Magnetism Molecules to Materials IV

Magnetism
 
Author:
Joel S. Miller & Marc Drillon
Publisher: Wiley-VCH
ISBN No: 3-527-60069-8
Release at: 2002
Pages: 491
Edition:
First Edition
File Size: 11 MB
File Type: pdf
Language: English



Description of Magnetism Molecules to Materials IV


The development, characterization, and technological exploitation of new materials, particularly as components in ‘smart’ systems, are key challenges for chemistry and physics in the next millennium. New substances and composites including nanostructured materials are envisioned for innumerable areas including magnets for the communication and information sector of our economy. 

Magnets are already an important component of the economy with worldwide sales of approximately $30 billion, twice that of the sales of semiconductors. Hence, research groups worldwide are targeting the preparation and study of new magnets especially in combination with other technologically important properties, e. g., electrical and optical properties.

Content of Magnetism Molecules to Materials IV



1 Bimetallic Magnets: Present and Perspectives1
1.1 Introduction1
1.2 Bimetallic Magnetic Materials Derived
from Oxamato-based Complexes2
1.2.1 Dimensionality and Magnetic Properties 2
1.2.2 Modulation of the Magnetic Properties17
1.2.3 Dimensionality Modulation by a
Dehydration-Polymerization Process 20
1.2.4 Alternative Techniques for the Studies of Exchange-coupled Systems26
1.3 Bimetallic Magnets Based on Second and Third-row Transition Metal Ions28
1.3.1 Examples of Ru(III)-based Compounds28
1.3.2 Mo, Nb, and W-cyanometalate-based Magnets 31
1.3.3 Light-induced Magnetism36
1.4 Concluding Remarks37
References38

2 Copper(II) Nitroxide Molecular Spin-transition Complexes41
2.1 Introduction 41
2.2 Nitroxide Free Radicals as Building Blocks
for Metal-containing Magnetic Species. 42
2.2.1 Electronic Structure 43
2.2.2 Coordination Properties. 43
2.3 Molecular Spin Transition Species46
2.3.1 Discrete Species46
2.3.2 One-dimensional Species50
2.4 Conclusion. 61
References62

3 Theoretical Study of the Electronic Structure of and Magnetic Interactions in Purely Organic Nitronyl Nitroxide Crystals ... 65
3.1 Introduction 65
3.2 Electronic Structure of Nitronyl Nitroxide Radicals. 68
3.2.1 Fundamentals68
3.2.2 Ab-initio Computation of the Electronic Structure
of Nitronyl Nitroxide Radicals. 73
3.2.3 Spin Distribution in Nitronyl Nitroxide Radicals 78
3.3 Magnetic Interactions in Purely Organic Molecular Crystals88
3.3.1 Basics of the Magnetism
in Purely Organic Molecular Crystals. 88
3.3.2 The McConnell-I Mechanism:
A Rigorous Theoretical Analysis 90
3.3.3 Theoretical Analysis
of Through-space Intermolecular Interactions 94
3.3.4 Experimental Magneto-structural Correlations 102
3.3.5 Theoretical Magneto-structural Correlations. 105
References113

4 Exact and Approximate Theoretical Techniques
for Quantum Magnetism in Low Dimensions119
4.1 Introduction 119
4.2 Exact Calculations121
4.3 Applications to Spin Clusters 125
4.4 Field-Theoretic Studies of Spin Chains. 129
4.4.1 Nonlinear σ-model 130
4.4.2 Bosonization133
4.5 Density Matrix Renormalization Group Method137
4.5.1 Implementation of the DMRG Method139
4.5.2 Finite Size DMRG Algorithm140
4.5.3 Calculation of Properties in the DMRG Basis 142
4.5.4 Remarks on the Applications of DMRG142
4.6 Frustrated and Dimerized Spin Chains. 144
4.7 Alternating (S1, S2) Ferrimagnetic Spin Chains148
4.7.1 Ground State and Excitation Spectrum149
4.7.2 Low-temperature Thermodynamic Properties. 155
4.8 Magnetization Properties of a Spin Ladder 160
References168

5 Magnetic Properties of Self-assembled [2 × 2] and [3 × 3] Grids173
5.1 Introduction 173
5.2 Polytopic Ligands and Grid Complexes 174
5.2.1 [2 × 2] Ligands175
5.2.2 Representative [2 × 2] Complexes 176
5.2.3 [3 × 3] Ligands and their Complexes. 187
5.3 Magnetic Properties of Grid Complexes 189
5.3.1 [2 × 2] Complexes . 189
5.3.2 [3 × 3] Complexes 191
5.3.3 Magnetic Properties of [2 × 2] and [3 × 3] Grids 192
5.3.4 Potential Applications of Magnetic Grids
to Nanoscale Technology201
References202

6 Biogenic Magnets ... 205
6.1 Introduction 205
6.1.1 Magnetotactic Bacteria 205
6.1.2 Magnetosomes206
6.1.3 Magnetite Magnetosomes207
6.1.4 Greigite Magnetosomes. 208
6.2 Magnetic Properties of Magnetosomes. 209
6.2.1 Magnetic Microstates and Crystal Size. 209
6.2.2 Single-domain (SD) and Multi-domain (MD) States. 211
6.2.3 Superparamagnetic (SPM) State 211
6.2.4 Theoretical Domain Calculations: Butler–Banerjee Model. 213
6.2.5 Local Energy Minima and Metastable SD States:
Micromagnetic Models 214
6.2.6 Magnetic Anisotropy of Magnetosomes215
6.2.7 Magnetosome Chains 217
6.2.8 Magnetic Properties of Magnetosomes
at Ambient Temperatures217
6.2.9 Low-temperature (<300 K) Magnetic Properties 218
6.2.10 Magnetosomes and Micromagnetism 220
6.2.11 Magnetosome Magnetization from Electron Holography220
6.3 Mechanism of Bacterial Magnetotaxis. 223
6.3.1 Passive Orientation by the Geomagnetic Field 223
6.3.2 Magneto-aerotaxis 225
6.4 Conclusion. 227
References228

7 Magnetic Ordering due to Dipolar Interaction
in Low Dimensional Materials233
7.1 Introduction 233
7.2 Magnetic Ordering in Pure Dipole Systems 234
7.2.1 The Dipole-Dipole Interaction –
A Well Known Hamiltonian? 234
7.2.2 Ordering Temperature – The Mean-field Approach. 235
7.2.3 Dipolar Ordering in 3D Systems 238
7.2.4 Dipolar Ordering in 2D Systems 243
7.3 Strongly Correlated Extended Objects. 246
7.3.1 Stacking of Magnetic Planes246
7.3.2 3D of 1D – Bunching of Wires or Chains248
7.3.3 2D of 1D – Planar Arrays of Magnetic Wires. 250
7.3.4 2D of 0D – Planar Arrays of Magnetic Dots. 252
7.3.5 1D of 0D – Lines of Magnetic Dots 254
7.4 Weakly Correlated Extended Systems. 255
7.4.1 Low Dimensional Molecular-based Magnets. 255
7.4.2 3D Ordering Due to Dipolar Interaction – A Model261
7.5 Conclusion. 265
References266

8 Spin Transition Phenomena .. 271
8.1 Introduction 271
8.2 Physical Characterization. 272
8.2.1 Occurrence of Thermal Spin Transition272
8.2.2 Magnetic Susceptibility Measurements. 274
8.2.3 Optical Spectroscopy 275
8.2.4 Vibrational Spectroscopy276
8.2.5 57Fe Mossbauer Spectroscopy ̈ 277
8.2.6 Calorimetry279
8.2.7 Diffraction Methods 280
8.2.8 X-ray Absorption Spectroscopy. 281
8.2.9 Positron-annihilation Spectroscopy 282
8.2.10 Nuclear Resonant Scattering of Synchrotron Radiation283
8.2.11 Magnetic Resonance Studies (NMR, EPR)284
8.3 Highlights of Past Research 285
8.3.1 Chemical Influence on Spin-crossover Behavior 285
8.3.2 Structural Insights 289
8.3.3 Influence of Crystal Quality291
8.3.4 Theoretical Approaches to Spin Transition Phenomena292
8.3.5 Influence of a Magnetic Field299
8.3.6 Two-step Spin Transition. 299
8.3.7 LIST Experiments 306
8.3.8 Formation of Correlations During HS → LS relaxation309
8.3.9 Nuclear Decay-induced Spin Crossover313
8.4 New Trends in Spin Crossover Research 320
8.4.1 New Types of Spin Crossover Material320
8.4.2 New Effects and Phenomena326
References334

9 Interpretation and Calculation of Spin-Hamiltonian Parameters
in Transition Metal Complexes345
9.1 Introduction 345
9.2 The Spin-Hamiltonian347
9.2.1 The SH 347
9.2.2 Eigenstates of the SH 348
9.2.3 Matrix Elements of the SH349
9.2.4 Comments. 352
9.3 The Physical Origin of Spin-Hamiltonian Parameters 352
9.3.1 Many-electron Wavefunctions and the Zeroth-order Hamiltonian 352
9.3.2 Perturbing Operators for Magnetic Interactions 355
9.3.3 Theory of Effective Hamiltonians 361
9.3.4 Equations for Spin-Hamiltonian Parameters. 363
9.3.5 Formulation in Terms of Molecular Orbitals. 371
9.4 Ligand Field and Covalency Effects on SH Parameters 380
9.4.1 Molecular Orbitals for Inorganic Complexes. 380
9.4.2 Ligand Field Energies 381
9.4.3 Matrix Elements over Molecular Orbitals385
9.4.4 “Central Field” versus “Symmetry Restricted” Covalency. 392
9.4.5 Ligand-field Theory of Zero-field Splittings395
9.4.6 Ligand-field Theory of the g-Tensor 396
9.4.7 Ligand-field Theory of Hyperfine Couplings. 397
9.4.8 Table of Hyperfine Parameters. 399
9.4.9 Examples of Ligand-field Expressions
for Spin Hamiltonian Parameters 401
9.5 Case Studies of SH Parameters. 414
9.5.1 CuCl2−4 and the Blue Active Site: g and AM Values. 415
9.5.2 FeCl−4 and the Fe(SR)−4 Active Site: Zero-field Splitting (ZFS)420
9.6 Computational Approaches to SH Parameters423
9.6.1 Hartree–Fock Theory 424
9.6.2 Configuration Interaction426
9.6.3 Density Functional Theory427
9.6.4 Coupled-perturbed SCF Theory 428
9.6.5 Relativistic Methods 432
9.6.6 Calculation of Zero-field Splittings 433
9.6.7 Calculation of g-Values. 435
9.6.8 Calculation of Hyperfine Couplings 444
9.7 Concluding Remarks455
9.8 Appendix: Calculation of Spin-Orbit Coupling Matrix Elements456
References458

10 Chemical Reactions in Applied Magnetic Fields .. 467
10.1 Introduction 467
10.2 Gas-phase Reactions467
10.2.1 Gaseous Combustion 467
10.2.2 Carbon Nanotube and Fullerene Synthesis468
10.2.3 Liquid-phase Reactions. 470
10.2.4 Asymmetric Synthesis 470
10.2.5 Electrodeposition . 471
10.3 Solid-phase Reactions472
10.3.1 Self-propagating High-temperature Synthesis (SHS). 472
10.3.2 SHS Reactions in High Fields (1 to 20 T)475
10.3.3 Time-resolved X-ray Diffraction Studies476
10.3.4 Possible Field-dependent Reaction Mechanisms 479
10.4 Conclusions 479
References480

Index483

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