Magnetism and Structure in Functional Materials (eBook)

Preface 7
Contents 9
List of Contributors 14
1 Complex Functional Materials 17
2 Spin, Charge, and Lattice Coupling in Multiferroic Materials 19
2.1 Introduction 19
2.2 Order Parameters and Multiferroics 21
2.3 Strain Tensor and Elastic Compatibility 22
2.4 Inhomogeneities in Ferroelastics 29
2.5 Inhomogeneities in Multiferroic Oxides 32
2.6 Charge and Spin as Local Stresses and Transition Temperatures 34
2.7 Summary and Further Work 37
References 38
3 Disorder in Magnetic and Structural Transitions: Pretransitional Phenomena and Kinetics 43
3.1 Introduction 43
3.2 Disorder Distribution 44
3.3 Transition Kinetics 53
3.4 Conclusion 61
References 62
4 Huge Magnetoresistance in Association with Strong Magnetoelastic Effects 65
4.1 Introduction 65
4.2 Magnetic–Crystallographic Transformations 66
4.3 Moment Instabilities and Spin Fluctuations 69
4.4 Metal–Insulator Transitions 73
4.5 Charge/Orbital Instabilities 81
4.6 Conclusion 86
References 87
5 Interplay of Spin, Charge, and Lattice in CMR Manganites and HTSC Cuprates 91
5.1 Introduction 91
5.2 Stability of Polaronic Phase in the CMR Manganites 92
5.3 Stability of Spin–Charge Stripes in the Cuprates 99
5.4 Electron–Phonon Coupling and Mechanism of Superconductivity in the Cuprates 100
5.5 Conclusions 105
References 106
6 Neutron Scattering Studies of Anomalous Phonon Behavior in Functional Materials 109
6.1 Introduction 109
6.2 Neutron Scattering 110
6.3 Phonon Anomalies 111
6.4 Phonon Anomalies in the Manganites 115
6.5 Phonon Anomalies in High Temperature Superconductors 116
6.6 Ferromagnetic Shape Memory Alloys 118
6.7 Summary 126
References 127
7 The Structures and Transformation Mechanism in the Ferromagnetic Shape Memory Alloy Ni2MnGa 129
7.1 Introduction 129
7.2 The Crystal Structure of the Cubic Austenite Phase 129
7.3 Bulk Magnetic Properties 132
7.4 Spin Dynamics 134
7.5 Paramagnetic Response 134
7.6 Inelastic Neutron Scattering 135
7.7 Neutron Diffraction 137
7.8 Pre-Martenstic Phase 138
7.9 The Martensitic Phase 142
7.10 Structural and Magnetic Phase Diagram 143
7.11 Mechanism 145
7.12 Martensitic Twinning in Ni2MnGa 146
7.13 Non Stoichiometric Samples 149
7.14 Electron Concentration 151
7.15 Polarised Neutron Scattering 152
7.16 Conclusion 153
References 154
8 Imaging Techniques in Magnetoelastic Materials 157
8.1 Introduction 157
8.2 Lorentz Image Formation Theory 157
8.3 Applications of LTEM to Ferromagnetic Shape Memory Alloys 164
8.4 Summary 172
References 172
9 A Way to Search for Multiferroic Materials with "Unlikely” Combinations of Physical Properties 175
9.1 Introduction 175
9.2 Single Phase Multiferroics 176
9.3 Basic Idea 176
9.4 Lattice Parameter Sensitivity 177
9.5 What Makes Big First Order Phase Transformations Reversible? 178
9.6 Specific Relationships Among Lattice Parameters for a High Degree of Reversibility 185
9.7 Tuning Lattice Parameters to Satisfy Two of the Proposed Conditions in the NiTiCuPd System 187
9.8 Further Comparisons with Experiment 188
9.9 Summary and Outlook: A General Method for Seeking New Classes of Functional Materials 190
References 190
10 Invar and Anti-Invar: Magnetovolume Effects in Fe- Based Alloys Revisited 193
10.1 Introduction 193
10.2 Invar 193
10.3 From Invar to Anti-Invar 197
10.4 Allotropy of Pure Fe 200
10.5 Ground State Properties of Invar and Anti-Invar 203
10.6 Pressure Experiments: Evidence for High Spin to Low Spin State Transitions 205
10.7 HS–LS Transitions in a Microscopic Picture 208
10.8 Questions and Outlook 211
References 212
11 Magnetocaloric Effect Associated with Magnetostructural Transitions 215
11.1 Introduction 215
11.2 Magnetic Cooling or Why Having a Strong Magnetocaloric Effect in a Weak Magnetic Field Makes a Difference? 215
11.3 Gd5(Si4 xGex) System and the Giant Magnetocaloric Effect 218
11.4 Altering Crystal Structures with a Magnetic Field 222
11.5 To What Extent a Structural Change Enhances the Giant Magnetocaloric Effect? 230
11.6 Conclusions 235
References 236
12 Entropy Change and Magnetocaloric Effect in Magnetostructural Transformations 239
12.1 Introduction 239
12.2 Multiscale Origin of the MCE in Ni–Mn–Ga Alloys 241
12.3 Direct Determination of the Entropy Change at a First- Order Transformation 245
12.4 Magnetostructural Transformation in Gd– Si– Ge Alloys 246
12.5 Conclusions 251
References 251
13 Functional Magneto-Structural Materials: Summary and Perspectives 253
References 259
Index 263