Contents
Preface
Chapter 1 Millenniums of Permanent Magnets: From Compasses to Rare-earth Magnets 1
References 5
Chapter 2 Coercivity Mechanisms in Nanostructured Permanent Magnets 7
2.1 Introduction 8
2.2 Hysteresis loops and a survey of various coercivity mechanisms 10
2.2.1 Hysteresis loops 10
2.2.2 Coherent rotation and domain wall motion 12
2.2.3 Various modes of nucleation and nucleation expansion 14
2.2.4 Numerical approaches and more advanced models 16
2.3 Interface-pinning of well-oriented permanent magnetic systems 18
2.3.1 Basic formulation 18
2.3.2 Comparison of nucleation and self-pinning fields 19
2.3.3 Experimental evidence and comparison with other theories 25
2.4 Discussions and conclusions 26
2.4.1 Single-phase versus two-phases 26
2.4.2 Pinning versus nucleation 27
2.4.3 Size e.ect and grain boundary enhancement 29
2.4.4 Conclusions 30
References 31
Chapter 3 Sm-Co High-Temperature Permanent Magnet Materials 36
3.1 Introduction 36
3.2 Historical review of development of Sm-Co permanent magnets 38
3.3 Phase diagram and crystal structures 40
3.4 Intrinsic magnetic properties of R-Co compounds 42
3.5 Sm-Co permanent magnets capable of operating up to 300 46
3.6 High-temperature Sm2(Co, Fe, Cu, Zr)17-type magnets capable of operating up to 550 51
3.6.1 Effects of compositions on high-temperature intrinsic coercivity of Sm-TM permanent magnets 52
3.6.2 New high-temperature Sm2(Co, Fe, Cu, Zr)17-type magnets 53
3.6.3 Long-term thermal stability of new high-temperature permanent magnets 56
3.6.4 Abnormal temperature dependence of intrinsic coercivity 57
3.7 Thermal stability, temperature coeffcient, and modeling of temperature-compensated magnets 57
3.7.1 Reversible and irreversible flux density loss 57
3.7.2 Temperature coeffcient 59
3.7.3 Modeling of temperature-compensated magnets 62
3.8 Nanograin structure, nanocrystalline, and nanocomposite Sm-Co magnetic materials 65
3.9 Other Sm-Co permanent magnet materials 72
3.10 Prospects of future rare earth permanent magnet materials 73
3.11 Conclusions 76
References 77
Chapter 4 Ternary Fe-rich R-Fe-M Intermetallics with the ThMn12-type Structure and Their Interstitial Compounds 82
4.1 Introduction 82
4.2 Part one: Ternary Fe rich 1-12 compounds 85
4.2.1 Structural and magnetic properties of Y(Mn1.xFex)12 which is the first synthesis of Fe-rich 1-12 compounds 85
4.2.2 Structural and magnetic properties of RFe12.xMx 90
4.2.3 Structural and magnetic properties of RTiFe11 in comparison with RTiCo11 and YTi(Fe1.xNix)11 90
4.3 Part two: Interstitial nitrogen atom e.ect on the 1-12 compounds and its applications 108
4.3.1 Interstitial nitrogen atom e.ect on the 1-12 compounds 108
4.3.2 Interstitial hydrogen (or carbon) atom e.ect on the 1-12 compounds 116
4.3.3 Development of novel permanent magnets based on R(Fe,M)12Nx 121
4.4 Concluding remarks 129
References 130
Chapter 5 Mn-based Permanent Magnets 134
5.1 Introduction 135
5.2 Mn-Al hard magnetic phase 136
5.3 MnBi hard magnetic materials 147
5.4 MnxGa magnetic materials 157
5.5 Summary 164
References 164
Chapter 6 Anisotropic Nanocomposite Soft/Hard Multilayer Magnets 169
6.1 Introduction 170
6.2 The anisotropic Nd2Fe14B based nanocomposite multilayer magnets 171
6.3 Anisotropic SmCo5 based nanocomposite permanent multilayer magnets 204
6.4 Anisotropic rare-earth free based nanocomposite permanent multilayer magnets 211
References 218
Chapter 7 Nanocrystalline and Nanocomposite Permanent Magnets by Melt Spinning Technique 223
7.1 Melt-spinning technique 224
7.2 Uniqueness in melt-spun materials 227
7.2.1 Cooling control 229
7.2.2 Amorphization and crystallization 232
7.2.3 Phase formation 234
7.2.4 Consolidation 236
7.3 Melt-spun materials 241
7.3.1 Single-phase nanocrystalline magnets 241
7.3.2 Nanocomposite magnets 266
7.3.3 Precipitation-hardening ribbons 288
7.4 Magnetic phenomena in melt-spun magnets 300
7.4.1 Single-phase magnetic behavior 301
7.4.2 Remanence enhancement 303
7.4.3 Henkel plot 306
7.4.4 Recoil loop 311
7.4.5 First-order reversal curve 317
7.4.6 Coercivity and microstructure parameters 320
7.4.7 Reversible and irreversible magnetization 323
7.5 Summary and outlook 325
References 326
Chapter 8 Grain Boundary Restructuring and La/Ce/Y Application in Nd-Fe-B Magnets 339
8.1 Introduction 340
8.2 Grain boundary restructuring of Nd-Fe-B sintered magnets 341
8.2.1 Fundamentals of grain boundary restructuring 341
8.2.2 (Pr, Nd)32:5Fe62:0Cu5:5 restructuring: High corrosion-resistant Nd-Fe-B 342
8.2.3 Dy71:5Fe28:5 restructuring: High-coercivity Nd-Fe-B 350
8.3 Application of high-abundant La/Y/Ce in Nd-Fe-B magnets 355
8.3.1 La-Ce co-substitution 356
8.3.2 Y-Ce co-substitution for Nd 381
8.3.3 Effect of REFe2 on microstructure and magnetic properties of (Nd, Ce)-Fe-B sintered magnets 387
8.4 Summary and perspectives 398
References 399
Chapter 9 Rare Earth Permanent Magnets Prepared by Hot Deformation Process 404
9.1 Introduction 405
9.2 Effect of preparation parameters on HD magnets 407
9.2.1 HP temperature 408
9.2.2 HD temperature 409
9.2.3 Deformation degree 410
9.2.4 Strain rate 412
9.2.5 Inhomogeneity of microstructure in HD magnet 413
9.2.6 Influence of chemical composition 414
9.3 Coercivity enhancement for HD Nd-Fe-B magnets 417
9.3.1 Coercivity mechanism of HD Nd-Fe-B magnets 417
9.3.2 Coercivity enhancement of hot-deformed Nd-Fe-B magnets 418
9.3.3 Discussion on the coercivity enhancement of HD Nd-Fe-B magnets 423
9.4 HD nanocomposite Nd-Fe-B magnets 425
9.4.1 Nanocomposite magnets prepared by Nd-lean powders 426
9.4.2 Nanocomposite magnets prepared by the co-doping technique 429
9.4.3 The deformability enhancement of nanocomposite magnets by introducing rare-earth-rich liquid phase 430
9.5 Radially oriented Nd-Fe-B ring magnet prepared by backward extrusion method 432
9.5.1 Texture evolution in backward extrusion of NdFeB ring magnet 434
9.5.2 Magnetic performance improvement of backward-extruded NdFeB RM 436
9.5.3 Solution for tangential crack in NdFeB RM 437
9.6 Physical properties of HD Nd-Fe-B magnets 440
9.6.1 Mechanical properties of HD Nd-Fe-B magnet 440
9.6.2 Electrical properties of HD Nd-Fe-B magnet 443
References 445
Chapter 10 Progress in Recycling of Nd-Fe-B Sintered Magnet Wastes 451
10.1 Introduction 452
10.2 Recycling techniques for bulk Nd-Fe-B sintered magnet wastes 454
10.2.1 Introduction to the recycling techniques 454
10.2.2 Magnet-magnet techniques 455
10.2.3 Magnet-powder technologies 460
10.3 Overall properties of the recycled Nd-Fe-B sintered magnets 464
10.3.1 Thermal stability of the recycled magnets 464
10.3.2 Chemical stability of the recycled magnets 465
10.3.3 Mechanical properties of the recycled magnets 468
10.4 Recycling of bulk Nd-Fe-B sintered wastes at mass production level 468
10.5 Concluding remarks and perspectives 471
References 472