The Physics of Ferromagnetism

Transcription

1 Terunobu Miyazaki Hanmin Jin The Physics of Ferromagnetism Springer

2 Contents Part I Foundation of Magnetism 1 Basis of Magnetism Basic Magnetic Laws and Magnetic Quantities Basic Laws of Magnetic Forces, Magnetic Induction Vector, and Magnetic Moment Vectors of Magnetization, Magnetic polarization and Magnetic field, and Magnetic Polarization Moment Maxwell Equations Magnetic Vector Potential Magnetic Moment Magnetic Moment of Current Coil Magnetic Moment of Electron Spin Magnetic Field Strength, Magnetic Induction, Magnetization, Permeability, and Susceptibility Magnetic Coulomb's law, Static Magnetic Field, and Magnetic Circuit Magnetic Charge and Magnetic Coulomb's Law Examples of Application of Magnetic Coulomb's Law Magnetic Field Produced by Electric Current Volume Integral of Scalar Products of rin, with lt ä,, and B Magnetic Circuit Zeeman Energy, Magnetization Energy, and Magnetostatic Energy Zeeman Energy Magnetization Energy Magnetostatic Energy 19 vii

3 viii Contents 1.4 Thermodynamics for Magnetic Media Principles of Thermodynamics for Magnetic Media Free Energy and Thermal Potential Stabilization Conditions for a System at Constant Temperature First- and Second-Order Transformations Magneto-Caloric Effect Hamiltonian of an Electric Charged Particle in Static Electric and Magnetic Fields Hamiltonian and Momentum in Classical Mechanics Hamiltonian and Momentum in Quantum Mechanics 28 Appendix 1: Physical Constants 29 Appendix 2: Units and Their Conversions 29 Appendix 3: Selections From Vector Analysis 30 References 33 2 Magnetism of Atoms Electron Configuration of Atom Electron Spin Hartree Fock Equations Central Field Approximation Electron Configuration of Atom Angular Momentum Operators Term and Multiplet Residual Coulomb Interaction and Term Spin-Orbit Interaction and Multiplet Intrinsic Magnetic Moment and Gyromagnetic Ratio of Atom Magnetic Moment and Gyromagnetic Ratio of an Electron Orbit Magnetic Moment and Gyromagnetic Ratio of an Electron Spin Intrinsic Magnetic Moment, g Factor, and Effective Magnetic Moment of an Atom Paramagnetism and Diamagnetism of Atom Magnetic Moment Operator of an Atom in a Magnetic Field Paramagnetism of Atom Diamagnetism of Atom 59

4 Contents ix 2.5 Exchange Interaction in He Atom Exchange Hamiltonian Positiveness of Exchange Integral of Form (2.157) Exchange Interaction in H2 Molecule Eigenstates and Eigenenergies of the Two Electron System of H Exchange Interaction in H Hyperfine Interactions in Atom Spin, Magnetic Moment, and Quadrupole of Nucleus Hyperfine Interactions Hyperfine Magnetic Interaction Electric-Quadrupole Interaction Hyperfine Coulomb Interaction of the Nucleus with an Overlapping Electron Cloud Total Hyperfine Interaction 73 Appendix 4: Selections From Group Theory 75 Appendix 5: Second Quantized Representation of Operators 87 Appendix 6: Perturbation Theory 94 Reference s 96 3 Magnetism of Solids Classification of Magnetic Properties Diamagnetism Paramagnetism Antiferromagnetism Ferromagnetism Ferrimagnetism Magnetic Glass Spin Glass Magnetic Moment of Atom (Ion) in Solids Fe-Ni Alloy Magnetic Moment of 3d Atom in Alloys Magnetic Moment of 3d Ion in Oxides Magnetic Moment of 4f Ion in Solids Neutron Diffraction and Magnetic Structure Neutron Diffraction Magnetic Structure of MnO Magnetic Structure of Ho Metal Magnetic Structures of Spinel Ferrites Magnetic Structure of Ba(Sr) Ferrites Magnetic Structures of Rare Earth hon Gamets Magnetic Structures of Perovskite Ferrites Magnetic Structure of Fe Metal 116

5 x Contents 3.4 Molecular Field Theory Weiss's Molecular Field Theory N6el's Molecular Field Theory Origin of Molecular Field Spin Wave Spin Wave Quasiclassical Picture of Spin Wave Bloch T3 / 2 Law Crystalline Electric Field CEF Interactions of 3d and 4f Electrons CEF Hamiltonian CEF Effects for 3d Ion at the B Site of Spinel Ferrite Jahn Teller Effect Quenching of Orbital Angular Momentum Gyromagnetic Effect Precession Motion of Magnetization Vector in a Magnetic Field Free Electron Gas Eigenstate and Eigenenergy of Free Electron Energy Band of Free Electron Gas Magnetic Properties of Free Electrons Essentials of Band Theory Introduction Bloch Wave Band Theory Based an the Mean Field Approximation Stoner Model of Ferromagnetism Density Functional Theory Local Density Approximation and Generalized Gradient Approximation Methods of Energy Band Calculations Examples of Band Structures Hyperfine Interactions in Solids Hamiltonian of a Nucleus in a Magnetic Field Hyperfine Energy Eigenvalue Hyperfine Magnetic Field Principle of NMR Spectroscopy Principle of Mössbauer Spectroscopy Examples of NMR and Mössbauer Spectroscopy Application 169 References 173

6 Contents xi 4 Exchange Interaction Direct Exchange Interaction in Solid Hamiltonian of One Magnetic Electron Atom System Exchange Hamiltonian in H Exchange Hamiltonian in fil Total Exchange Hamiltonian Interatomic Exchange Hamiltonian in Multi Magnetic Electron Atom System Exchange Integral as a Function of Distance Between a Pair of Atoms Superexchange Interaction Physical Picture of Superexchange Interaction Semi-Quantitative Analysis of Superexchange Interaction Anderson's Potential and Kinetic Exchanges RKKY Exchange Interaction f-s Exchange Hamiltonian Hex First-Order Perturbation of t Oscillatory Decay of Conduction Electron Magnetization Indirect Exchange Interaction Between Rare-Earth Ions Curie Temperature and de Gennes Factor Double Exchange Interaction Classic Expressions of Exchange Energy Exchange Energy in Cubic Crystals Exchange Energy in Non-Cubic Crystals 203 Reference s Magnetic Anisotropy Magnetocrystalline Anisotropy Anisotropy of Magnetization Curve of Crystal and Concept of Magnetocrystalline Anisotropy Phenomenological Expressions of FK Magnetic Anisotropy Field Mechanisms of Magnetocrystalline Anisotropy Magnetic Moment Interaction Model Single-Ion Model Single-Ion Model for 3d Ion Single-Ion Model for 4f Ion Two-Ion Model 223

7 xii Contents 5.3 Shape Anisotropy Demagnetizing Field and Demagnetizing Energy Demagnetizing Factor and Demagnetizing Energy of an Ellipsoidal Magnet and Shape Anisotropy Induced Magnetic Anisotropy Anisotropy of Co Metal Induced by Cooling in a Magnetic Field Atomic Pair Ordering Anisotropy Shape Anisotropy of Magnetic Film Deposited by Oblique Incidence Magnetization-Induced Anisotropy of Thin Film Magnetic Anisotropy of Alnico Induced by Tempering in a Magnetic Field Unidirectional Anisotropy of Co-CoO Particles Induced by Cooling in a Magnetic Field Magnetic Anisotropy of Amorphous Gd-Co Thin Film Easy Axis Normal to the Film Plane Magnetic Field-Induced Anisotropy of Cu-2%Mn Spin-Glass Random Anisotropy and Effective Anisotropy Random Anisotropy of Amorphous Magnetic Materials Effective Anisotropy of Amorphous Magnetic Materials Effective Anisotropy of Nanocrystalline Materials 242 References Magnetostrictive Effects Magnetostriction and Magneto-Elastic Energy Magnetostriction Phenomena Elastic Mechanics for Cubic Crystal Magneto-Elastic Energy Spontaneous Strain Tensor Phenomenological Expression of Magnetostriction for Cubic Crystal Phenomenological Expressions of Magnetostriction for Hexagonal Crystal Origin of Magnetostriction Stress Energy 255 References 259

8 Contents xiii 7 Magnetic Domain 7.1 Magnetostatic Energies of Strip and Chessboard Domain Structures 7.2 Magnetic Domain Wall Bloch Wall General Expressions of the Structure and Energy of Bloch Wall Wall of Easy Axis Crystal Wall of Cubic Crystal Wall of Cubic Crystal Under Stress Typical Values of.5,, and y w N6e1 Wall Magnetic Domain Structure Methods of Domain Observation Analyses of Domain Structures of Easy Axis Crystal Plate Domain Structures of Easy Axis Crystal Plates Observed in Experiment Measurement of 3), and A Values Magnetic Bubble Domains in Cubic Crystal Plate Domains Observed in Polycrystals Single Domain M, Distribution in Submicron-Scale Dots Superparamagneti sm 285 References Micromagnetism Brown's Equation Brown's Equation Nucleation of Magnetization Reversal in Infinite Long Cylindrical Crystal Finite Element Method Domain Wall in Bulk Nd2 Feiß Models of Nanocrystalline NdFeB Effects of H Direction and the Value of N an the Calculation of Hysteresis Curve of Nanocrystalline NdFeB Hysteresis Curve of Nanocrystalline NdFeB 298 References 301

9 xiv Contents Part II Magnetic Materials 9 Soft Magnetism Magnetization Process Rotation Magnetization Asteroid Curve Magnetic Domain Wall Displacement AC Magnetization and Loss Soft Magnetic Material Brief Outline Details of Development Research of Magnetic Metallic Soft Material 319 References Hard Magnetism Requirements an Permanent Magnetic Properties Coercivity Mechanisms Coercivity of Rotation Process Characteristics of Coercivity Dominated by Nucleation of Reversed Domain Characteristics of Coercivity Dominated by Domain Wall Pinning Coercivity of Domain Wall Pinning at Planar Defect Permanent Magnetic Materials Survey of Permanent Magnets References and Their Properties Ba(Sr) Ferrites Alnico FeCrCo PtCo Foundation of Rare Earth Magnets SmCo5 SmCoCuFeZr NdFeB Interstitial Sm 2Fe 17N, and NdFe10.5M015 1\ix Bond Magnets Part III Spintronics 11 Magnetoresistance Effect History of research 373

10 Contents xv 11.2 Basis of Electrical Conduction Drift Velocity and Fermi Velocity Matthiessen' s Law Two-Current Model Resistance Due to Spin Flip Temperature Dependence of p How to Obtain pl,p 1, and ce = pilpt Classification of Magnetoresistance Effects Anisotropic Magnetoresistance Effect Origin of Anisotropic Magnetoresistance Effect Magnetoresistance Curve Based an the Magnetization Rotation Model Giant Magnetoresistance Effect of Metallic Superlattices and Multilayer Films 393 References Tunnel Magnetoresistance Effect Introduction Root of Tunnel Effect Root of Magnetoresistance Effect Principle of TMR Barrier Height Dependence of TMR Ratio Comparison Among TMR, AMR, and PHE Effects Spin Valve-Type Junction with Exchange Bias Layer Single Crystalline High-Quality Tunnel Junction Tunnel Junction with MgO Barrier Tunnel Junction with Half Metal Electrodes Crystal Structure Magnetic Moment, Curie Temperature, and Magnetic Anisotropy Magnetoresistance Other Tunnel Junctions Giant Magnetoresistance Effect in Granular Structure Tunnel Magnetoresistance of Magnetic Semiconductors Organic Molecules-Ferromagnet Hybrid Tunnel Junction 429 References MRAM Introduction History of Magnetic Memory Principles 435

11 xvi Contents 13.4 Spin Transfer Torques and the Change of Cell Structure Spin Transfer Torque From In-Plane Magnetization to Out of Plane Magnetization Issues of MRAM Development High Signal Power Output High Speed Writing/Reading Low Power Consumption High Reliabilities Making to Large Capacities 444 References Technology that Accompanies the Development of Spintronics Devices Analysis of the / V Curve Inelastic Electron Tunneling Spectroscopy Conducting Atomic Force Microscope and STM Measurement of Polarization Spin Dynamics LLG Equation and Gilbert Damping Experiment Spin Pumping Damping Constant of Various Kinds of Materials References 475 Index 477