Introduction to Magnetic Materials E-Book

B. D. Cullity

• Herausgeber: John Wiley & Sons
• Kategorie: Fachliteratur
• Sprache: Englisch

Seitenzahl: 992

Veröffentlichungsjahr: 2011

Beschreibung

Introduction to Magnetic Materials, 2nd Edition covers the basics of magnetic quantities, magnetic devices, and materials used in practice. While retaining much of the original, this revision now covers SQUID and alternating gradient magnetometers, magnetic force microscope, Kerr effect, amorphous alloys, rare-earth magnets, SI Units alongside cgs units, and other up-to-date topics. In addition, the authors have added an entirely new chapter on information materials. The text presents materials at the practical rather than theoretical level, allowing for a physical, quantitative, measurement-based understanding of magnetism among readers, be they professional engineers or graduate-level students.

Leseprobe

CONTENTS

PREFACE TO THE FIRST EDITION

PREFACE TO THE SECOND EDITION

1 DEFINITIONS AND UNITS

1.1 Introduction

1.2 The cgs-emu System of Units

1.3 Magnetic Moment

1.4 Intensity of Magnetization

1.5 Magnetic Dipoles

1.6 Magnetic Effects of Currents

1.7 Magnetic Materials

1.8 SI Units

1.9 Magnetization Curves and Hysteresis Loops

2 EXPERIMENTAL METHODS

2.1 Introduction

2.2 Field Production By Solenoids

2.3 Field Production by Electromagnets

2.4 Field Production by Permanent Magnets

2.5 Measurement of Field Strength

2.6 Magnetic Measurements in Closed Circuits

2.7 Demagnetizing Fields

2.8 Magnetic Shielding

2.9 Demagnetizing Factors

2.10 Magnetic Measurements in Open Circuits

2.11 Instruments for Measuring Magnetization

2.12 Magnetic Circuits and Permeameters

2.13 Susceptibility Measurements

Problems

3 DIAMAGNETISM AND PARAMAGNETISM

3.1 Introduction

3.2 Magnetic Moments of Electrons

3.3 Magnetic Moments of Atoms

3.4 Theory of Diamagnetism

3.5 Diamagnetic Substances

3.6 Classical Theory of Paramagnetism

3.7 Quantum Theory of Paramagnetism

3.8 Paramagnetic Substances

4 FERROMAGNETISM

4.1 Introduction

4.2 Molecular Field Theory

4.3 Exchange Forces

4.4 Band Theory

4.5 Ferromagnetic Alloys

4.6 Thermal Effects

4.7 Theories of Ferromagnetism

4.8 Magnetic Analysis Problems

5 ANTIFERROMAGNETISM

5.1 Introduction

5.2 Molecular Field Theory

5.3 Neutron Diffraction

5.4 Rare Earths

5.5 Antiferromagnetic Alloys Problems

6 FERRIMAGNETISM

6.1 Introduction

6.2 Structure of Cubic Ferrites

6.3 Saturation Magnetization

6.4 Molecular Field Theory

6.5 Hexagonal Ferrites

6.6 Other Ferrimagnetic Substances

6.7 Summary: Kinds of Magnetism Problems

7 MAGNETIC ANISOTROPY

7.1 Introduction

7.2 Anisotropy in Cubic Crystals

7.3 Anisotropy in Hexagonal Crystals

7.4 Physical Origin of Crystal Anisotropy

7.5 Anisotropy Measurement

7.6 Anisotropy Measurement (from Magnetization Curves)

7.7 Anisotropy Constants

7.8 Polycrystalline Materials

7.9 Anisotropy in Antiferromagnetics

7.10 Shape Anisotropy

7.11 Mixed Anisotropies Problems

8 MAGNETOSTRICTION AND THE EFFECTS OF STRESS

8.1 Introduction

8.2 Magnetostriction of Single Crystals

8.3 Magnetostriction of Polycrystals

8.4 Physical Origin of Magnetostriction

8.5 Effect of Stress on Magnetic Properties

8.6 Effect of Stress on Magnetostriction

8.7 Applications of Magnetostriction

8.8 ΔE Effect

8.9 Magnetoresistance Problems

9 DOMAINS AND THE MAGNETIZATION PROCESS

9.1 Introduction

9.2 Domain Wall Structure

9.3 Domain Wall Observation

9.4 Magnetostatic Energy and Domain Structure

9.5 Single-Domain Particles

9.6 Micromagnetics

9.7 Domain Wall Motion

9.8 Hindrances to Wall Motion (Inclusions)

9.9 Residual Stress

9.10 Hindrances to Wall Motion (Microstress)

9.11 Hindrances to Wall Motion (General)

9.12 Magnetization by Rotation

9.13 Magnetization in Low Fields

9.14 Magnetization in High Fields

9.15 Shapes of Hysteresis Loops

9.16 Effect of Plastic Deformation (Cold Work) Problems

10 INDUCED MAGNETIC ANISOTROPY

10.1 Introduction

10.2 Magnetic Annealing (Substitutional Solid Solutions)

10.3 Magnetic Annealing (Interstitial Solid Solutions)

10.4 Stress Annealing

10.5 Plastic Deformation (Alloys)

10.6 Plastic Deformation (Pure Metals)

10.7 Magnetic Irradiation

10.8 Summary of Anisotropies

11 FINE PARTICLES AND THIN FILMS

11.1 Introduction

11.2 Single-Domain vs Multi-Domain Behavior

11.3 Coercivity of Fine Particles

11.4 Magnetization Reversal by Spin Rotation

11.5 Magnetization Reversal by Wall Motion

11.6 Superparamagnetism in Fine Particles

11.7 Superparamagnetism in Alloys

11.8 Exchange Anisotropy

11.9 Preparation and Structure of Thin Films

11.10 Induced Anisotropy in Films

11.11 Domain Walls in Films

11.12 Domains in Films Problems

12 MAGNETIZATION DYNAMICS

12.1 Introduction

12.2 Eddy Currents

12.3 Domain Wall Velocity

12.4 Switching in Thin Films

12.5 Time Effects

12.6 Magnetic Damping

12.7 Magnetic Resonance

13 Soft Magnetic Materials

13.1 Introduction

13.2 Eddy Currents

13.3 Losses in Electrical Machines

13.4 Electrical Steel

13.5 Special Alloys

13.6 Soft Ferrites Problems

14 HARD MAGNETIC MATERIALS

14.1 Introduction

14.2 Operation of Permanent Magnets

14.3 Magnet Steels

14.4 Alnico

14.5 Barium and Strontium Ferrite

14.6 Rare Earth Magnets

14.7 Exchange-Spring Magnets

14.8 Nitride Magnets

14.9 Ductile Permanent Magnets

14.10 Artificial Single Domain Particle Magnets (Lodex)

14.11 Bonded Magnets

14.12 Magnet Stability

14.13 Summary of Magnetically Hard Materials

14.14 Applications

15 MAGNETIC MATERIALS FOR RECORDING AND COMPUTERS

15.1 Introduction

15.2 Magnetic Recording

15.3 Principles of Magnetic Recording

15.4 Magnetic Digital Recording

15.5 Perpendicular Recording

15.6 Possible Future Developments

15.7 Magneto-Optic Recording

15.8 Magnetic Memory

16 MAGNETIC PROPERTIES OF SUPERCONDUCTORS

16.1 Introduction

16.2 Type I Superconductors

16.3 Type II Superconductors

16.4 Susceptibility Measurements

16.5 Demagnetizing Effects

APPENDIX 1: DIPOLE FIELDS AND ENERGIES

APPENDIX 2: DATA ON FERROMAGNETIC ELEMENTS

APPENDIX 3: CONVERSION OF UNITS

APPENDIX 4: PHYSICAL CONSTANTS

INDEX

Copyright © 2009 by the Institute of Electrical and Electronics Engineers, Inc.

Published by John Wiley © Sons, Inc., Hoboken, New Jersey. All rights reserved.

Published simultaneously in Canada

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ISBN 978-0-471-47741-9

PREFACE TO THE FIRST EDITION

Take a pocket compass, place it on a table, and watch the needle. It will jiggle around, oscillate, and finally come to rest, pointing more or less north. Therein lie two mysteries. The first is the origin of the earth’s magnetic field, which directs the needle. The second is the origin of the magnetism of the needle, which allows it to be directed. This book is about the second mystery, and a mystery indeed it is, for although a great deal is known about magnetism in general, and about the magnetism of iron in particular, it is still impossible to predict from first principles that iron is strongly magnetic.

This book is for the beginner. By that I mean a senior or first-year graduate student in engineering, who has had only the usual undergraduate courses in physics and materials science taken by all engineers, or anyone else with a similar background. No knowledge of magnetism itself is assumed.

People who become interested in magnetism usually bring quite different backgrounds to their study of the subject. They are metallurgists and physicists, electrical engineers and chemists, geologists and ceramists. Each one has a different amount of knowledge of such fundamentals as atomic theory, crystallography, electric circuits, and crystal chemistry. I have tried to write understandably for all groups. Thus some portions of the book will be extremely elementary for most readers, but not the same portions for all readers.

Despite the popularity of the mks system of units in electricity, the overwhelming majority of magneticians still speak the language of the cgs system, both in the laboratory and in the plant. The student must learn that language sooner or later. This book is therefore written in the cgs system.

The beginner in magnetism is bewildered by a host of strange units and even stranger measurements. The subject is often presented on too theoretical a level, with the result that the student has no real physical understanding of the various quantities involved, simply because he has no clear idea of how these quantities are measured. For this reason methods of measurement are stressed throughout the book. All of the second chapter is devoted to the most common methods, while more specialized techniques are described in appropriate later chapters.

The book is divided into four parts:

1. Units and measurements.

2. Kinds of magnetism, or the difference, for example, between a ferromagnetic and a paramagnetic.

3. Phenomena in strongly magnetic substances, such as anisotropy and magnetostriction.

4. Commercial magnetic materials and their applications.

The references, selected from the enormous literature of magnetism, are mainly of two kinds, review papers and classic papers, together with other references required to buttress particular statements in the text. In addition, a list of books is given, together with brief indications of the kind of material that each contains.

Magnetism has its roots in antiquity. No one knows when the first lodestone, a natural oxide of iron magnetized by a bolt of lightning, was picked up and found to attract bits of other lodestones or pieces of iron. It was a subject bound to attract the superstitious, and it did. In the sixteenth century Gilbert began to formulate some clear principles.

In the late nineteenth and early twentieth centuries came the really great contributions of Curie, Langevin, and Weiss, made over a span of scarcely more than ten years. For the next forty years the study of magnetism can be said to have languished, except for the work of a few devotees who found in the subject that fascinations so eloquently described by the late Professor E. C. Stoner:

The rich diversity of ferromagnetic phenomena, the perennial challenge to skill in experiment and to physical insight in coordinating the results, the vast range of actual and possible applications of ferromagnetic materials, and the fundamental character of the essential theoretical problems raised have all combined to give ferromagnetism a width of interest which contrasts strongly with the apparent narrowness of its subject matter, namely, certain particular properties of a very limited number of substances.

Then, with the end of World War II, came a great revival of interest, and the study of magnetism has never been livelier than it is today. This renewed interest came mainly from three developments:

1. A new material. An entirely new class of magnetic materials, the ferrites, was developed, explained, and put to use.

2. A new tool. Neutron diffraction, which enables us to “see” the magnetic moments of individual atoms, has given new depth to the field of magnetochemistry.

3. A new application. The rise of computers, in which magnetic devices play an essential role, has spurred research on both old and new magnetic materials.

And all this was aided by a better understanding, gained about the same time, of magnetic domains and how they behave.

In writing this book, two thoughts have occurred to me again and again. The first is that magnetism is peculiarly a hidden subject, in the sense that it is all around us, part of our daily lives, and yet most people, including engineers, are unaware or have forgotten that their lives would be utterly different without magnetism. There would be no electric power as we know it, no electric motors, no radio, no TV. If electricity and magnetism are sister sciences, then magnetism is surely the poor relation. The second point concerns the curious reversal, in the United States, of the usual roles of university and industrial laboratories in the area of magnetic research. While Americans have made sizable contributions to the international pool of knowledge of magnetic materials, virtually all of these contributions have come from industry. This is not true of other countries or other subjects. I do not pretend to know the reason for this imbalance, but it would certainly seem to be time for the universities to do their share.

Most technical books, unless written by an authority in the field, are the result of a collaborative effort, and I have had many collaborators. Many people in industry have given freely from their fund of special knowledge and experiences. Many others have kindly given me original photographs. The following have critically read portions of the book or have otherwise helped me with difficult points: Charles W. Allen, Joseph J. Becker, Ami E. Berkowitz, David Cohen, N. F. Fiore, C. D. Graham, Jr., Robert G. Hayes, Eugene W. Henry, Conyers Herring, Gerald L. Jones, Fred E. Luborsky, Walter C. Miller, R. Pauthenet, and E. P. Wohlfarth. To these and all others who have aided in my magnetic education, my best thanks.

B. D. C.

Notre Dame, Indiana

February 1972

PREFACE TO THE SECOND EDITION

B. D. (Barney) Cullity (1917–1978) was a gifted writer on technical topics. He could present complicated subjects in a clear, coherent, concise way that made his books popular with students and teachers alike. His first book, on X-ray diffraction, taught the elements of crystallography and structure and X-rays to generations of metallurgists. It was first published in 1967, with a second edition in 1978 and a third updated version in 2001, by Stuart R. Stock. His book on magnetic materials appeared in 1972 and was similarly successful; it remained in print for many years and was widely used as an introduction to the subjects of magnetism, magnetic measurements, and magnetic materials.

The Magnetics Society of the Institute of Electrical and Electronic Engineers (IEEE) has for a number of years sponsored the reprinting of classic books and papers in the field of magnetism, including perhaps most notably the reprinting in 1993 of R. M. Bozorth’s monumental book Ferromagnetism, first published in 1952. Cullity’s Introduction to Magnetic Materials was another candidate for reprinting, but after some debate it was decided to encourage the production of a revised and updated edition instead. I had for many years entertained the notion of making such a revision, and volunteered for the job. It has taken considerably longer than I anticipated, and I have in the end made fewer changes than might have been expected.

Cullity wrote explicitly for the beginner in magnetism, for an undergraduate student or beginning graduate student with no prior exposure to the subject and with only a general undergraduate knowledge of chemistry, physics, and mathematics. He emphasized measurements and materials, especially materials of engineering importance. His treatment of quantum phenomena is elementary. I have followed the original text quite closely in organization and approach, and have left substantial portions largely unchanged. The major changes include the following:

1. I have used both cgs and SI units throughout, where Cullity chose cgs only. Using both undoubtedly makes for a certain clumsiness and repetition, but if (as I hope) the book remains useful for as many years as the original, SI units will be increasingly important.

2. The treatment of measurements has been considerably revised. The ballistic galvanometer and the moving-coil fluxmeter have been compressed into a single sentence. The electronic integrator appears, along with the alternating-gradient magnetometer, the SQUID, and the use of computers for data collection. No big surprises here.

3. There is a new chapter on magnetic materials for use in computers, and a brief chapter on the magnetic behavior of superconductors.

4. Amorphous magnetic alloys and rare-earth permanent magnets appear, the treatment of domain-wall structure and energy is expanded, and some work on the effect of mechanical stresses on domain wall motion (a topic of special interest to Cullity) has been dropped.

I considered various ways to deal with quantum mechanics. As noted above, Cullity’s treatment is sketchy, and little use is made of quantum phenomena in most of the book. One possibility was simply to drop the subject entirely, and stick to classical physics. The idea of expanding the treatment was quickly dropped. Apart from my personal limitations, I do not believe it is possible to embed a useful textbook on quantum mechanics as a chapter or two in a book that deals mainly with other subjects. In the end, I pretty much stuck with Cullity’s original. It gives some feeling for the subject, without pretending to be rigorous or detailed.

References

All technical book authors, including Cullity in 1972, bemoan the vastness of the technical literature and the impossibility of keeping up with even a fraction of it. In working closely with the book over several years, I became conscious of the fact that it has remained useful even as its many references became obsolete. I also convinced myself that readers of the revised edition will fall mainly into two categories: beginners, who will not need or desire to go beyond what appears in the text; and more advanced students and research workers, who will have easy access to computerized literature searches that will give them up-to-date information on topics of interest rather than the aging references in an aging text. So most of the references have been dropped. Those that remain appear embedded in the text, and are to old original work, or to special sources of information on specific topics, or to recent (in 2007) textbooks. No doubt this decision will disappoint some readers, and perhaps it is simply a manifestation of authorial cowardice, but I felt it was the only practical way to proceed.

I would like to express my thanks to Ron Goldfarb and his colleagues at the National Institute of Science and Technology in Boulder, Colorado, for reading and criticizing the individual chapters. I have adopted most of their suggestions.

C. D. GRAHAM

Philadelphia, Pennsylvania

May 2008