Physics
Ferromagnetism
Ferromagnetism is a phenomenon in which certain materials, such as iron, exhibit strong permanent magnetization. This occurs due to the alignment of magnetic moments within the material, resulting in a net magnetic field. Below a specific temperature called the Curie temperature, ferromagnetic materials can retain their magnetization without an external magnetic field, making them useful for various applications in technology and industry.
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10 Key excerpts on "Ferromagnetism"
eBook - PDFMaterials Science and Engineering
An Introduction
- William D. Callister, Jr., David G. Rethwisch(Authors)
- 2018(Publication Date)
- Wiley(Publisher)
20.4 Ferromagnetism • 721 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 20.5 we write B ≅ 0 M (20.8) 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 20.7. 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 20.7). 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.
- William D. Callister, Jr., David G. Rethwisch(Authors)
- 2020(Publication Date)
- Wiley(Publisher)
20.4 Ferromagnetism • 765 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 20.5 we write B ≅ 0 M (20.8) 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 20.7. 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 20.7). 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)
- 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 - PDF- Pierce W. Selwood(Author)
- 2013(Publication Date)
- Academic Press(Publisher)
CHAPTER II Introduction to Magnetism 1. Magnetic Phenomena 1 The reader may find it to be a convenience if there is given a general description of effects related to magnetic fields, so far as these are of concern to our chief purpose. This description will be followed by some definitions, and by some relations between mag-netism and atomic structure. Experience tells us that in the neighborhood of a magnet, or of an electric current as in a piece of wire, space has some unique properties. The properties include the ability to attract a piece of iron and to orient a compass needle. These effects are said to be caused by a magnetic field. A magnetic field has both strength and direction. Some substances have this property that when placed in a mag-netic field which has a gradient of strength from point to point they are repelled to a region of weaker field strength. Such sub-stances, of which water is an example, are said to be diamagnetic. Other substances have the property of being attracted to a region of higher magnetic field strength. Such substances, of which mo-lecular oxygen is an example, are said to be paramagnetic. Some substances are not only strongly attracted to a region of higher field strength, but they themselves have the ability to create quite large magnetic fields, even in the absence of an external field. These substances, of which iron is an example, are said to be ferro-magnetic. A few specialized kinds of magnetic behavior will be referred to later, but our chief interest will be with Ferromagnetism and paramagnetism, and the border region between them. It will be of most service to readers concerned with the phe-nomena of adsorption if we use the cgs and practical system of 19 20 II. INTRODUCTION TO MAGNETISM units. In this system the unit of magnetic field strength, H, is given in oersteds. The oersted has the dimensions cm~ 1/2 g 1/2 sec _1 . A body of matter placed in a magnetic field is said to be mag-netized.
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 - 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).
No longer available |Learn more- (Author)
- 2014(Publication Date)
- Learning Press(Publisher)
________________________ WORLD TECHNOLOGIES ________________________ Chapter- 1 Explanation of Ferromagnetism The Bohr–van Leeuwen theorem shows that magnetism cannot occur in purely classical solids. Without quantum mechanics, there would be no diamagnetism, paramagnetism or Ferromagnetism. The property of Ferromagnetism is due to the direct influence of two effects from quantum mechanics: spin and the Pauli exclusion principle. Origin of magnetism The spin of an electron, combined with its electric charge, results in a magnetic dipole moment and creates a small magnetic field. Although an electron can be visualized classically as a spinning ball of charge, spin is actually a quantum mechanical property with differences from the classical picture, such as the fact that it is quantized into discrete up/down states. The spin of the electrons in atoms is the main source of Ferromagnetism, although there is also some contribution from the orbital angular momentum of the electron about the nucleus, whose classical analogy is a current loop. However in many materials (specifically, those with a filled electron shell), the total dipole moment of all the electrons is zero because the spins are in up/down pairs. Only atoms with partially filled shells (i.e., unpaired spins) can have a net magnetic moment, so Ferromagnetism only occurs in materials with partially filled shells. Because of Hund's rules, the first few electrons in a shell tend to have the same spin, thereby increasing the total dipole moment. When these tiny magnetic dipoles are aligned in the same direction, their individual magnetic fields add together to create a measurable macroscopic field. These unpaired dipoles (often called simply spins even though they also generally include angular momentum) tend to align in parallel to an external magnetic field, an effect called paramagnetism.
eBook - PDFIntroduction to the Theory of Magnetism
International Series of Monographs in Natural Philosophy
- D. Wagner, D. Ter Haar(Authors)
- 2013(Publication Date)
- Pergamon(Publisher)
III. Ferromagnetism 1. Interactions Ferromagnetism, antiFerromagnetism, and ferrimagnetism are mag-netic phenomena, which differ essentially from the diamagnetism and paragnetism considered so far, since they are based on the inter-actions between the magnetic moments. These effects belong there-fore to the class of co-operative phenomena. The theory of ferromag-netism (antiFerromagnetism, ferrimagnetism) can be subdivided into two parts. On the one hand, we have the subject of spontaneous mag-netisation (saturation magnetisation), where the very nature of ferro-magnetism is the object of consideration. The second part comprises all effects caused by the magnetic anisotropy of the crystals: for exam-ple, the theory of the technical magnetisation curve, which deals with the adjustment of the individual uniformly magnetised domains in an external field and thus the problems of hysteresis, the theory of domain structure, the Bloch walls representing the transition region between two domains, and magnetostriction. This part, which is im-portant for applications, will not be treated in this book; we refer the reader to standard books (Bates, 1961; Becker and Döring, 1939; Kneller, 1962; Bozorth, 1951; Chikazumi, 1964) and review articles (Kittel and Gait, 1957; Kanamori, 1963). First we are confronted with the problem of interactions between the atomic magnetic moments. We see at once that it cannot be de-scribed by an ordinary dipole interaction, which is of the order of μ ^Ι(^ ^ 10~^®erg,if we assume a mean distance α of about 1 A between the atoms. The Curie temperatures Γ^., however, can amount to several hundred degrees Kelvin so that a thermal energy of kT^ ^ 10^* erg is necessary to destroy the magnetically ordered state. Dipole inter-actions can therefore be at most a correction (anisotropy effect) to the real cause. Indeed, the interaction is an electrostatic one, as was first shown by Heisenberg (1928). To illustrate this, let us consider l.T.M. 11 149
eBook - PDFMaterials Science and Engineering, P-eBK
An Introduction
- William D. Callister, Jr., David G. Rethwisch, Aaron Blicblau, Kiara Bruggeman, Michael Cortie, John Long, Judy Hart, Ross Marceau, Ryan Mitchell, Reza Parvizi, David Rubin De Celis Leal, Steven Babaniaris, Subrat Das, Thomas Dorin, Ajay Mahato, Julius Orwa(Authors)
- 2020(Publication Date)
- Wiley(Publisher)
H = 0 Permanent magnetic moments in ferromagnetic materials result from atomic magnetic moments due to uncancelled electron spins as a consequence of the electron structure. 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 mag- netic moments of adjacent atoms to align with one another, even in the absence of an external field. This is schematically illustrated in figure 20.7. 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. The maximum possible magnetisation, or saturation magnetisation, M s , of a ferromagnetic material represents the magnetisation 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 magnetisation 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. 20.5 AntiFerromagnetism and ferrimagnetism AntiFerromagnetism Magnetic moment coupling between adjacent atoms or ions also occurs in materials other than those that are ferromagnetic. In one such group, this coupling results in an antiparallel alignment; the alignment of the spin moments of neighbouring atoms or ions in exactly opposite directions is termed antiFerromagnetism. Manganese oxide (MnO) is one material that displays this behaviour. Manganese oxide is a ceramic material that is ionic in character, having both Mn 2+ and O 2− ions. No net magnetic moment is associated with the O 2− ions because there is a total cancellation of both spin and orbital moments.
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