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《磁性材料的新巡游电子模型（英文版）》介绍几个长期困扰磁学界的难题，以及探索解决这些难题的一套全新磁性材料磁有序模型体系，包括关于典型磁性氧化物的巡游电子模型、关于典型磁性金属的新巡游电子模型，以及涵盖典型磁性金属和氧化物的磁有序能来源的外斯电子对模型。应用这三个模型研究典型磁性材料，不仅可以解释利用传统模型可以解释的实验现象，对一些长期困扰磁学界的难题也给出了合理解释。这三个模型的物理意义清晰，对于理解磁性材料的磁有序现象和设计新型磁性材料将有所帮助。

Contents

1 Introduction 1

References 3

2 Electron Shell Structure of Free Atoms and Valence Electrons in Crystals 5

2.1 Electron Shell Structure of Free Atoms 5

2.2 A Simple Introduction to Classical Crystal Binding Theory for Typical Magnetic Materials 6

2.3 Effective Radii of Ions in Crystals 8

2.4 Electron Binding Energy Originating from Ions in Crystals 9

References 11

3 A Simple Introduction to Basic Knowledge of Magnetic Materials 13

3.1 Classification of Matter Based on Magnetic Properties 13

3.2 Magnetic Domain and Domain Wall 16

3.3 Basic Parameters of Magnetic Materials 18

3.4 Magnetic Ordering Models in Conventional Ferromagnetism 21

References 24

4 Difficulties Faced by Conventional Magnetic Ordering Models 25

4.1 Disputes Over the Cation Distributions in Mn and Cr Spinel Ferrites 25

4.1.1 Normal， Inverse， and Mixed Spinel Structure 25

4.1.2 Magnetic Moments of 3d Transition Metal Ions 27

4.1.3 Magnetic Ordering of CrFe204 and MnFe204 27

4.2 Difficulties in Describing the Observed Magnetic Moments of Perovskite Manganites 31

4.3 Relationship Between Magnetic Moment and Resistivity in Typical Magnetic Metals 38

4.4 Puzzle for the Origin of Magnetic Ordering Energy 38

References 39

5 02p Itinerant Electron Model for Magnetic Oxides 43

5.1 A Simple Introduction to Early Investigations of Ionicity 43

5.2 Study of the Ionicity of Spinel Ferrites 45

5.2.1 Quantum-Mechanical Potential Barrier Model Used to Estimate Cation Distributions 46

5.2.2 Study of the Ionicity of Group II-VI Compounds Using the Quantum-Mechanical Potential Barrier Model 47

5.2.3 Study of Ionicity of Spinel Ferrite Fe3o4 48

5.2.4 Estimation of the Ionicity of Spinel Ferrites M3O4 Using the Quantum- Mechanical Potential Barrier Model 50

5.3 Experimental Studies of O 2p Holes in Oxides 51

5.3.1 O 2p Hole Studies Using Electron Energy Loss Spectroscopy 52

5.3.2 Several Other Experimental Investigations for O 2p Holes 54

5.4 Study of Negative Monovalent Oxygen Ions Using X-Ray Photoelectron Spectra 54

5.4.1 Study of Ionicity of BaTiC>3 and Several Monoxides Using O Is XPS 55

5.4.2 Effect of Argon Ion Etching on the O Is Photoelectron Spectra of SrTio3 60

5.5 O 2p Itinerant Electron Model for Magnetic Oxides (IEO Model) 70

5.6 Relationship Between the IEO Model and the Conventional Models 75

References 79

6 Magnetic Ordering of Typical Spinel Ferrites 81

6.1 Method Fitting Magnetic Moments of Typical Spinel Ferrites 81

6.1.1 X-ray Diffraction Analysis 82

6.1.2 Magnetic Property Measurements 84

6.1.3 Primary Factors that Affect Cation Distributions 85

6.1.4 Fitting the Magnetic Moments of the Samples 88

6.1.5 Discussion on Cation Distributions 91

6.2 Cation Distribution Characteristics in Typical Spinel Ferrites 94

References 100

7 Experimental Evidences of the IEO Model Obtained from Spinel Ferrites 101

7.1 Additional Antiferromagnetic Phase in Ti-Doped Spinel Ferrites 101

7.1.1 X-ray Diffraction Spectra of the Samples 102

7.1.2 X-ray Energy Dispersive Spectra of the Samples 104

7.1.3 Magnetic Measurements and Analysis of the Results 106

7.1.4 Cation Distributions of the Three Series of Ti-Doped Samples 108

7.1.5 Magnetic Ordering of Spinel Ferrites TicM1_xFe204 (M = Co， Mn) 115

7.2 Amplification of Spinel Ferrite Magnetic Moment Due to Cu Substituting for Cr 116

7.2.1 X-ray Energy Dispersive Spectrum Analysis 116

7.2.2 X-ray Diffraction Analysis 117

7.2.3 Magnetic Measurement and Magnetic Moment Fitting Results 118

7.3 Unusual Infrared Spectra of Cr Ferrite 122

7.3.1 Infrared Spectra of Spinel Ferrites M￥q2Oa (M=Fe， Co， Ni， Cu， Cr) 123

7.3.2 Dependency of the Peak Position V2 on the Magnetic Moment (Xm2) of Divalent M Cations in MFe2O4(M= Fe， Co， Ni， Cu， Cr) 125

7.3.3 Infrared Spectra of and CoCrxFe2-x04 126

References 126

8 Spinel Ferrites with Canted Magnetic Coupling 129

8.1 Spinel Ferrites with Fe Ratio Being Less Than 2.0 Per Molecule 129

8.2 Spinel Ferrites Containing Nonmagnetic Cations 132

8.2.1 Disputation of Nonmagnetic Cation Distribution 133

8.2.2 Fitting Sample Magnetic Moments 136

8.2.3 Discussion on Cation Distributions 137

References 145

9 Magnetic Ordering and Electrical Transport of Perovskite Manganites 147

9.1 Ferromagnetic and Antiferromagnetic Coupling in Typical Perovskite Manganites 147

9.1.1 Crystal Structure and Magnetic Measurement Results of Lai-xSrxMnOs Polycrystalline Powder Samples 147

9.1.2 Study of Valence and Ionicity of Lai-xSrxMn03 150

9.1.3 Fitting of the Curve of the Magnetic Moment Versus Sr Ratio for Lai-xSrxMn03 152

9.2 Spin-Dependent and Spin-Independent Electrical Transport of Perovskite Manganites 155

9.2.1 A Model with Two Channels of Electrical Transport for ABO3 Perovskite Manganites 156

9.2.2 Fitting the Curves of Resistivity Versus Test Temperature o

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Chapter 1 Introduction

　　One of the oldest applications of magnetic materials is the use of compass. In modem times， the applications of magnetic materials have benefited many fields， such as aviation， spaceflight，military affairs， radio， television， communication， and medicine， in the form of magnetic memory devices， magnets， transformers， and microwave devices.

　　However， some of the challenging problems on magnetic ordering phenomena have not been reasonably explained because of the lack of phenomenological expression of the magnetic ordering energy， or the energy of the Weiss molecular field. In 1907， Weiss proposed the presence of small regions in magnetic materials called magnetic domains. In each magnetic domain， atomic magnetic moments arrange in a certain order subjected to a “molecular field”. Magnetic domains have been observed in many experimental studies. However， the origin of the molecular field is yet to be explained satisfactorily.

　　Several different models for the magnetic ordering mechanism were introduced in the textbooks [14]，including phenomenological spontaneous magnetization theory， exchange interaction theory for spontaneous magnetization， spin-wave theory， and metal energy band theory. These theories are based on different assumptions and rely on different theoretical systems. Since they fail to explain several experimental phenomena， developing ferromagnetism theory is challenging.

　　In classical ferromagnetism， the origin of magnetic ordering energy was explained by using exchange interactions of electrons between ions， called direct exchange interaction in magnetic metals and alloys， superexchange (SE) interaction for the anti？ferromagnetic coupling between magnetic cations in an oxide， and double-exchange (DE) interaction for the ferromagnetic coupling between magnetic cations in an oxide. Because nearly a thousand times difference for magnetic ordering energy between estimated (using the Curie temperature) and calculated (using classical electromagnetism model) values exist， the origin of magnetic ordering energy is considered to be a pure quantum-mechanical effect， independent of the classical electromagnetism model. However， magnetic material calculation using the density functional theory (DFT) based on quantum mechanics is challenging because the expression to calculate the magnetic ordering energy has not been developed.

　　No report has addressed the valence electron spectrum when the classical ferro？magnetism models were proposed before 1960. Since the 1970s， many studies have reported electron spectra of magnetic materials，and an improved understanding of the electrical transport mechanism for magnetic perovskite manganites was provided.

　　The magnetic DE interaction was firstly used to explain the ferromagnetic coupling between Mn cations in ABO3 perovskite manganites， in particular， Lai_xSrxMn03. In the classical view [5，6]， all oxygen anions are assumed to be O2- in these materials. With increasing Sr2 ratio (jc)， an equal number of Mn4+ ions exist in the system. The DE interaction of 3d electrons between Mn3+ and Mn4+ ions mediated by O2- ions， was used to explain the magnetic ordering and the electrical transport phenomena in Lai_xSrxMn03.

　　However， based on the electron energy loss spectra and other electron spectrum experimental results， Alexandrov et al. [7] pointed out that the DE model contradicts these experimental results， which clearly showed that the current carriers are oxygen p holes rather than d electrons of ferromagnetic manganites. Studies have shown that O1- ions may constitute 30% or more of oxygen ions in oxides. The outer electron shell of an O1- ion exists ap hole， which affects the magnetic and electrical transport properties of oxides. In fact， the effect of oxygen p holes was accurately considered in the investigation of superconductor oxides [8] but has not been widely accepted in studies concerning magnetic oxides.

　　Our group cooperated with Professors Wu and Hu of State Key Laboratory of Magnetism， Institute of Physics， Chinese Academy of Sciences， and published a series of articles about the new magnetic ordering models， including a review article in Physics Reports [9] titled “Three models of magnetic ordering in typical magnetic materials”. These models include an O 2p itinerant electron model for magnetic oxides (IEO model) [10，11]， a new itinerant electron model for magnetic metals (IEM model) [12]，and a Weiss electron-pair (WEP) model for the origin of magnetic ordering energy [13]. By using the IEO model that replaces the SE and DE models， the magnetic structures of not only Co-， Ni-，or Cu-doped spinel ferrites but also Cr-， Mn-， or Ti-doped spinel ferrites could be explained， moreover， the dependence of the magnetic moments on the Sr ratio in perovskite manganites (such as Lai_文SrxMno3) can be explained， for which there have been many ongoing disputes regarding the cation distributions of these materials

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书籍介绍

《磁性材料的新巡游电子模型（英文版）》介绍几个长期困扰磁学界的难题，以及探索解决这些难题的一套全新磁性材料磁有序模型体系，包括关于典型磁性氧化物的巡游电子模型、关于典型磁性金属的新巡游电子模型，以及涵盖典型磁性金属和氧化物的磁有序能来源的外斯电子对模型。应用这三个模型研究典型磁性材料，不仅可以解释利用传统模型可以解释的实验现象，对一些长期困扰磁学界的难题也给出了合理解释。这三个模型的物理意义清晰，对于理解磁性材料的磁有序现象和设计新型磁性材料将有所帮助。