ALBERTO BOLLERO REAL

CONTENTS
Synopsis / Zusammenfassung
Notation and quantities
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vii
1. Introduction 1
2. Magnetism of R-T intermetallic compounds 4
2.1. Hysteresis loop 4
2.2. Magnetic properties 6
2.2.1. Magnetic moments 6
2.2.2. Exchange interactions 8
2.2.3. Anisotropy 10
2.2.4. Magnetic domains 11
2.2.5. Origin of coercivity 13
3. The exchange-coupling mechanism 16
3.1. Models 17
3.1.1. Single-phase nanocrystalline magnets 17
3.1.2. Two-phase nanocomposite magnets 19
3.2. Wohlfarth’s relation and Henkel plot 20
3.3. Magnetisation reversal processes in nanocomposite magnets 22
3.3.1. Recoil loops and “exchange-spring” magnet behaviour 22
3.3.2. Intergrain interactions: δJ-plot 23
3.3.3. Nucleation field 23
3.4. Development of exchange-coupled nanocrystalline magnets 24
4. Systems under investigation 28
4.1. NdFeB 28
4.2. NdCoB 30
4.3. PrFeB 31
5. Experimental details 34
5.1. Nanocrystalline powder processing 34
5.1.1. Melt-spinning 34
5.1.2. High energy ball milling 35
5.1.3. Reactive milling in hydrogen 36
5.1.4. Hot deformation 38
5.2. Structural characterisation 38
5.2.1. Differential scanning calorimetry 38
5.2.2. X-ray diffraction 39
5.2.3. Electron microscopy 41
5.3. Characterisation of magnetic properties 41
5.3.1. Vibrating sample magnetometer 41
5.3.2. Curie temperature measurements 42
6. Decoupled magnets: (Nd,Pr)-based magnets 43
6.1. Thermal characterisation 43
6.1.1. Starting alloys 43
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