 570
18.11 Summary and Conclusions 571
19 Magnetic Manipulation of Colloidal Particles 577
19.1 Introduction 577
19.2 Magnetic Manipulation of Particles 579
19.2.1 Deterministic and Brownian-Dominated Particle Systems 579
19.2.2 Material Properties 579
19.2.3 Magnetic Force 582
19.3 Deterministic Particle Manipulation 584
19.3.1 Substrate-Based Self-Assembly of Particles 584
19.3.2 Substrate-Based Transport and Separation 585
19.4 Brownian-Influenced Particle Manipulation 587
19.4.1 Magnetic and Nonmagnetic Particle Chains 587
19.4.2 Magnetic and Nonmagnetic Mixed Assemblies in Ferrofluid 590
19.4.3 Anisotropic Particle Alignment 590
19.5 Brownian-Dominated Manipulation of Particle Populations 592
19.5.1 Modeling Thermal Diffusion 593
19.5.2 Magnetic Particle Concentration 595
19.5.3 Nonmagnetic Particle Concentrations 598
19.5.4 Applications of Concentration Gradients 600
19.6 Conclusions and Outlook 600
20 Applications of Magnetic Nanoparticles in Biomedicine 605
20.1 Introduction 605
20.2 Nanoparticle Classification 606
20.3 Syntheses of SPIO Nanoparticles 606
20.3.1 Co-precipitation 607
20.3.2 Microemulsion 608
20.3.3 Thermal Decomposition 609
20.3.4 Alternative Methods 610
20.4 Surface Modifications of Magnetic Nanoparticles 610
20.4.1 Organic and Polymeric Stabilizers 611
20.4.1.1 Organic Stabilizers 611
20.4.1.2 Polymeric Stabilizers 611
20.4.2 Inorganic Molecules 612
20.5 Pharmacokinetics and Toxicology 613
20.6 Biomedical Applications of Magnetic Nanoparticles 617
20.6.1 Magnetic Resonance Imaging 617
20.6.1.1 Anatomical Imaging 617
20.6.1.2 Molecular Imaging and Targeting 622
20.6.1.3 Cellular Imaging and Tracking 623
20.6.2 Therapeutic Applications 626
20.6.2.1 Hyperthermia 626
20.6.2.2 Drug Delivery via Magnetic Targeting 629
20.7 Conclusion 630
20.8 Abbreviations 630
21 Nano-Magnetophotonics 641
21.1 Introduction 641
21.2 Magnetophotonic Crystals 642
21.2.1 1D MPCs Composed of Alternating Magnetic and Dielectric Layers 643
21.2.2 Microcavity-Type 1D MPCs 647
21.2.3 Photonic Band Structure and Eigenmodes of 2D MPCs 649
21.2.4 Faraday Rotation of Three-Dimensional Magnetophotonic Crystals 651
21.2.5 Nonlinear Optical and Magneto-Optical Properties 654
21.2.6 Conclusion 655
21.3 Magnetorefractive Effect in Nanostructures 655
21.3.1 Magnetorefractive Effect in Nanostructures and Manganites 656
21.3.2 Enhancement of the MRE in Magnetophotonic Crystals 658
21.3.3 Conclusion 661
21.4 Plasmon-Enhanced Magneto-Optical Responses 661
21.4.1 Garnet--Noble Metal Nanocomposites 662
21.4.2 Metal--Garnet Structures Supporting Transmission Resonances 665
21.4.3 Conclusion 667
22 Hard Magnetic Materials for MEMS Applications 674
22.1 An Introduction to MEMS 674
22.1.1 What Are MEMS? 674
22.1.2 How Are MEMS Made? 675
22.2 Magnetic MEMS 675
22.2.1 Downscaling Magnetic Systems 676
22.2.2 Prototype Magnetic MEMS 678
22.3 Permanent Magnets 679
22.4 Fabrication of -Magnets: Top-Down Routes 680
22.4.1 Bulk Processed Magnets 681
22.4.1.1 Machining of Sintered Magnets 681
22.4.1.2 Mechanical Deformation 681
22.4.2 Bulk Processed Hard Magnetic Powders 682
22.4.2.1 Bonded Powder Techniques 682
22.4.2.2 Non-Bonded Powder Techniques 684
22.5 Fabrication of Thick Hard Magnetic Films 684
22.5.1 Electrodeposition 685
22.5.2 Sputtering 685
22.5.2.1 High-Rate Triode Sputtering of NdFeB Films 686
22.5.2.2 High-Rate Triode Sputtering of SmCo Films 687
22.5.3 Pulsed Laser Deposition (PLD) 688
22.6 Micro-Patterning of Thick Hard Magnetic Films 689
22.6.1 Topographically Patterned Films 689
22.6.1.1 Deposition of RE-TM Films onto Patterned Substrates 690
22.6.1.2 Wet Etching of RE-TM Films 692
22.6.1.3 Planarization of NdFeB Films 692
22.6.2 Crystallographically Patterned Films 692
22.7 Conclusions and Perspectives 693
23 Solid-State Magnetic Sensors for Bioapplications 697
23.1 Introduction 697
23.2 Magnetic Sensors Based on GMR Effect 699
23.2.1 GMR Sensors 701
23.2.2 Spin Valve Sensors 705
23.2.3 GMR and Spin Valve Sensors for Detection of Nanoparticles 707
23.3 MTJ Sensors 708
23.4 Sensors Based on AMR Effect 711
23.4.1 AMR Ring Sensors 712
23.4.2 Planar Hall Effect Sensors 712
23.5 Hall Effect Sensors 714
23.6 GMI Sensors 717
23.7 Conclusions 719
Index 723