Acknowledgments .............................................. xiii
I. Basics
1 Review of basic magnetostatics ............................. 3
1.1 Magnetic field ............................................. 4
1.1.1 Magnetic poles ...................................... 4
1.1.2 Magnetic flux ....................................... 6
1.1.3 Circulating currents ................................ 6
1.1.4 Ampere's circuital law .............................. 7
1.1.5 Biot-Savart law ..................................... 8
1.1.6 Field from a straight wire .......................... 8
1.2 Magnetic moment ........................................... 10
1.2.1 Magnetic dipole .................................... 11
1.3 Definitions ............................................... 11
Homework .................................................. 12
2 Magnetization and magnetic materials ...................... 14
2.1 Magnetic induction and magnetization ...................... 14
2.2 Flux density .............................................. 15
2.3 Susceptibility and permeability ........................... 16
2.4 Hysteresis loops .......................................... 18
2.5 Definitions ............................................... 19
2.6 Units and conversions ..................................... 19
Homework .................................................. 20
3 Atomic origins of magnetism ............................... 22
3.1 Solution of the Schrödinger equation for a free atom ...... 22
3.1.1 What do the quantum numbers represent? ............. 25
3.2 The normal Zeeman effect .................................. 27
3.3 Electron spin ............................................. 30
3.4 Extension to many-electron atoms .......................... 31
3.4.1 Pauli exclusion principle .......................... 32
3.5 Spin-orbit coupling ....................................... 32
3.5.1 Russell-Saunders coupling .......................... 32
3.5.2 Hund's rules ....................................... 34
3.5.3 jj coupling ........................................ 35
3.5.4 The anomalous Zeeman effect ........................ 35
Homework .................................................. 37
4 Diamagnetism .............................................. 38
4.1 Observing the diamagnetic effect .......................... 38
4.2 Diamagnetic susceptibility ................................ 39
4.3 Diamagnetic substances .................................... 41
4.4 Uses of diamagnetic materials ............................. 42
4.5 Superconductivity ......................................... 42
4.5.1 The Meissner effect ................................ 43
4.5.2 Critical field ..................................... 44
4.5.3 Classification of superconductors .................. 44
4.5.4 Superconducting materials .......................... 44
4.5.5 Applications for superconductors ................... 46
Homework .................................................. 46
5 Paramagnetism ............................................. 48
5.1 Langevin theory of paramagnetism .......................... 49
5.2 The Curie-Weiss law ....................................... 52
5.3 Quenching of orbital angular momentum ..................... 54
5.4 Pauli paramagnetism ....................................... 55
5.4.1 Energy bands in solids ............................. 56
5.4.2 Free-electron theory of metals ..................... 58
5.4.3 Susceptibility of Pauli paramagnets ................ 60
5.5 Paramagnetic oxygen ....................................... 62
5.6 Uses of paramagnets ....................................... 63
Homework .................................................. 64
6 Interactions in ferromagnetic materials ................... 65
6.1 Weiss molecular field theory .............................. 66
6.1.1 Spontaneous magnetization .......................... 66
6.1.2 Effect of temperature on magnetization ............. 67
6.2 Origin of the Weiss molecular field ....................... 69
6.2.1 Quantum mechanics of the He atom .................. 70
6.3 Collective-electron theory of ferromagnetism .............. 73
6.3.1 The Slater-Pauling curve .......................... 76
6.4 Summary ................................................... 76
Homework .................................................. 78
7 Ferromagnetic domains ..................................... 79
7.1 Observing domains ......................................... 79
7.2 Why domains occur ......................................... 81
7.2.1 Magnetostatic energy ............................... 81
7.2.2 Magnetocrystalline energy .......................... 82
7.2.3 Magnetostrictive energy ............................ 84
7.3 Domain walls .............................................. 85
7.4 Magnetization and hysteresis .............................. 87
Homework .................................................. 92
8 Antiferromagnetism ........................................ 96
8.1 Neutron diffraction ....................................... 97
8.2 Weiss theory of antiferromagnetism ....................... 101
8.2.1 Susceptibility above TN ........................... 102
8.2.2 Weiss theory at TN ................................ 103
8.2.3 Spontaneous magnetization below TN ................ 103
8.2.4 Susceptibility below TN ........................... 103
8.3 What causes the negative molecular field? ................ 107
8.4 Uses of antiferromagnets ................................. 110
Homework ................................................. 112
9 Ferrimagnetism ........................................... 113
9.1 Weiss theory of ferrimagnetism ........................... 114
9.1.1 Weiss theory above TC ............................. 115
9.1.2 Weiss theory below TC ............................. 117
9.2 Ferrites ................................................. 120
9.2.1 The cubic ferrites ................................ 120
9.2.2 The hexagonal ferrites ............................ 124
9.3 The garnets .............................................. 125
9.4 Half-metallic antiferromagnets ........................... 126
Homework ................................................. 127
10 Summary of basics ........................................ 130
10.1 Review of types of magnetic ordering ..................... 130
10.2 Review of physics determining types of magnetic
ordering ............................................ 131
II. Magnetic phenomena
11 Anisotropy ............................................... 135
11.1 Magnetocrystalline anisotropy ............................ 135
11.1.1 Origin of magnetocrystalline anisotropy ........... 136
11.1.2 Symmetry of magnetocrystalline anisotropy ......... 138
11.2 Shape anisotropy ......................................... 139
11.2.1 Demagnetizing field ............................... 139
11.3 Induced magnetic anisotropy .............................. 141
11.3.1 Magnetic annealing ................................ 141
11.3.2 Roll anisotropy ................................... 142
11.3.3 Explanation for induced magnetic anisotropy ....... 142
11.3.4 Other ways of inducing magnetic anisotropy ........ 143
Homework ................................................. 144
12 Nanoparticles and thin films ............................. 145
12.1 Magnetic properties of small particles ................... 145
12.1.1 Experimental evidence for single-domain
particles ......................................... 147
12.1.2 Magnetization mechanism ........................... 147
12.1.3 Superparamagnetism ................................ 148
12.2 Thin-film magnetism ...................................... 152
12.2.1 Structure ......................................... 152
12.2.2 Interfaces ........................................ 153
12.2.3 Anisotropy ........................................ 153
12.2.4 How thin is thin? ................................. 154
12.2.5 The limit of two-dimensionality ................... 154
13 Magnetoresistance ........................................ 156
13.1 Magnetoresistance in normal metals ....................... 157
13.2 Magnetoresistance in ferromagnetic metals ................ 158
13.2.1 Anisotropic magnetoresistance ..................... 158
13.2.2 Magnetoresistance from spontaneous magnetization .. 159
13.2.3 Giant magnetoresistance ........................... 160
13.3 Colossal magnetoresistance ............................... 164
13.3.1 Superexchange and double exchange ................. 164
Homework ................................................. 168
14 Exchange bias ............................................ 169
14.1 Problems with the simple cartoon mechanism ............... 171
14.1.1 Ongoing research on exchange bias ................. 172
14.2 Exchange anisotropy in technology ........................ 173
III. Device applications and novel materials
15 Magnetic data storage .................................... 177
15.1 Introduction ............................................. 177
15.2 Magnetic media ........................................... 181
15.2.1 Materials used in magnetic media .................. 181
15.2.2 The other components of magnetic hard disks ....... 183
15.3 Write heads .............................................. 183
15.4 Read heads ............................................... 185
15.5 Future of magnetic data storage .......................... 186
16 Magneto-optics and magneto-optic recording ............... 189
16.1 Magneto-optics basics .................................... 189
16.1.1 Kerr effect ....................................... 189
16.1.2 Faraday effect .................................... 191
16.1.3 Physical origin of magneto-optic effects .......... 191
16.2 Magneto-optic recording .................................. 193
16.2.1 Other types of optical storage, and the future
of magneto-optic recording ........................ 196
17 Magnetic semiconductors and insulators ................... 197
17.1 Exchange interactions in magnetic semiconductors
and insulators ........................................... 198
17.1.1 Direct exchange and superexchange ................. 199
17.1.2 Carrier-mediated exchange ......................... 199
17.1.3 Bound magnetic polarons ........................... 200
17.2 II-VI diluted magnetic semiconductors - (Zn,Mn)Se ........ 201
17.2.1 Enhanced Zeeman splitting ......................... 201
17.2.2 Persistent spin coherence ......................... 202
17.2.3 Spin-polarized transport .......................... 203
17.2.4 Other architectures ............................... 204
17.3 III-V diluted magnetic semiconductors - (Ga,Mn)As ........ 204
17.3.1 Rare-earth-group-V compounds - ErAs ............... 207
17.4 Oxide-based diluted magnetic semiconductors .............. 208
17.5 Ferromagnetic insulators ................................. 210
17.5.1 Crystal-field and Jahn-Teller effects ............. 210
17.5.2 YTi03 and SeCuO3 .................................. 211
17.5.3 BiMnOj ............................................ 213
17.5.4 Europium oxide .................................... 214
17.5.5 Double perovskites ................................ 215
17.6 Summary .................................................. 215
18 Multiferroics ............................................ 216
18.1 Comparison of ferromagnetism and other types of ferroic
ordering ................................................. 216
18.1.1 Ferroelectrics .................................... 216
18.1.2 Ferroelastics ..................................... 219
18.1.3 Ferrotoroidics .................................... 220
18.2 Multiferroics that combine magnetism and
ferroelectricity ......................................... 221
18.2.1 The contra-indication between magnetism and
ferroelectricity .................................. 222
18.2.2 Routes to combining magnetism and
ferroelectricity .................................. 223
18.2.3 The magnetoelectric effect ........................ 225
18.3 Summary .................................................. 228
Epilogue ...................................................... 229
Solutions to selected exercises ............................... 230
References .................................................... 262
Index ......................................................... 270
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