Experimental Techniques in Magnetism and Magnetic Materials

360 Pages·2022·12.217 MB·English

by  S. B. Roy

Experimental Techniques in
Magnetism and Magnetic Materials
The field of magnetism and magnetic materials has diverse applications in
areas including information technology, wireless communication, microelectronics,
information storage, and biotechnology. Thistext discusses experimental techniques
for high-resolution measurements of magnetic properties of materials at both
macroscopic and microscopic levels. It is meant to be a comprehensive introduction
to graduate students and academicians in the fields of physics and materials science
wishing to conduct research in magnetism and magnetic materials.
Starting with a brief history of the subject and insights into its contemporary
applications, the book provides a concise exposition of the phenomenology of
magnetism. It then covers a wide spectrum of experimental methodologies to
study both the microscopic and macroscopic aspects of various kinds of magnetic
phenomenaand materials. Thephysical principles behindeach kind of experimental
technique with a broad-based introduction to instrumentation are also presented.
The main text is augmented by appendices on the generation of the magnetic field,
units in magnetism, and demagnetization fields.
Sindhunil Barman Roy is Emeritus Professor and Raja Ramanna Fellow at the
UGC-DAE Consortium for Scientific Research, Indore, India. His research includes
experimental and theoretical aspects of magnetism and superconductivity. He has
publishedmorethan200researchpapersininternationalpeer-reviewedjournalsand
holds two US patents.

Experimental Techniques in
Magnetism and Magnetic
Materials
Sindhunil Barman Roy
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(cid:2)c SindhunilBarmanRoy2022
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Firstpublished2022
PrintedinIndia
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ISBN978-1-108-48998-0 Hardback
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To all my teachers, the first of the lot being my late parents

Contents
Preface xiii
I Introduction to Magnetism and Magnetic Materials 1
1 A Short History of Magnetism and Magnetic Materials 3
2 Role of Magnetism and Magnetic Materials in Modern Society 13
II Basic Phenomenology of Magnetism 19
3 Magnetic Moment and the Effect of Crystal Environment 23
3.1 Magnetic Moment and Magnetization . . . . . . . . . . . . . . . . 23
3.1.1 Magnetic Moment . . . . . . . . . . . . . . . . . . . . . . . 23
3.1.2 Magnetization . . . . . . . . . . . . . . . . . . . . . . . . . 25
3.2 Classical Electromagnetism, Magnetic Moment, and Angular
Momentum . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 26
3.3 Precession of Magnetic Moment . . . . . . . . . . . . . . . . . . . 30
3.4 Magnetization, Magnetic Field, and Magnetic Susceptibility . . . 31
3.5 Orbital and Spin Angular Momentum of Electron and Magnetic
Moment . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 32
3.6 Magnetism of Isolated Atoms and Ions . . . . . . . . . . . . . . . 33
3.7 Diamagnetism . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 34
viii Contents
3.8 Paramagnetism . . . . . . . . . . . . . . . . . . . . . . . . . . . . 37
3.8.1 Classical theory of paramagnetism . . . . . . . . . . . . . . 37
3.8.2 Quantum theory of paramagnetism . . . . . . . . . . . . . . 40
3.8.3 van Vleck paramagnetism . . . . . . . . . . . . . . . . . . . 41
3.9 Ground State of Ions and Hund’s Rules . . . . . . . . . . . . . . . 42
3.9.1 Fine structure . . . . . . . . . . . . . . . . . . . . . . . . . 42
3.9.2 Hund’s rules . . . . . . . . . . . . . . . . . . . . . . . . . . 43
3.9.3 Russel–Saunders coupling versus(cid:2)j–(cid:2)j coupling . . . . . . . . 43
3.10 Effect of Crystal Environment on Magnetic Ions . . . . . . . . . . 44
3.10.1 Crystal fields and their origin . . . . . . . . . . . . . . . . . 44
3.10.2 Quenching of orbitals . . . . . . . . . . . . . . . . . . . . . 47
3.10.3 Jahn–Teller effect . . . . . . . . . . . . . . . . . . . . . . . . 48
4 Exchange Interactions and Magnetism in Solids 49
4.1 Coupling between Spins . . . . . . . . . . . . . . . . . . . . . . . . 49
4.2 Origin of Exchange Interactions . . . . . . . . . . . . . . . . . . . 51
4.3 Physical Meaning of Exchange Energy . . . . . . . . . . . . . . . . 54
4.4 Direct Exchange . . . . . . . . . . . . . . . . . . . . . . . . . . . . 55
4.5 Indirect Exchange in Insulating Solids . . . . . . . . . . . . . . . . 55
4.5.1 Superexchange . . . . . . . . . . . . . . . . . . . . . . . . . 55
4.5.2 Double exchange . . . . . . . . . . . . . . . . . . . . . . . . 59
4.5.3 Anisotropic exchange interaction: Dzyaloshinski–Moriya
interaction . . . . . . . . . . . . . . . . . . . . . . . . . . . 61
4.6 Indirect Exchange in Metals . . . . . . . . . . . . . . . . . . . . . 62
5 Magnetically Ordered States in Solids 63
5.1 Ferromagnetism . . . . . . . . . . . . . . . . . . . . . . . . . . . . 63
5.1.1 Magnetic susceptibility in a ferromagnet . . . . . . . . . . . 67
5.2 Antiferromagnetism . . . . . . . . . . . . . . . . . . . . . . . . . . 68
5.2.1 Magnetic susceptibility in an antiferromagnet . . . . . . . . 69
5.3 Ferrimagnetism . . . . . . . . . . . . . . . . . . . . . . . . . . . . 71
5.4 Helical Magnetic Order . . . . . . . . . . . . . . . . . . . . . . . . 71
5.5 Spin-Glass Order. . . . . . . . . . . . . . . . . . . . . . . . . . . . 72
5.6 Spin Waves in Ferromagnets . . . . . . . . . . . . . . . . . . . . . 74
5.7 Domains and Domain Wall . . . . . . . . . . . . . . . . . . . . . . 79
5.8 Magnetic Skyrmion . . . . . . . . . . . . . . . . . . . . . . . . . . 82
5.9 Magnetic Anisotropy . . . . . . . . . . . . . . . . . . . . . . . . . 83
5.10 Magnetization Process in Ferromagnets . . . . . . . . . . . . . . . 85