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An IEEE Press Classic Reissue THE PHYSICAL PRINCIPLES OF MAGNETISM IEEE Press 445 Hoes Lane, P.O. Box 1331 Piscataway, NJ 08855-1331 IEEE Press Editorial Board Robert J. Herrick, Editor in Chief M. Akay M. Eden W. D. Reeve J. B. Anderson M. E. El-Hawary M. S. Newman P. M. Anderson R. F. Hoyt M. Padgett J.E. Brewer S.V.Kartalopoulos G. Zobrist D.Kirk Kenneth Moore, Director of IEEE Press Catherine Faduska, Senior Acquisitions Editor Linda Matarazzo, Associate Acquisitions Editor Marilyn Catis, Marketing Manager Mark Morrell, Associate Production Editor IEEE Magnetics Society, Sponsor AP-S Liaison to IEEE Press, Robert Mailloux Cover design: William T. Donnelly, WTDesign Books of Related Interest from the IEEE Press MAGNETIC HYSTERESIS Edward Delia Torre 1999 Softcover 240 pp IEEE Order No. PP5766 ISBN 0-7803-6041-9 MAGNETO-OPTICAL RECORDING MATERIALS Edited by Richard J. Gambino and Takao Suzuki 2000 Hardcover 464 pp IEEE Order No. PC3582 ISBN 0-7803-1009-8 MAGNETIC RECORDING: The First 100 Years Edited by Eric D. Daniel, C. Denis Mee, and Mark H. Clark 1999 Softcover 360 pp IEEE Order No. PP5396 ISBN 0-7803-4709-9 MAGNETIC RECORDING TECHNOLOGY, Second Edition C. Denis Mee and Eric D. Daniel 1996 Hardcover 750 pp IEEE Order No. PC5659 ISBN 0-07-041276-6 MAGNETIC STORAGE HANDBOOK, Second Edition C. Denis Mee and Eric D. Daniel 1997 Hardcover 752 pp IEEE Order No. PC5688 ISBN 0-07-041275-8 FERROMAGNETISM: An IEEE Press Classic Reissue Richard M. Bozorth 1994 Hardcover 992 pp IEEE Order No. PC3814 ISBN 0-7803-1032-2 An IEEE Press Classic Reissue THE PHYSICAL PRINCIPLES OF MAGNETISM Allan H. Morrish Department of Physics and Astronomy University of Manitoba, Canada IEEE Magnetics Society, Sponsor IEEE PRESS The Institute of Electrical and Electronics Engineers, New York This book and other books may be purchased at a discount from the publisher when ordered in bulk quantities. Contact: IEEE Press Marketing Attn: Special Sales 445 Hoes Lane, P.O. Box 1331 Piscataway, NJ 08855-1331 Fax: +1 732 981 9334 For more information about IEEE Press products, visit the IEEE Online Catalog & Store: http://www.ieee.org/store. Original edition in 1965, published by John Wiley & Sons, Inc. Reprinted in 1980 byRobert E. Krieger Publishing Company, Inc. © 2001 by The Institute of Electrical and Electronics Engineers, Inc. 3 Park Avenue, 17th Floor, New York, NY 10016-5997 All rights reserved. No part of this book may be reproduced in any form, nor may it be stored in a retrieval system or transmitted in any form, without written permission from the publisher. 10 9 8 7 6 5 4 3 21 ISBN 0-7803-6029-X IEEE Order No. PC5877 Library of Congress Cataloging-in-Publication Data Morrish, Allan H. The physical principles of magnetism / Allan H. Morrish. p. cm. Originally published: New York : Wiley, 1965, in series: Wiley series on the science and technology of materials. "An ΓΕΕΕ Press classic reissue." "IEEE order no. PC5877"~T.p. verso. Includes bibliographical references and indexes. ISBN 0-7803-6029-X 1. Magnetism. I. Title. QC753.2 .M67 2001 538»dc21 00-053912 To My Parents Foreword to the Classic Reissue The IEEE Magnetics Society has embarked on a program of reissues of classic works in magnetism. These books have served as an invaluable resource for understanding magnetic phenomena. The Physical Principles of Magnetism by Allan Henry Morrish is such a classic—a comprehensive introduction to all aspects of magnetism. Since its publication in 1965, it has been used by many scientists to learn the basics of magnetism in considerable depth. The corrected reissue is a welcome addition to this much-needed archival series. Dr. Morrish presents an excellent introduction to the physics and mathemat- ics of magnetism without oversimplification. Although great progress has been made in technology in the 35 years since it first appeared in print, the basic principles of magnetism are unchanged. This respected and timeless classic book clearly elucidates these principles. Dr. Morrish is a distinguished professor of physics at the University of Manitoba. He is a fellow of The Royal Society of Canada and The Institute of Physics (U.K.), as well as a former fellow of The American Physical Society. Also, he was president of The Canadian Association of Physicists and was awarded their gold medal for achievements in physics. A prolific researcher, Dr. Morrish has written over 250 papers and served on many national and interna- tional committees. It is with great pleasure that we welcome this book back in print. Edward Delia Torre The George Washington University President of the IEEE Magnetics Society Preface Whatever else may be said concerning the two decades following World War II, they have been wonderful years for science. All of the scientific countries of the world have contributed to the great increase in knowledge. Although advances have been made in almost all areas, some have been favored over others. One of the subjects that has received the greatest attention is that of magnetism. Although the appearance of a vast amount of literature is in itself laudable, it has created educational problems. The scientist or engineer who desires or requires an integrated knowledge of magnetism has found it increasingly difficult to satisfy this need. This book was written with such readers primarily in mind. The material between these covers has formed the basis for several solid state courses offered at the University of Minnesota since 1958. Some of the more elementary parts have been employed for the third quarter of a first course in solid state physics. However, the major use of this text has been as a three-quarter graduate course in magnetism. The students attending the lectures have come from chemistry, physics, electrical engineering, physical metallurgy, and geophysics departments. Since the backgrounds of the audience varied so much, the course was developed by starting as far as possible from first principles. However, it was necessary to begin somewhere, and consequently, first courses in solid state physics and quantum mechanics were usually assumed as prerequisites. Magnetic phenomena are discussed both from an experimental and theoretical point of view. The plan has been first to present the underlying physical principles and then to follow up with appropriate macroscopic or microscopic theories. Although quantum mechanical theories are given, a phenomenological approach is emphasized. More than half the vli viii PREFACE book is devoted to a discussion of strongly coupled dipole systems, and in this area the molecular field theory is stressed. The principles and theories have been illustrated by selections from the experimental data, and various tables have been included in. an attempt to give some idea of the scope of the literature. Very few references to 1964 papers are included because of publication deadlines. The utter impossibility of completely surveying all aspects of the subject may be illustrated by considering the 1964 Magnetic Materials Digest.1 This publication, which attempts to summarize the 1963 literature per- taining to fundamental studies of ordered magnetic materials, contains more than 1700 references! The particular topics chosen to be discussed at greatest length in this book were determined, as it is usually put, by my own interests. This, of course, really means my own knowledge, experience, talents, and limitations as shaped by contact with colleagues, teaching assignments, and availability of research and travel grants. The coverage of some topics, for example alloys and superconductivity, inadequately reflects the number and extent of current investigations. Other topics, for example, magnetohydrodynamics, group theoretical analysis, and the magnetoelectric effect, have been completely omitted. Nevertheless, the book is rather long and indeed contains more material than can normally be covered in a one-year course. The question of notation has been a vexing problem. In a book as comprehensive as this one, there are simply not enough symbols to go around. A partial solution has been sought in the use of different kinds of type for the same letter. For example, μ and μ represent the dipole magnetic moment and the permeability, H and 3t represent the magnetic field and Hamiltonian, and D, D, and Ϊ) represent the demagnetizing factor, the crystal field spin parameter, and the Dzialoshinski vector, respectively. Even so, it was found necessary sometimes to employ the same symbol for more than one quantity; it is only hoped that the context will reduce, if not entirely remove, the danger of ambiguity. Although in general I have tried to adhere to the symbols commonly found in the literature, some deliberate departures have been made. In publications on nuclear magnetic resonance, and to some degree in electron para- magnetic resonance, T with some subscript denotes relaxation time. However, I prefer to reserve T for either temperature or period of time and have therefore taken the liberty of representing relaxation times by T plus a subscript; this usage at least has the merit of being consistent with that in all other branches of science and engineering. Other, though less important examples, include the use of M for the magnetization H 1 A. H. Morrish, R. J. Prosen, and S. M. Rubens, editors, 1964 Magnetic Materials Digest, M. W. Lads Publishing Co., Philadelphia, Pa. (1964). PREFACE ix along the direction of an applied field, Ηχ for the amplitude of an alter- nating magnetic field, H for the effective magnetic field, H for e m the molecular field, J for an exchange interaction constant, T for the e FN Neel temperature of a ferrimagnet, and N with some subscript for the Weiss molecular field constants. For the Bohr magneton a choice between μ and β was possible; I have selected μ mainly because ß also represents Β Β an angle or the relativistic quantity v\c. I have substituted the term "uncompensated poles" for "free poles," since the latter may be taken to imply the existence of monopoles, and they have never been observed in nature. The phrase "intensity of magnetization," common in the British literature, has been eliminated on the grounds that it is both inappropriate and inept. The symbol e for the elementary electric charge represents either type; that is, a negative number is to be substituted for an electron and a positive number for a proton or positron. Except as otherwise noted, the gaussian cgs system of units is employed. There remains the pleasant task of thanking those who have played some role in the production of this book. I am very grateful to Professor A. J. Dekker, now at Groningen, The Netherlands, who first interested me in doing research in solid state physics and who encouraged me to write this book. I have been fortunate in having Professor W. F. Brown, Jr., as a colleague during part of my tenure at the University of Minnesota. The discussions we have had have left their imprint on a number of these pages. In addition, a critical reading of the first chapter by Dr. Brown has led to its improvement. The response and comments of my graduate students have greatly aided me in the removal of errors, incon- sistencies, and obscurities. They have also demonstrated that almost all the problems are soluble. I am indebted to the many publishers and individuals who have given me permission to reproduce figures and tables; these sources are acknowledged at the pertinent places in the text. Finally, I wish to thank my wife for her help with the arduous tasks of proofreading and index preparation. University of Manitoba ALLAN H. MORRISH Winnipeg, Canada April 1965