Contents. Acknowledgments

Transcription

1 MAGNETIC MATERIALS Fundamentals and Applications Second edition NICOLA A. SPALDIN University of California, Santa Barbara CAMBRIDGE UNIVERSITY PRESS

2 Contents Acknowledgments page xiii I Basics 1 Review of basic magnetostatics Magnetic field Magnetic poles Magnetic flux Circulating currents Ampre's circuital law Biot Savart law Field from a straight wire Magnetic moment Magnetic dipole Definitions 11 Homework 12 2 Magnetization and magnetic materials Magnetic induction and magnetization Flux density Susceptibility and permeability Hysteresis loops Definitions Units and conversions 19 Homework 20 3 Atomic origins of magnetism Solution of the Schrödinger equation for a free atom What do the quantum numbers represent? The normal Zeeman effect 27 vii

3 viii Contents 3.3 Electron spin Extension to many-electron atoms Pauli exclusion principle Spin orbit coupling Russell Saunders coupling Hund's rules jj coupling The anomalous Zeeman effect 35 Homework 37 4 Diamagnetism Observing the diamagnetic effect Diamagnetic susceptibility Diamagnetic substances Uses of diamagnetic materials Superconductivity The Meissner effect Critical field Classification of superconductors Superconducting materials Applications for superconductors 46 Homework 46 5 Paramagnetism Langevin theory of paramagnetism The Curie Weiss law Quenching of orbital angular momentum Pauli paramagnetism Energy bands in solids Free-electron theory of metals Susceptibility of Pauli paramagnets Paramagnetic oxygen Uses of paramagnets 63 Homework 64 6 Interactions in ferromagnetic materials Weiss molecular field theory Spontaneous magnetization Effect of temperature an magnetization Origin of the Weiss molecular field Quantum mechanics of the He atom Collective-electron theory of ferromagnetism The Slater Pauling curve 76

4 Contents 6.4 Summary 76 Homework 78 7 Ferromagnetic domains Observing domains Why domains occur Magnetostatic energy Magnetocrystalline energy Magnetostrictive energy Domain walls Magnetization and hysteresis 87 Homework 92 8 Antiferromagnetism Neutron diffraction Weiss theory of antiferromagnetism Susceptibility above TN Weiss theory at TN Spontaneous magnetization below TN Susceptibility below TN What causes the negative molecular field? Uses of antiferromagnets 110 Homework Ferrimagnetism Weiss theory of ferrimagnetism Weiss theory above Tc Weiss theory below Tc Ferrites The cubic ferrites The hexagonal ferrites The gamets Half-metallic antiferromagnets 126 Homework Summary of basics Review of types of magnetic ordering Review of physics determining types of magnetic ordering 131 II Magnetic phenomena 11 Anisotropy Magnetocrystalline anisotropy Origin of magnetocrystalline anisotropy Symmetry of magnetocrystalline anisotropy 138 ix

5 x Contents 11.2 Shape anisotropy Demagnetizing field Induced magnetic anisotropy Magnetic annealing Roll anisotropy Explanation for induced magnetic anisotropy Other ways of inducing magnetic anisotropy 143 Homework Nanoparticles and thin films Magnetic properties of small particles Experimental evidence for single-domain particles Magnetization mechanism Superparamagnetism Thin-film magnetism Structure Interfaces Anisotropy How thin is thin? The limit of two-dimensionality Magnetoresistance Magnetoresistance in normal metals Magnetoresistance in ferromagnetic metals Anisotropic magnetoresistance Magnetoresistance from spontaneous magnetization Giant magnetoresistance Colossal magnetoresistance Superexchange and double exchange 164 Homework Exchange bias Problems with the simple cartoon mechanism Ongoing research an exchange bias Exchange anisotropy in technology 173 III Device applications and novel materials 15 Magnetic data storage Introduction Magnetic media Materials used in magnetic media The other components of magnetic hard disks Write heads 183

6 Contents 15.4 Read heads Future of magnetic data storage Magneto-optics and magneto-optic recording Magneto-optics basics Kerr effect Faraday effect Physical origin of magneto-optic effects Magneto-optic recording Other types of optical storage, and the future of magneto-optic recording Magnetic semiconductors and insulators Exchange interactions in magnetic semiconductors and insulators Direct exchange and superexchange Carrier-mediated exchange Bound magnetic polarons II VI diluted magnetic semiconductors (Zn,Mn)Se Enhanced Zeeman splitting Persistent spin coherence Spin-polarized transport Other architectures III V diluted magnetic semiconductors (Ga,Mn)As Rare-earth group-v compounds ErAs Oxide-based diluted magnetic semiconductors Ferromagnetic insulators Crystal-field and Jahn Teller effects YTiO3 and SeCu BiMnO Europium oxide Double perovskites Summary Multiferroics Comparison of ferromagnetism and other types of ferroic ordering Ferroelectrics Ferroelastics Ferrotoroidics Multiferroics that combine magnetism and ferroelectricity The contra-indication between magnetism and ferroelectricity 222 xi

7 xii Contents Routes to combining magnetism and ferroelectricity The magnetoelectric effect Summary 228 Epilogue 229 Solutions to selected exercises 230 References 262 Index 270