Technology & Engineering
Diamagnetism
Diamagnetism is a property of materials that causes them to create a weak magnetic field in opposition to an applied magnetic field. This results in the material being repelled by the magnetic field. Diamagnetic materials include most substances, such as water, wood, and living tissue, and exhibit this property in the absence of an external magnetic field.
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11 Key excerpts on "Diamagnetism"
No longer available |Learn more- (Author)
- 2014(Publication Date)
- Academic Studio(Publisher)
____________________ WORLD TECHNOLOGIES ____________________ Chapter- 12 Diamagnetism and Paramagnetism Diamagnetism Levitating pyrolytic carbon ____________________ WORLD TECHNOLOGIES ____________________ Diamagnetism is the property of an object which causes it to create a magnetic field in opposition to an externally applied magnetic field, thus causing a repulsive effect. Specifically, an external magnetic field alters the orbital velocity of electrons around their nuclei, thus changing the magnetic dipole moment. According to Lenz's law, this opposes the external field. Diamagnets are materials with a magnetic permeability less than μ 0 (a relative permeability less than 1). Consequently, Diamagnetism is a form of magnetism that is only exhibited by a substance in the presence of an externally applied magnetic field. It is generally quite a weak effect in most materials, although superconductors exhibit a strong effect. Diamagnetic materials cause lines of magnetic flux to curve away from the material, and superconductors can exclude them completely (except for a very thin layer at the surface). History In 1778 S. J. Bergman was the first individual to observe that bismuth and antimony were repelled by magnetic fields. However, the term Diamagnetism was coined by Michael Faraday in September 1845, when he realized that all materials in nature possessed some form of diamagnetic response to an applied magnetic field. Diamagnetic materials Notable diamagnetic materials Material (SI units) Bismuth -16.6 Carbon (diamond) -2.1 Carbon (graphite) -1.6 Copper -1.0 Lead -1.8 ____________________ WORLD TECHNOLOGIES ____________________ Mercury -2.9 Silver -2.6 Water -0.91 Superconductor -10 5 Diamagnetism is a very general phenomenon, because all electrons, including the electrons of an atom, will always make a weak contribution to the material's response.
No longer available |Learn more- (Author)
- 2014(Publication Date)
- Learning Press(Publisher)
____________________ WORLD TECHNOLOGIES ____________________ Chapter- 3 Diamagnetism and Paramagnetism Diamagnetism Levitating pyrolytic carbon ____________________ WORLD TECHNOLOGIES ____________________ Diamagnetism is the property of an object which causes it to create a magnetic field in opposition to an externally applied magnetic field, thus causing a repulsive effect. Specifically, an external magnetic field alters the orbital velocity of electrons around their nuclei, thus changing the magnetic dipole moment. According to Lenz's law, this opposes the external field. Diamagnets are materials with a magnetic permeability less than μ 0 (a relative permeability less than 1). Consequently, Diamagnetism is a form of magnetism that is only exhibited by a substance in the presence of an externally applied magnetic field. It is generally quite a weak effect in most materials, although superconductors exhibit a strong effect. Diamagnetic materials cause lines of magnetic flux to curve away from the material, and superconductors can exclude them completely (except for a very thin layer at the surface). History In 1778 S. J. Bergman was the first individual to observe that bismuth and antimony were repelled by magnetic fields. However, the term Diamagnetism was coined by Michael Faraday in September 1845, when he realized that all materials in nature possessed some form of diamagnetic response to an applied magnetic field. Diamagnetic materials Notable diamagnetic materials Material (SI units) Bismuth -16.6 Carbon (diamond) -2.1 Carbon (graphite) -1.6 ____________________ WORLD TECHNOLOGIES ____________________ Copper -1.0 Lead -1.8 Mercury -2.9 Silver -2.6 Water -0.91 Superconductor -10 5 Diamagnetism is a very general phenomenon, because all electrons, including the electrons of an atom, will always make a weak contribution to the material's response.
eBook - PDFFundamentals of Materials Science and Engineering
An Integrated Approach
- William D. Callister, Jr., David G. Rethwisch(Authors)
- 2021(Publication Date)
- Wiley(Publisher)
Bohr magneton 18.3 Diamagnetism AND PARAMAGNETISM Diamagnetism is a very weak form of magnetism that is nonpermanent and persists only while an external field is being applied. It is induced by a change in the orbital motion of electrons due to an applied magnetic field. The magnitude of the induced magnetic mo- ment is extremely small and in a direction opposite to that of the applied field. Thus, the relative permeability μ r is less than unity (however, only very slightly), and the magnetic susceptibility is negative—that is, the magnitude of the B field within a diamagnetic solid is less than that in a vacuum. The volume susceptibility χ m for diamagnetic solid materials is on the order of −10 −5 . When placed between the poles of a strong electro- magnet, diamagnetic materials are attracted toward regions where the field is weak. Figure 18.5a illustrates schematically the atomic magnetic dipole configurations for a diamagnetic material with and without an external field; here, the arrows represent atomic dipole moments, whereas for the preceding discussion, arrows denoted only elec- tron moments. The dependence of B on the external field H for a material that exhibits diamagnetic behavior is presented in Figure 18.6. Table 18.2 gives the susceptibilities of several diamagnetic materials. Diamagnetism is found in all materials, but because it is so weak, it can be observed only when other types of magnetism are totally absent. There are very few practical applications for this form of magnetism. For some solid materials, each atom possesses a permanent dipole moment by virtue of incomplete cancellation of electron spin and/or orbital magnetic moments. In the absence of an external magnetic field, the orientations of these atomic magnetic moments are random, such that a piece of material possesses no net macroscopic mag- netization.
eBook - PDFFundamentals of Materials Science and Engineering
An Integrated Approach
- William D. Callister, Jr., David G. Rethwisch(Authors)
- 2022(Publication Date)
- Wiley(Publisher)
For an atom having completely filled electron shells or subshells, when all electrons are considered, there is total cancellation of both orbital and spin moments. Thus, materi- als composed of atoms having completely filled electron shells are not capable of being permanently magnetized. This category includes the inert gases (He, Ne, Ar, etc.), as well as some ionic materials. The types of magnetism include Diamagnetism, paramag- netism, and ferromagnetism; in addition, antiferromagnetism and ferrimagnetism are considered to be subclasses of ferromagnetism. All materials exhibit at least one of these types, and the behavior depends on the response of electron and atomic magnetic dipoles to the application of an externally applied magnetic field. Bohr magneton 18.3 | | Diamagnetism AND PARAMAGNETISM Diamagnetism is a very weak form of magnetism that is nonpermanent and persists only while an external field is being applied. It is induced by a change in the orbital motion of electrons due to an applied magnetic field. The magnitude of the induced magnetic mo- ment is extremely small and in a direction opposite to that of the applied field. Thus, the relative permeability μ r is less than unity (however, only very slightly), and the magnetic susceptibility is negative—that is, the magnitude of the B field within a diamagnetic solid is less than that in a vacuum. The volume susceptibility χ m for diamagnetic solid materials is on the order of −10 −5 . When placed between the poles of a strong electro- magnet, diamagnetic materials are attracted toward regions where the field is weak. Figure 18.5a illustrates schematically the atomic magnetic dipole configurations for a diamagnetic material with and without an external field; here, the arrows represent atomic dipole moments, whereas for the preceding discussion, arrows denoted only elec- tron moments.
- William D. Callister, Jr., David G. Rethwisch(Authors)
- 2020(Publication Date)
- Wiley(Publisher)
For an atom having completely filled electron shells or subshells, when all electrons are considered, there is total cancellation of both orbital and spin moments. Thus, materials composed of atoms having completely filled electron shells are not capable of being per- manently magnetized. This category includes the inert gases (He, Ne, Ar, etc.) as well as some ionic materials. The types of magnetism include Diamagnetism, paramagnetism, and ferromagnetism; in addition, antiferromagnetism and ferrimagnetism are consid- ered to be subclasses of ferromagnetism. All materials exhibit at least one of these types, and the behavior depends on the response of electron and atomic magnetic dipoles to the application of an externally applied magnetic field. Bohr magneton Diamagnetism is a very weak form of magnetism that is nonpermanent and persists only while an external field is being applied. It is induced by a change in the orbital motion of electrons due to an applied magnetic field. The magnitude of the induced magnetic mo- ment is extremely small and in a direction opposite to that of the applied field. Thus, the relative permeability r is less than unity (however, only very slightly), and the magnetic susceptibility is negative—that is, the magnitude of the B field within a diamagnetic solid is less than that in a vacuum. The volume susceptibility m for diamagnetic solid materi- als is on the order of −10 −5 . When placed between the poles of a strong electromagnet, diamagnetic materials are attracted toward regions where the field is weak. Figure 20.5a illustrates schematically the atomic magnetic dipole configurations for a diamagnetic material with and without an external field; here, the arrows represent atomic dipole moments, whereas for the preceding discussion, arrows denoted only elec- tron moments. The dependence of B on the external field H for a material that exhibits diamagnetic behavior is presented in Figure 20.6.
eBook - PDFMaterials Science and Engineering
An Introduction
- William D. Callister, Jr., David G. Rethwisch(Authors)
- 2018(Publication Date)
- Wiley(Publisher)
For an atom having completely filled electron shells or subshells, when all electrons are considered, there is total cancellation of both orbital and spin moments. Thus, materials composed of atoms having completely filled electron shells are not capable of being per- manently magnetized. This category includes the inert gases (He, Ne, Ar, etc.) as well as some ionic materials. The types of magnetism include Diamagnetism, paramagnetism, and ferromagnetism; in addition, antiferromagnetism and ferrimagnetism are consid- ered to be subclasses of ferromagnetism. All materials exhibit at least one of these types, and the behavior depends on the response of electron and atomic magnetic dipoles to the application of an externally applied magnetic field. Bohr magneton Diamagnetism is a very weak form of magnetism that is nonpermanent and persists only while an external field is being applied. It is induced by a change in the orbital motion of electrons due to an applied magnetic field. The magnitude of the induced magnetic mo- ment is extremely small and in a direction opposite to that of the applied field. Thus, the relative permeability r is less than unity (however, only very slightly), and the magnetic susceptibility is negative—that is, the magnitude of the B field within a diamagnetic solid is less than that in a vacuum. The volume susceptibility m for diamagnetic solid materi- als is on the order of −10 −5 . When placed between the poles of a strong electromagnet, diamagnetic materials are attracted toward regions where the field is weak. Figure 20.5a illustrates schematically the atomic magnetic dipole configurations for a diamagnetic material with and without an external field; here, the arrows represent atomic dipole moments, whereas for the preceding discussion, arrows denoted only elec- tron moments. The dependence of B on the external field H for a material that exhibits diamagnetic behavior is presented in Figure 20.6.
eBook - PDFFundamentals of Materials Science and Engineering
An Integrated Approach
- William D. Callister, Jr., David G. Rethwisch(Authors)
- 2016(Publication Date)
- Wiley(Publisher)
For an atom having completely filled electron shells or subshells, when all electrons are considered, there is total cancellation of both orbital and spin moments. Thus, materi- als composed of atoms having completely filled electron shells are not capable of being permanently magnetized. This category includes the inert gases (He, Ne, Ar, etc.), as well as some ionic materials. The types of magnetism include Diamagnetism, paramag- netism, and ferromagnetism; in addition, antiferromagnetism and ferrimagnetism are considered to be subclasses of ferromagnetism. All materials exhibit at least one of these types, and the behavior depends on the response of electron and atomic magnetic dipoles to the application of an externally applied magnetic field. Bohr magneton 18.3 Diamagnetism AND PARAMAGNETISM Diamagnetism is a very weak form of magnetism that is nonpermanent and persists only while an external field is being applied. It is induced by a change in the orbital motion of electrons due to an applied magnetic field. The magnitude of the induced magnetic mo- ment is extremely small and in a direction opposite to that of the applied field. Thus, the relative permeability r is less than unity (however, only very slightly), and the magnetic susceptibility is negative—that is, the magnitude of the B field within a diamagnetic solid is less than that in a vacuum. The volume susceptibility χ m for diamagnetic solid materials is on the order of −10 −5 . When placed between the poles of a strong electro- magnet, diamagnetic materials are attracted toward regions where the field is weak. Figure 18.5a illustrates schematically the atomic magnetic dipole configurations for a diamagnetic material with and without an external field; here, the arrows represent atomic dipole moments, whereas for the preceding discussion, arrows denoted only elec- tron moments. The dependence of B on the external field H for a material that exhibits diamagnetic behavior is presented in Figure 18.6.
eBook - PDF- Wenceslao González-Viñas, Héctor L. Mancini(Authors)
- 2015(Publication Date)
- Princeton University Press(Publisher)
Diamagnetism can be understood with the help of the Lenz law. If an atom has the same number of electrons moving in both directions, and if there is an equal number of electrons with spin up and down, then the global permanent magnetic moment is zero. This will happen in molecules with closed shells of electrons. It leads to a zero net angular momentum, as occurs in Bi, Be, Ag, Au, Ge, Cu, Si, MgO, and so forth. If we apply a magnetic field, the internal currents change and the changes are opposite to the variations of the magnetic flux. This creates a net field—and hence we measure a net magnetic moment—opposite to the applied one. As a consequence, the material repels magnets. All these behaviors occur in both directions of movement without canceling themselves, and so magnetic dipoles are induced. If the material is paramagnetic, the field’s first effect is to orient the permanent magnetic dipoles in the field direction. After that, the diamagnetic component appears, but is much smaller than the paramagnetic one (of the order of µ B ). Hence, Diamagnetism is relevant only at high temperatures where paramagnetism responds to the disordering effect of thermal vibration. A superconductor, as we see in chapter 7, is a perfect diamagnet. Its magnetic suscepti- bility is, then, χ = −1. 60 CHAPTER 6 To guess the diamagnetic magnetization it is necessary to realize that, when a magnetic field B is applied, the force changes in such a way that it equals the centripetal force evB = dF = 2mvdv/r . Therefore, dv = erB/2m e . The magnetic moment of a moving charge is µ = (1/2)evr ; consequently, the change of magnetic moment will be µ = 1 2 erdv = e 2 r 2 B 4m e ∼ 10 −5 µ B , as we predicted. 6.2 FERROMAGNETISM, FERRIMAGNETISM, AND ANTIFERROMAGNETISM Ferromagnetic materials (Fe, Co, Ni, their alloys, Gd, Dy, etc.) have large positive values of the magnetic susceptibility that depend on the magnetic field.
eBook - PDF- Sharon Ann Holgate(Author)
- 2009(Publication Date)
- CRC Press(Publisher)
It is only possible to levitate diamagnetic objects, and although every substance on earth shows some diamagnetic response to a magnetic field, only living organisms, wood, plastics, and other substances that would not normally be considered as magnetic are diamagnetic overall. This is because Diamagnetism is so weak that it is masked by stronger forms of magnetism. If a diamagnetic substance is placed in a magnetic field, the electrons of every atom of the substance change their orbits slightly and produce a weak magnetic field that opposes the external field. So diamagnetic substances and strong magnetic fields repel each other. If a diamagnetic object like a water droplet or a frog is placed in a large magnetic field—such as the 10 tesla field within the bore of the magnet shown here—it becomes a small magnet that generates a magnetic field of about 1 gauss. (This is roughly the same strength as the Earth’s magnetic field.) The force of repulsion between the 10 tesla and 1 × 10 −4 tesla magnets pushes the diamag-netic object upwards and compensates the force of gravity that would normally cause it to fall to the ground, so the object levitates. In principle, anything diamagnetic, including a human being, could be levitated in this way if the magnetic field was strong enough. (Images courtesy of Andrey Geim.) 276 Understanding Solid State Physics Atomic Paramagnetism We saw in Section 8.1.1 that the total magnetic moment of an atom is made up from all the orbital and spin magnetic moments of the individual electrons that have not cancelled each other out. When there is no external magnetic field, the magnetic moments of the atoms in paramagnetic materials are randomly orientated so that there is no overall magnetic moment from them. However, with a field applied, this situation changes and a net magnetisation is produced, as the individual magnetic moments partially line up with the external field, as shown in Figure 8.2.
- Robert J. Naumann(Author)
- 2008(Publication Date)
- CRC Press(Publisher)
Probably the easiest way to understand Diamagnetism is to consider the effect of an applied magnetic fi eld on the orbit of an electron. Consider an electron orbiting a nucleus with angular velocity v 0 at radius r 0 . From Equation 25.6, the magnetic moment will be m M ¼ qr 2 v 0 = 2 where v 0 is the unperturbed orbital frequency in the right-hand sense. The Coulomb force on the electron is mr v 0 2 . In the presence of a magnetic fi eld, the electron will feel a Lorentz force q ( n B ) ¼ qr v B if the B is aligned with m M . The effect of the magnetic fi eld is to oppose the Coulomb attraction, thus slowing the v of the electron which reduces its 496 Introduction to the Physics and Chemistry of Materials magnetic moment (this is a consequence of Lenz ’ s law which states that the current induced by a magnetic fi eld creates an opposing fi eld). Quantitatively, the new angular frequency is v 2 ¼ v 2 0 qB m v : (25 : 12) Solving for v v ¼ v 0 qB 2 m þ O B 2 : (25 : 13) The new magnetic moment is m 0 M ¼ qr 2 2 v 0 qB 2 m ¼ m M q 2 r 2 4 m B : (25 : 14) Had the B -fi eld been opposite the m M , the effect would be to speed up the electron and make the magnetic moment more negative and Equation 25.14 would be m 0 M ¼ qr 2 2 v 0 þ qB 2 m ¼ m M q 2 r 2 4 m B : (25 : 15) If we sum over Z electrons per atom and N atoms = m 3 , the m M cancel out and the magnetic susceptibility becomes x ¼ M H ¼ m 0 ZN D m m B ¼ m 0 ZNq 2 r 2 4 m : (25 : 16) Since the susceptibility < 0, the response is diamagnetic. We estimate the susceptibility by taking Z ¼ 10, N ¼ 10 28 m 3 , r ¼ 10 10 m, m ¼ 10 30 kg, and m 0 ¼ 10 6 , q 10 19 , x 10 5 . 25.3.2 Larmor Diamagnetism (Quantum Approach) Quantum mechanics does not allow the orbital angular momentum to line up with the magnetic fi eld as assumed in the previous example. Instead L projects a component, hm ‘ on the B -direction as was shown in Chapter 2. A magnetic fi eld exerts a torque on a magnetic moment according to _ L ¼ m M B .
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)
(c ) The inside of a hard disk drive. The circular disk will typically spin at a rotational velocity of 5400 or 7200 revolutions per minute. (d ) A laptop computer; one of its internal components is a hard disk drive. 20.1 Introduction 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, telephones, 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; dia- magnetism, paramagnetism, ferromagnetism, and ferrimagnetism; different magnetic materials; and superconductivity. 20.2 Basic concepts Magnetic dipoles FIGURE 20.1 Magnetic field lines of force around a current loop and a bar magnet. N S Magnetic forces are generated by moving electrically charged particles; these magnetic forces are in addi- tion 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 20.1.
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