Magnetism and Metallurgy of Soft Magnetic Materials

Chih-Wen Chen

• Publisher: Dover Publications
• Year: 2013
• Print ISBN: 9780486649979
• eBook ISBN: 9780486145136
• Topic: Physical Sciences
• Subtopic: Physics
• Index: Physics

Soft magnetic materials are economically and technologically the most important of all magnetic materials. In particular, the development of new materials and novel applications for the computer and telecommunications industries during the past few decades has immensely broadened the scope and altered the nature of soft magnetic materials. In addition to metallic substances, nonmetallic compounds and amorphous thin films are coming increasingly important. This thorough, well-organized volume — on of the most comprehensive treatments available — offers a coherent, logical presentation of the physical principles underlying both the intrinsic and applied properties of soft magnetism. Two basic components are stressed: (1) traditional magnetism, which imparts magnetization and spin-dependent properties, and (2) metallurgy, which governs the preparation of the products and the attainment of their structure-sensitive properties. The book comprises seven major chapters: Introduction; Ferromagnetism and Ferrimagnetism; Magnetization and Domain Structure; Magnetic Properties; Metallurgy of Soft Magnetic Materials; Applications of Soft Magnetic Materials; and Special Topics (radiation effects and magnetic bubbles and devices).
In addition to an extensive introduction to the basic principles of magnetism relevant to all magnetic materials (Chapters I-IV), Professor Chen (Lawrence Livermore National Laboratory) devotes the core of the book to a rigorous, detailed discussion of the effects of metallurgical factors such as purity, alloying, grain structure, defects, and atomic order on the properties and performance of magnetic metals, alloys, and compounds. An extensive and important chapter on the special topics of magnetic bubbles and radiation effects rounds out this timely and wide-ranging survey of a crucial topic in solid state physics.
Written for materials scientists, experimental physicists, and metallurgists, the book also lends itself to use as a textbook for graduate courses in magnetic materials.

CHAPTER 1

INTRODUCTION

§1. HISTORICAL

The history of the development of magnetic materials is undeniably long and splendid. According to the history of Asia Minor, a cradle of civilization, lodestone was discovered as a natural magnet in Magnesia more than 3500 years ago. The stone was called magnes lapis, which means Magnesian stone. “Magnet” and “magnetism” were derived from the word “Magnesian.” Thales of Miletus, the Greek philosopher, stated that the magnetic interaction between magnetite and iron was known before 600 BC. Contemporary Chinese historians have shown evidence that the world’s first compass—a south-point spoon of lodestone balanced on a round, bronze heaven plate within a square earth plate—was invented in China about 85 AD (see figure at left).

Magnetic materials also played a prominent role in the discovery of the New World and in the development of modern technology. Without the compass Christopher Columbus would not have made his voyages and discoveries. The outstanding magnetic properties and low cost of iron have made it possible to generate inexpensive electricity on a massive scale since 1886 when Westinghouse Electric Company built the first commercial AC generating station at Buffalo, New York. The use of magnetic materials to perform vital functions is not limited to the utility industry, other industries consuming appreciable amounts of magnetic materials include communications, computer, audio-visual, and home appliances, to name just a few.

From the scientific viewpoint, it is understandable that magnetic materials have contributed vitally to the history of civilization and technology. In the first place, all substances, whether solid, liquid or gas, display certain magnetic characteristics at all temperatures. Hence magnetism is one of the basic properties of materials. Secondly, although only three elements (Fe, Co, and Ni) out of a total of 106 are ferromagnetic at room temperature, we are fortunate that iron constitutes approximately 3.3% of the earth’s crust, and hence, it is abundant in natural resources and relatively inexpensive. Thirdly, metallic meteorites are known to consist largely of pure iron. It is logical to assume that, by the time ancient man appeared on the earth, pure iron had already existed for millions of years. The natural occurrence of Fe₃O₄ as lodestone is just as old as meteorites and probably more widespread than the latter. Thus it is not surprising that the magic stone and pure iron were used so early in our history.

Magnetism appears in various forms, as will be discussed in §4; but the kinds that have practical value, and therefore interest us here, are known as ferromagnetism and ferrimagnetism. Traditionally, only those elements that exhibit ferromagnetic properties are called magnetic. Besides Fe, Co and Ni, six elements in the lanthanide series (Gd, Tb, Dy, Ho, Er and Tm) become ferromagnetic at ≈ 20°C (Gd) and subzero temperatures. The list of magnetic materials, nevertheless, is infinitely long because an unlimited number of magnetic solid solutions and compounds can be formed of magnetic and certain nonmagnetic elements.

Soft magnetic material is more a technical term than a scientific one. The word “soft” means temporary in the sense that the ferromagnetism emerges only when a magnetic field is applied. In contrast, hard or permanent magnets display ferromagnetism in the absence of an external field¹. All magnetic elements in the pure form are soft; whereas magnetic solid solutions and compounds can be either soft or hard, depending on the composition and metallurgical treatments. In this book, we are concerned mainly with soft magnetic materials. However, the physical principles discussed in this book are also applicable to hard magnets.

§2. UNITS

In accordance with the 1960 adoption by the Conference Générale de Poids et Mesures (Chiswell and Grigg [1971]), the Système International (SI) d’Unités is used throughout the book. This system is based on the metre–kilogram–second–ampere (MKSA) system. It includes such practical units as ampere, volt and ohm; hence, it is particularly convenient when eddy currents and other phenomena relating magnetism to electricity are discussed. The system offers another advantage in t...

Table of contents

• Title Page
• Copyright Page
• Dedication
• PREFACE
• ACKNOWLEDGEMENTS
• LIST OF MOST IMPORTANT SYMBOLS
• Table of Contents
• CHAPTER 1 - INTRODUCTION
• CHAPTER 2 - FERROMAGNETISM AND FERRIMAGNETISM
• CHAPTER 3 - MAGNETIZATION AND DOMAIN STRUCTURE
• CHAPTER 4 - MAGNETIC PROPERTIES
• CHAPTER 5 - METALLURGY OF SOFT MAGNETIC MATERIALS
• CHAPTER 6 - APPLICATIONS OF SOFT MAGNETIC MATERIALS
• CHAPTER 7 - SPECIAL TOPICS
• APPENDIX 1
• APPENDIX 2
• APPENDIX 3 - DEMAGNETIZING FACTOR AND MAGNETOSTATIC ENERGY
• REFERENCES
• AUTHOR INDEX
• SUBJECT INDEX
• MATERIALS INDEX