Technology & Engineering
Ferrimagnetic Materials
Ferrimagnetic materials are a type of magnetic material characterized by two different sublattices with opposing magnetic moments. These materials exhibit a net magnetization due to the unequal alignment of the magnetic moments within the sublattices. They are commonly used in applications such as magnetic recording media, microwave devices, and magnetic sensors due to their unique magnetic properties.
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12 Key excerpts on "Ferrimagnetic Materials"
- Donald Askeland, Wendelin Wright, Donald Askeland(Authors)
- 2020(Publication Date)
- Cengage Learning EMEA(Publisher)
The term “nonmagnetic,” usually means that the material is neither ferromagnetic nor ferrimagnetic. These “nonmagnetic” materials are further classified as diamagnetic (e.g., superconductors) or paramagnetic. In some cases, we also encounter materials that are antiferromagnetic or superparamagnetic. We will discuss these different classes of materials and their applica- tions later in the chapter. Ferromagnetic and Ferrimagnetic Materials are usually further classified as either soft or hard magnetic materials. High-purity iron or plain carbon steels are examples of a magnetically soft material as they can become magnetized, but when the magnetizing source is removed, these materials lose their magnet-like behavior. Permanent magnets or hard magnetic materials retain their magnetization. These are permanent “magnets.” Many ceramic ferrites are used to make inexpensive refrigera- tor magnets. A hard magnetic material does not lose its magnetic behavior easily. 20-2 Magnetic Dipoles and Magnetic Moments The magnetic behavior of materials can be traced to the structure of atoms. The orbital motion of the electron around the nucleus and the spin of the electron about its own axis (Figure 20-1) cause separate magnetic moments. These two motions (i.e., spin and orbital) contribute to the magnetic behavior of materials. When the electron spins, there is a mag- netic moment associated with that motion. The magnetic moment of an electron due to its spin is known as the Bohr magneton (m B ). This is a fundamental constant and is defined as B 5 Bohr magneton 5 q h 4m e 5 9.274 3 10 224 A? m 2 (20-1) Figure 20-1 Origin of magnetic dipoles: (a) The spin of the electron produces a mag- netic field with a direction dependent on the quantum number m s . (b) Electrons orbiting around the nucleus create a magnetic field around the atom. Copyright 2022 Cengage Learning. All Rights Reserved. May not be copied, scanned, or duplicated, in whole or in part.
eBook - PDF- Bozzano G Luisa(Author)
- 2013(Publication Date)
- Academic Press(Publisher)
13 Ferrimagnetic Electron Devices 13.1 Ferrimagnetic Materials Ferrimagnetic Materials provide important parts in various mi-crowave electronic systems [1]. Ferrimagnetic Materials are used in tuners, filters, attenuators, isolators, circulators, modulators, switches, and shutters. In this chapter, practical aspects and basic theory of the interaction of Ferrimagnetic Materials with mi-crowaves are studied, and principles of practical ferrimagnetic microwave circuit components are investigated. Common Ferrimagnetic Materials used for microwave applica-tions are ferrites and garnets. When ferrites and garnets are dc magnetized and the microwave magnetic field h is applied perpen-dicularly to the magnetizing dc magnetic field, the induced mi-crowave flux density b is not parallel to the magnetic field h. On the other hand, for ferromagnetic material, the microwave mag-netic field h and microwave magnetic flux density b are parallel to each other whether the material is magnetized or not. In the magnetized ferrimagnetic material, the microwave magnetic field h and microwave magnetic flux density b are not parallel to each other. In the soft ferrite, if the magnetizing dc magnetic field is removed and no residual magnetism exists, it then turns into pseudo-ferromagnetic material, or the microwave magnetic flux density b becomes parallel to microwave magnetic fields h [2]. It is 241 2 4 2 Ferrimagnetic Electron Devices interesting to investigate why b is not parallel to h in dc magne-tized ferrimagnetic material. 13.2 Gyromagnetic Equations The ferrimagnetic phenomenon is due to the precessing magnetic dipole moment of bound unpaired electrons in the ferrite material. For example, if the ferrite is Fe 3 0 4 , it contains unpaired electrons in F e 3 + ions. These unpaired spinning electrons are responsive to applied magnetic fields, both dc and microwave. Since electrons are negatively charged, if they are spinning they can be considered tiny magnets.
eBook - PDF- Pradeep Fulay, Jung-Kun Lee(Authors)
- 2016(Publication Date)
- CRC Press(Publisher)
Therefore, a material such as iron has a net magnetic moment. In iron, all the magnetic moments of the atoms are in the same direction, due to an exchange interac-tion between neighboring spin magnetic moments. A material in which all the magnetic moments of atoms or ions are aligned in the same direction is known as a ferromagnetic material . It possesses strong net magnetic moments without an external magnetic field. (Figure 11.3). TABLE 11.1 Pairing of 3d and 4s Electrons in Different Transition Elements Element Atomic Number (Z) 3d-Electron Spin Pairing 4s-Electron Spin Pairing Sc 21 ↑ ↑↓ Ti 22 ↑ ↑ ↑↓ V 23 ↑ ↑ ↑ ↑↓ Cr 24 ↑ ↑ ↑ ↑ ↑ ↑ Mn 25 ↑ ↑ ↑ ↑ ↑ ↑↓ Fe 26 ↑↓ ↑ ↑ ↑ ↑ ↑↓ Co 27 ↑↓ ↑↓ ↑ ↑ ↑ ↑↓ Ni 28 ↑↓ ↑↓ ↑ ↑ ↑ ↑↓ Cu 29 ↑↓ ↑↓ ↑↓ ↑↓ ↑↓ ↑ 477 Magnetic Materials In some materials (e.g., iron oxide [Fe 3 O 4 ]), the ions at the different locations of the unit cell have magnetic moments that are aligned in opposite directions or are antiparallel. However, the magnetic moments of two sublattices are not completely canceled out, because two sublattices do not have the same magnitude of the magnetic moments (see Example 11.2). A material in which the magnetic moments of atoms or ions are antiparallel but are not canceled out is known as a ferrimagnetic mate-rial . The alignment of electron spins in Ferrimagnetic Materials is shown schematically in Figure 11.3. Note that ferromagnetic or Ferrimagnetic Materials do not have to contain iron or other ferromagnetic elements (e.g., Ni, Co, Gd). For example, Cu 2 MnAl, ZrZn, and InSb are ferromag-netic, even though the latter two are ferromagnetic only at very low temperatures (O’Handley 1999). If the spin magnetic moments due to different ions or atoms are completely canceled out, the material is known as antiferromagnetic (e.g., Cr, α -Mn, and MnO).
eBook - PDFMicrowave Engineering
Concepts and Fundamentals
- Ahmad Shahid Khan(Author)
- 2014(Publication Date)
- CRC Press(Publisher)
In ferromagnetic substances, the electrons are close enough to reinforce the effect of each other and the resulting magnetic field is much stronger. Thus, ferromagnetic materials have fairly large magnetic permeabilities. Unfortunately, conductivities of these materials are also fairly high. The application of high-frequency mag-netic fields to such materials results in large eddy currents and hence, in significant power loss. 164 Microwave Engineering TABLE 5.1 Magnetic Materials, Magnetic Moments and Relative Values of Flux Densities No. Material Magnetic Moments Value of B Remarks 1 Diamagnetic m orb + m spin = 0 B int < B app B int and B app are almost equal 2 Paramagnetic m orb + m spin ⇒ 0 B int > B app B int and B app are almost equal 3 Ferromagnetic | m spin | >> | m orb | B int >> B app Contains the domain, adjacent domains align and add to the result in large internal flux density 4 Anti-ferromagnetic | m spin | >> | m orb | B int ≈ B app Contains the domain, equal adjacent domains oppose, result in total cancellation and no enhancement in internal flux density 5 Ferrimagnetic | m spin | > | m orb | B int > B app Contains domains, unequal adjacent domains oppose, no total cancellation and enhancement in internal flux density 6 Super paramagnetic | m spin | >> | m orb | B int > B app Contains the matrix of magnetic and non-magnetic materials Weak magnetic field Domains (a) (b) Dipoles Domains Dipoles Strong magnetic field FIGURE 5.2 (a) Unmagnetised and (b) magnetised material. Orbit of revolving electron Nucleus of atom Spin axis Spinning electron FIGURE 5.1 Revolving and spinning electrons. 165 Microwave Ferrite Devices 5.2 Ferrites The nature of alignments in different materials is shown in Figure 5.3. In the case of ferromagnetic materials, these dipoles align in the same direction in different domains and thus aid in the creation of a strong magnetic field.
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.
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.
- David Jiles(Author)
- 2015(Publication Date)
- CRC Press(Publisher)
, 51, 5907, 2003. Littmann, M. F. IEEE Trans. Mag ., 7, 48, 1971. Schneider, J., Stoecker, A., Franke, F., Schroeder, C., Li, G., and Hermann, H., Evolution of microstructure and texture along the processing route of ferritic non-oriented FeSi steels, in Proceedings of the 6th International Conference on Magnetism and Metallurgy , Cardiff, June 17–19, 2014. MATERIALS Soft Magnetic Materials. http://www.softmagneticalloy.com/soft_magnetic_materials.htm. Grain Oriented Electrical Steels. http://www.cogent-power.com/grain-oriented/. 357 Soft Magnetic Materials CONFERENCES Soft Magnetic Materials Conference. http://en.wikipedia.org/wiki/Soft_Magnetic_Materials_ Conference. International Magnetics Conference. http://www.intermagconference.com/. Magnetism and Magnetic Materials Conference. http://www.magnetism.org/. This page intentionally left blank This page intentionally left blank 359 13 Hard Magnetic Materials In this chapter, we consider the properties of ferromagnets that make them useful as permanent magnets. A range of different permanent materials is available, many of which include rare earth metals, but there has been increasing interest in recent years to develop better rare-earth free permanent magnets. Improvements in properties such as increased coercivity, remanence, and maximum energy product continue to be made. The control of magnetic properties through alteration of the nanostructure is central to the development of improved permanent magnets as in hot deformed neodymium-iron-boron permanent magnets and two-phase exchange spring magnets. However, in addition to the materials properties, the shape of the permanent magnets is important in providing the desired flux density at a given loca-tion, so demagnetizing effects resulting from a combination of magnetization and shape need to be considered. 13.1 PROPERTIES AND APPLICATIONS OF HARD MAGNETS A permanent magnet is a passive device used for generating a magnetic field.
- Wei Gao, Zhengwei Li;Nigel Sammes;;(Authors)
- 2011(Publication Date)
- WSPC(Publisher)
Magnetic Properties and Materials 159 make magnets was to rub steel with a lodestone or another magnet, until the electromagnetic field was discovered by Hans Oersted in ~1820. It was not generally recognised that the development of new magnetic materials was also responsible for the revolutionary developments in modern electric and electronic industries. Magnetic materials play very important roles in almost all the equipment that use modern technology, for example, ferrite magnets in TV, memory cores in computers, permanent magnets in motors, superconducting magnets in particle accelerators, to name a few. We would have no audio/video equipment without suitable magnetic materials. Magnetic materials are functional materials, but sometimes they are also used in large quantities (many tons) such as for the core materials in power transformers. Like semiconductor materials, the quality of mag-netic materials strongly influences the performance, efficiency, energy consumption, size and reliability of electric and electronic equipment. Great progress has been made in quality improvement of the magnetic materials in the recent years. Fig. 6.1 shows the progress in permanent magnetic materials during the last 100 years. Fig. 6.1 Progress in magnetic materials measured by the maximum energy products ( BH ) max . Year 1900 1980 1940 1960 2000 1920 100 300 400 200 500 (BH) max (kJ/m 3 ) Steel Alnico SmCo 5 SmCo 7.5 Nd -Fe -B 160 Introduction to Electronic Materials for Engineers 6.2 Fundamentals 6.2.1 Magnetic flux and permeability Compare an electric circuit with a magnetic circuit (Fig. 6.2): if a volt-age, V , is applied to a conductor, the current I that flows in it is related to the conductivity σ of the material: Fig. 6.2 Analogy between (a) electric circuit and (b) magnetic circuit. V = I · R, R = ρ ⋅ l/A = l/ ( σ ⋅ A ), V = ( I/A )( l/ σ ), σ = ( I/A ) × ( 1/E ), (6.1) E = V/l, σ = J/E = (current density)/(electrical field).
eBook - PDF- G R Jones(Author)
- 2013(Publication Date)
- Newnes(Publisher)
Whole areas may be screened with iron enclosures where steady field or field-free conditions are essential. For this purpose screens consisting of layers of iron and air are the most effective. 14.4 Ferrites In the present context, ferrites may be defined as magnetic materials consisting of compounds of metal oxides and con-taining ferric ions as the main constituent. They generally have the form of polycrystalline ceramic materials, although for some special applications the single-crystal form is used. Ferrites are used in a wide variety of applications in electronic and communication engineering. In the crystal lattice of ferrites the metal ions are separated by oxygen ions and this results in high electrical resistivities which suppress the effects of eddy currents. The presence of oxygen ions also results in the magnetic moments of the metal ions on the constituent sublattices having anti-parallel align-ment so that the net available magnetisation is the difference between the magnetisations of the sublattices. This, together with the dilution due to the non-magnetic oxygen ions, inherently limits the saturation flux density to about 0.4-0.6 T (compared with about 2 T for some magnetic alloys). The usual manufacturing process consists of the following steps: mixing of raw materials (oxides, carbonates, etc.) in the required proportions; calcining at about 1000°C; crushing; milling; powder granulation; forming to the required shape by pressing the powder in a die or by extrusion; and, finally, sintering the piece parts at about 1250°C for up to 12 h in a controlled atmosphere. During sintering, crystallites of the required formulation are created by solid-state reaction and this is accompanied by a shrinkage of linear dimensions of between 10 and 25%. The product is a black brittle ceramic component having a density of about 4800 kg/m 3 . Any subse-quent shaping operations, such as pole-face finishing, have to be done by grinding (and sometimes lapping).
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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