Technology & Engineering
Ferromagnetic Materials
Ferromagnetic materials are substances that exhibit strong magnetic properties, such as iron, nickel, and cobalt. They can be magnetized and retain their magnetization, making them useful in a wide range of technological applications, including electric motors, transformers, and magnetic storage devices. These materials are characterized by their ability to form permanent magnets and to attract other ferromagnetic materials.
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10 Key excerpts on "Ferromagnetic Materials"
eBook - PDF- D.F. Warne(Author)
- 2005(Publication Date)
- Newnes(Publisher)
Ferromagnetic properties are confined almost entirely to iron, nickel and cobalt and their alloys. The only exceptions are some alloys of manganese and some of the rare earth elements. Ferrimagnetism is the magnetism of the mixed oxides of the ferromagnetic elements. These are variously called ferrites and garnets. The basic ferrite is magnetite, or Fe 3 O 4 , which can be written as FeO . Fe 2 O 3 . By substituting the FeO with other divalent oxides, a wide range of compounds with useful properties can be produced. The main advantage of these materials is that they have high electrical resistivity which mini- mizes eddy currents when they are used at high frequencies. The important parameters in magnetic materials can be defined as follows: ● permeability – this is the flux density B per unit of magnetic field H, as defined in eqns 2.14 and 2.15. It is usual and more convenient to quote the value of relative permeability µ r , which is B/µ o H. A curve showing the variation of per- meability with magnetic field for a ferromagnetic material is given in Fig. 3.1. This is derived from the initial magnetization curve and it indicates that the per- meability is a variable which is dependent on the magnetic field. The two important values are the initial permeability, which is the slope of the magneti- zation curve at H = 0, and the maximum permeability, corresponding to the knee of the magnetization curve. ● saturation – when sufficient field is applied to a magnetic material it becomes saturated. Any further increase in the field will not increase the magnetization and any increase in the flux density will be due to the added field. The satura- tion magnetization is M s in amperes per metre and J s or B s in tesla. ● remanence, B r and coercivity, H c – these are the points on the hysteresis loop shown in Fig. 3.2 at which the field H is zero and the flux density B is zero, respectively. It is assumed that in passing round this loop, the material has been saturated.
- Donald Askeland, Wendelin Wright, Donald Askeland(Authors)
- 2020(Publication Date)
- Cengage Learning EMEA(Publisher)
Magnetic Materials C H A P T E R 20 Have You Ever Wondered? ● What affects the “lifting strength” of a magnet? ● What are “soft” and “hard” magnetic materials? ● Are there “nonmagnetic” materials? ● Are there materials that develop mechanical strain upon the application of a magnetic field? Chapter Learning Objectives The key objectives of this chapter are to ● Define the terms ferromagnetic, ferrimagnetic, paramagnetic, diamagnetic, anti-ferromagnetic, and superparamagnetic. ● Explain the physical basis for the magnetic behavior of elements based on electron spin and orbital motion of electrons around the nucleus. ● Calculate magnetic field and inductance. ● Define the terms magnetic permeability of vacuum, relative permeability of a material, and magnetic susceptibility. ● Describe the movement of domains in a magnetic field and the accompanying change in magnetization due to an increase in the applied magnetic field. ● Identify saturation magnetization, remanance, and coercive field on ferromagnetic hysteresis loops. E very material in the world responds to the presence of a magnetic field. Magnetic materials are used to construct such things as electrical motors, generators, and transformers. Much of data storage technology (computer hard disks, computer disks, and the like) is based on magnetic particles. Magnetic materials are also used in loudspeakers, microphones, land-line telephones, and tape - based video recorders. Magnetic materials, such as iron oxide (Fe 3 O 4 ) particles, are Copyright 2022 Cengage Learning. All Rights Reserved. May not be copied, scanned, or duplicated, in whole or in part. Due to electronic rights, some third party content may be suppressed from the eBook and/or eChapter(s). Editorial review has deemed that any suppressed content does not materially affect the overall learning experience. Cengage Learning reserves the right to remove additional content at any time if subsequent rights restrictions require it.
eBook - PDFFundamentals of Materials Science and Engineering
An Integrated Approach
- William D. Callister, Jr., David G. Rethwisch(Authors)
- 2016(Publication Date)
- Wiley(Publisher)
18.4 Ferromagnetism • 781 18.4 FERROMAGNETISM Certain metallic materials possess a permanent magnetic moment in the absence of an external field and manifest very large and permanent magnetizations. These are the characteristics of ferromagnetism, and they are displayed by the transition metals iron (as BCC -ferrite), cobalt, nickel, and some rare earth metals such as gadolinium (Gd). Magnetic susceptibilities as high as 10 6 are possible for Ferromagnetic Materials. Consequently, H << M, and from Equation 18.5 we write B ≅ μ 0 M (18.8) Permanent magnetic moments in Ferromagnetic Materials result from atomic mag- netic moments due to uncanceled electron spins as a consequence of the electron struc- ture. There is also an orbital magnetic moment contribution that is small in comparison to the spin moment. Furthermore, in a ferromagnetic material, coupling interactions cause net spin magnetic moments of adjacent atoms to align with one another, even in the absence of an external field. This is schematically illustrated in Figure 18.7. The origin of these coupling forces is not completely understood, but they are thought to arise from the electronic structure of the metal. This mutual spin alignment exists over relatively large-volume regions of the crystal called domains (see Section 18.7). The maximum possible magnetization, or saturation magnetization, M s , of a fer- romagnetic material represents the magnetization that results when all the magnetic dipoles in a solid piece are mutually aligned with the external field; there is also a corresponding saturation flux density, B s . The saturation magnetization is equal to the product of the net magnetic moment for each atom and the number of atoms present. For each of iron, cobalt, and nickel, the net magnetic moments per atom are 2.22, 1.72, and 0.60 Bohr magnetons, respectively.
eBook - PDFFundamentals of Materials Science and Engineering
An Integrated Approach
- William D. Callister, Jr., David G. Rethwisch(Authors)
- 2016(Publication Date)
- Wiley(Publisher)
18.4 Ferromagnetism • 781 18.4 FERROMAGNETISM Certain metallic materials possess a permanent magnetic moment in the absence of an external field and manifest very large and permanent magnetizations. These are the characteristics of ferromagnetism, and they are displayed by the transition metals iron (as BCC -ferrite), cobalt, nickel, and some rare earth metals such as gadolinium (Gd). Magnetic susceptibilities as high as 10 6 are possible for Ferromagnetic Materials. Consequently, H << M, and from Equation 18.5 we write B ≅ μ 0 M (18.8) Permanent magnetic moments in Ferromagnetic Materials result from atomic mag- netic moments due to uncanceled electron spins as a consequence of the electron struc- ture. There is also an orbital magnetic moment contribution that is small in comparison to the spin moment. Furthermore, in a ferromagnetic material, coupling interactions cause net spin magnetic moments of adjacent atoms to align with one another, even in the absence of an external field. This is schematically illustrated in Figure 18.7. The origin of these coupling forces is not completely understood, but they are thought to arise from the electronic structure of the metal. This mutual spin alignment exists over relatively large-volume regions of the crystal called domains (see Section 18.7). The maximum possible magnetization, or saturation magnetization, M s , of a fer- romagnetic material represents the magnetization that results when all the magnetic dipoles in a solid piece are mutually aligned with the external field; there is also a corresponding saturation flux density, B s . The saturation magnetization is equal to the product of the net magnetic moment for each atom and the number of atoms present. For each of iron, cobalt, and nickel, the net magnetic moments per atom are 2.22, 1.72, and 0.60 Bohr magnetons, respectively.
eBook - PDFFundamentals of Materials Science and Engineering
An Integrated Approach
- William D. Callister, Jr., David G. Rethwisch(Authors)
- 2022(Publication Date)
- Wiley(Publisher)
4. In terms of crystal structure, explain the source of ferrimagnetism for cubic ferrites. 5. (a) Describe magnetic hysteresis; (b) explain why ferromagnetic and ferrimagnetic ma- terials experience magnetic hysteresis; and (c) explain why these materials may become permanent magnets. 6. Note the distinctive magnetic characteristics for both soft and hard magnetic materials. 7. Describe the phenomenon of superconductivity. Magnetism—the phenomenon by which materials exert an attractive or repulsive force or influence on other materials—has been known for thousands of years. However, the underlying principles and mechanisms that explain magnetic phenomena are complex and subtle, and their understanding has eluded scientists until relatively recent times. Many modern technological devices rely on magnetism and magnetic materials, including electrical power generators and transformers, electric motors, radio, television, tele- phones, computers, and components of sound and video reproduction systems. Iron, some steels, and the naturally occurring mineral lodestone are well-known examples of materials that exhibit magnetic properties. Not so familiar, however, is the fact that all substances are influenced to one degree or another by the presence of a mag- netic field. This chapter provides a brief description of the origin of magnetic fields and discusses magnetic field vectors and magnetic parameters; diamagnetism, paramagnetism, ferromagnetism, and ferrimagnetism; different magnetic materials; and superconductivity. 18.1 | | INTRODUCTION 18.2 | | BASIC CONCEPTS Magnetic Dipoles Magnetic forces are generated by moving electrically charged particles; these magnetic forces are in addition to any electrostatic forces that may exist. Often it is convenient to think of magnetic forces in terms of fields. Imaginary lines of force may be drawn to indicate the direction of the force at positions in the vicinity of the field source.
eBook - PDFElectrons, Neutrons and Protons in Engineering
A Study of Engineering Materials and Processes Whose Characteristics May Be Explained by Considering the Behavior of Small Particles When Grouped Into Systems Such as Nuclei, Atoms, Gases, and Crystals
- J. R. Eaton(Author)
- 2013(Publication Date)
- Pergamon(Publisher)
CHAPTER 20 MAGNETIC PROPERTIES OF MATERIALS MAGNETIC materials find a wide range of application in science and industry, being used in the construction of transformers, generators, relays, loud speakers, electrical instruments and many other devices. An estimated hundred million dollars'-worth of magnetic steel is used each year by the electrical industry, and the power losses occasioned by their use in operating equipment cost perhaps two hundred million dollars per year. It is at once obvious that magnetic ma-terials are of great economic significance. The early developments in magnetic materials came about as a result of the intuition and experimentation of the metallurgists, who made advances with but little theoretical guidance. The first scientific studies in this field were at-tempts to find theories to explain the behavior of the materials which had been in existence for some time. As the theory developed, means of improving exist-ing materials soon became evident; and with increased theoretical knowledge, new types of materials were predicted and eventually produced. As a result of theoretical and experimental advances, magnetic materials are available today which have characteristics far superior to those which were known before theoretical study had made significant progress. 20.1. T H E O R I G I N OF THE M A G N E T I C BEHAVIOR OF MATERIALS If a magnetic intensity H exists in free space a flux-density B will be observed such that B 0 = μ 0 Η (20.1) where μ 0 is the permeability of free space. If the same intensity //exists in a material of permeability μ, the flux density will be B = μΗ (20.2) where B may be greater or less than B 0 · It is sometimes desirable to rewrite Equation (20.2) in the form B = μ 0 Η + (μ -μ 0 )Η. (20.3) 388 MAGNETIC PROPERTIES OF MATERIALS 389 The term (μ — μ 0 )Η, known as the intensity of magnetization, may be attribu-ted to the response of the material to the applied magnetic intensity.
eBook - PDF- G R Jones(Author)
- 2013(Publication Date)
- Newnes(Publisher)
The magnetic properties of Ferromagnetic Materials depend not only on their chemical composition, but also on the mechanical working and heat treatment that they have under-gone. For practical purposes magnetic materials fall into two main groups, high permeability or soft magnetic materials and permanent magnet or hard magnetic materials. There are a number of groups of soft magnetic materials including soft iron, mild steel, silicon steels, nickel iron alloys and ferrites. In static d.c. applications mild steel is the main bulk material, but where better properties are required with higher magnetic permeability, soft iron is used. Silicon steel is the major bulk material for low frequency alternating field applications and the nickel irons are used for more specialised applications with the soft ferrites being applied at the higher frequencies because of their high resistivity. There are four main classes of permanent-magnet materials: steels, Alnicos, hard ferrites (also called ceramics) and rare-earth alloys. Of these the steels are almost obsolete because of their inferior properties and, during the last 25 years, the ferrites have gradually taken over from the Alnicos as the main bulk material, principally because of their cost advantage. The rare-earth alloys, which are a more recent development are finding increasing numbers of applications because of their much superior properties enabling considerable weight and space saving to be made where cost is not of paramount importance. 14.2 Electrical steels including silicon steels 14.2.1 General Electrical steels form a class of sheet material used for the flux-carrying cores of transformers, motors, generators, sol-enoids and other electromechanical devices. Almost always alternating magnetisation is employed and the material is designed to keep power losses due to eddy currents and magnetic hysteresis to a minimum.
eBook - PDFFundamentals of Materials Science and Engineering
An Integrated Approach
- William D. Callister, Jr., David G. Rethwisch(Authors)
- 2021(Publication Date)
- Wiley(Publisher)
6. Note the distinctive magnetic characteristics for both soft and hard magnetic materials. 7. Describe the phenomenon of superconductivity. Magnetism—the phenomenon by which materials exert an attractive or repulsive force or influence on other materials—has been known for thousands of years. However, the underlying principles and mechanisms that explain magnetic phenomena are complex and subtle, and their understanding has eluded scientists until relatively recent times. Many modern technological devices rely on magnetism and magnetic materials, including electrical power generators and transformers, electric motors, radio, television, tele- phones, computers, and components of sound and video reproduction systems. Iron, some steels, and the naturally occurring mineral lodestone are well-known examples of materials that exhibit magnetic properties. Not so familiar, however, is the fact that all substances are influenced to one degree or another by the presence of a magnetic field. This chapter provides a brief description of the origin of magnetic fields and discusses magnetic field vectors and magnetic parameters; diamagnetism, paramagnetism, ferromagnetism, and ferrimagnetism; different magnetic materials; and superconductivity. 18.1 INTRODUCTION Magnetic Dipoles Magnetic forces are generated by moving electrically charged particles; these magnetic forces are in addition to any electrostatic forces that may exist. Often it is convenient to think of magnetic forces in terms of fields. Imaginary lines of force may be drawn to indicate the direction of the force at positions in the vicinity of the field source. The magnetic field distributions as indicated by lines of force are shown for a current loop and a bar magnet in Figure 18.1. Magnetic dipoles are found to exist in magnetic materials and in some respects are analogous to electric dipoles (Section 12.19).
- Robert J. Naumann(Author)
- 2008(Publication Date)
- CRC Press(Publisher)
25 Magnetism and Magnetic Materials Magnetism may be thought of as electricity in motion. It is actually a relativistic effect of moving charges according to Einstein ’ s special theory of relativity. One observes a mag-netic fi eld in a reference frame that electrons are fl owing through, but in a reference frame that moves with the electrons, one observes only an electric fi eld. Natural ferromagnets in the form of loadstones were known to the ancient Chinese who used them for navigation. Hans Christian Ørsted was the fi rst person to connect magnetism with electricity when he noticed that a fl owing current in fl uenced a compass needle. Magnetic materials continue to play an ever increasing role in our modern technical society. For example, the recent discovery of low-cost iron-neodymium-boron magnets has made it possible to build highly ef fi cient permanent magnet motors that are used in hybrid vehicles and will be used in future electric vehicles. Another example is the continued development of magnetic storage media, which have extended hard drive storage capaci-ties far beyond what anyone would have expected a decade ago and have made high performance computers affordable to almost everyone. In order to understand how these materials function, we need to start with some basic principles. 25.1 Basic Relationships Just as the capacitance was increased when a dielectric with polarization P was placed between the plates of a capacitor, the magnetic fi eld in, or in the vicinity of, a material is altered by the magnetization M of the material. By analogy with the electric fi eld case in which we wrote D ¼ « E , we can write for the case of the magnetism B ¼ m H , where H is the applied magnetic fi eld (A = m), B is the resulting fl ux density (V s = m 2 ¼ Wb = m 2 ¼ T), and m is the permeability of the medium.
eBook - PDF- William F. Gale, Terry C. Totemeier(Authors)
- 2003(Publication Date)
- Butterworth-Heinemann(Publisher)
and V. K. Pecharsky, ‘Magnetocaloric Materials’, Annu. Rev. Mater. Sci ., 30 , 387–429, 2000. 30. C. A. Ross, ‘Patterned Magnetic Recording Media’, Annu. Rev. Mater. Sci ., 31 , 203–235, 2001. 31. K. H. J. Buschow, ‘Permanent-magnet materials and their applications’, Mater. Sci. Found ., 5 , 1–82, 1998. High-permeability materials (Si-Fe, Ni-Fe and Ferrites) 32. M. G. Say, G. R. Jones and M. A. Laughton, ‘Electrical Engineers Reference Book’, 15th Edn, Butterworths, 1993. 33. R. Boll, ‘Soft Magnetic Materials: fundamentals, product, applications’, Siemens, 1979. 34. E. C. Snelling, ‘Soft Ferrites, Properties and Applications’, 2nd Edn, Butterworths, 1989. 35. E. C. Snelling and A. D. Giles, ‘Ferrites for Inductors and Transformers’, Research Studies Press, 1986. 36. B. Lax and K. J. Button, ‘Microwave Ferrites and Ferrimagnetics’, McGraw Hill, 1962. Non-magnetic steels and cast irons 37. C. B. Post and W. S. Eberly, ‘Stability of austenite in stainless steel’, Trans. Am. Soc. Metals , 39 , 868, 1947. Standards 38. A series of International (IEC) and equivalent British Standards (BS) have been published for the Classifi-cation, Specification and Methods of Test for Magnetic Materials. The IEC series are numbered 404 and the equivalent BS series are 6404. In addition BS 4727, part I Group 07, 1991 is the standard for ‘Magnetism terminology’ and BS 5884, 1987. Methods for determination of relative magnetic permeability of feebly magnetic materials.
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