Technology & Engineering
Paramagnetic Materials
Paramagnetic materials are substances that are weakly attracted to magnetic fields. They contain unpaired electrons, which align with an external magnetic field, causing the material to become magnetized. However, this magnetization disappears when the external field is removed. Examples of paramagnetic materials include aluminum, platinum, and oxygen.
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10 Key excerpts on "Paramagnetic Materials"
No longer available |Learn more- (Author)
- 2014(Publication Date)
- Academic Studio(Publisher)
Paramagnetic Materials are attracted to magnetic fields and hence have a relativ e magnetic permeability of ≥1 (a positive magnetic susceptibility). The magnetic moment induced by the applied field is linear in the field strength and rather weak . It typically requires a sensitive analytical balance to detect the effect and modern measurements on Paramagnetic Materials are often conducted with a SQUID mag-netometer. ____________________ WORLD TECHNOLOGIES ____________________ Unlike ferromagnets, paramagnets do not retain any magnetization in the absence of an externally applied magnetic field, because thermal motion causes the spins to become randomly oriented without it. Thus the total magnetization will drop to zero when the applied field is removed. Even in the presence of the field there is only a small induced magnetization because only a small fraction of the spins will be oriented by the field. This fraction is proportional to the field strength and this explains the linear dependency. The attraction experienced by ferromagnets is non-linear and much stronger, so that it is easily observed, for instance, in magnets on one's refrigerator. Relation to electron spins Constituent atoms or molecules of Paramagnetic Materials have permanent magnetic moments (dipoles), even in the absence of an applied field. This generally occurs due to the spin of unpaired electrons in the atomic/molecular electron orbitals. In pure paramagnetism, the dipoles do not interact with one another and are randomly oriented in the absence of an external field due to thermal agitation, resulting in zero net magnetic moment. When a magnetic field is applied, the dipoles will tend to align with the applied field, resulting in a net magnetic moment in the direction of the applied field.
eBook - PDF- Pradeep Fulay, Jung-Kun Lee(Authors)
- 2016(Publication Date)
- CRC Press(Publisher)
487 Magnetic Materials 11.4.2 P ARAMAGNETIC M ATERIALS When a paramagnetic material is placed inside the coil, the flux density inside ( B int ) is slightly larger than B 0 . This effect originates from the atoms or ions that have unpaired electrons, and it leads to a net magnetic moment for the free atom or an ion. The atoms or ions are known as paramagnetic atoms or paramagnetic ions. Examples include materials such as aluminum. The atoms in these materials have a permanent magnetic moment. When a magnetic field is applied, these magnetic moments get oriented and create a magnetization in the same direction as the applied field. Thus, in Paramagnetic Materials, the susceptibility is very small ( χ m ~ + 10 −6 – 10 −3 ) but positive. As temperature increases, the thermal motion becomes important and the susceptibility of the Paramagnetic Materials decreases. This can be shown by a demonstration in which a stream of liquid oxygen is deflected by a strong permanent magnet held next to it (Featonby 2005). As a side note, the unpaired electrons that create a magnetic moment in oxygen are also related to the absorption of red light (~630-nm wavelength) and impart a blue color to liquid oxygen! Paramagnetic Materials show a slight attraction in the presence of a permanent magnet. However, the paramagnetic response is so small that, for all practical purposes, these materials are also considered nonmagnetic. Another important point is that at the Curie tempera-ture, ferromagnetic and ferrimagnetic materials transform into Paramagnetic Materials. The relative value and sign of magnetic susceptibility ( χ m ) or magnetic permeability ( μ ) are often used to classify magnetic materials. The relationships between magnetic field and magnetization for different materials are shown in Figure 11.9. Note that this diagram is not to scale. Also, it does not show the nonlinear nature of ferromagnetic and ferrimagnetic materials.
eBook - PDF- Md Nazoor Khan, Simanchala Panigrahi(Authors)
- 2017(Publication Date)
- Cambridge University Press(Publisher)
Magnetic Properties of Materials 131 Example 5.6 A magnetic field of induction B = 2.0 Wb/m 2 is applied perpendicularly to the plane of the electron’s path of radius 5.1 × 10 –11 m. Calculate the change in magnetic moment of a circulating electron. Solution The data given are B = 2.0 Wb/m 2 and < ρ 2 > = (5.1 × 10 –11 m) 2 The change in magnetic moment of a circulating electron according to Eq. (5.16) is given by ( ) ρ − − − − × × × = − < > = − × × = ± × × × 2 38 2 2 11 29 2 31 1 2.56 10 2 5.1 10 3.7 10 Am 4 4 9.1 10 Ze B m The change in magnetic moment of a circulating electron due to the application of a strong magnetic field is very small! 5.7 Paramagnetism The kind of magnetism characteristic of materials weakly attracted by a strong magnet is called paramagnetism. Most elements and some compounds are paramagnetic. Strong paramagnetism is exhibited by compounds containing iron, palladium, platinum and the rare-earth elements. In such compounds, atoms of these elements have some inner electron shells that are incomplete, causing their unpaired electrons to spin like tops and orbit like satellites, thus making the atoms or molecules a permanent magnet tending to align with and hence strengthen an applied magnetic field. Strong paramagnetism decreases with rising temperature because of the de-alignment of magnetic moments produced by the greater thermally generated random motion of the atomic magnets. Weak paramagnetism, independent of temperature, is found in many metallic elements in the solid state, such as sodium and the other alkali metals, because an applied magnetic field affects the spin of some of the loosely bound conduction electrons. The value of susceptibility for Paramagnetic Materials is always positive and at room temperature is typically about 10 –5 to 10 –4 for weakly paramagnetic substances and about 10 –4 to 10 –2 for strongly paramagnetic substances.
- Donald Askeland, Wendelin Wright, Donald Askeland(Authors)
- 2020(Publication Date)
- Cengage Learning EMEA(Publisher)
Materials such as copper, silver, silicon, gold, and alumina are diamagnetic at room temperature. Superconductors are perfect diamagnets s m 521d; they lose their superconductivity at higher temperatures or in the presence of a magnetic field. In a diamagnetic material, the magnetization (M) direction is opposite to the direction of applied field (H). Paramagnetism When materials have unpaired electrons, a net magnetic moment due to electron spin is associated with each atom. When a magnetic field is applied, the dipoles align with the field, causing a positive magnetization. Because the dipoles do not interact, extremely large magnetic fields are required to align all of the dipoles. In addition, the effect is lost as soon as the magnetic field is removed. This effect, called paramagnetism, is found in metals such as aluminum, titanium, and alloys of copper. The magnetic susceptibility (x m ) of Paramagnetic Materials is positive and Figure 20-3 The effect of the core material on the flux density. The magnetic moment opposes the field in diamagnetic materials. Progressively stronger moments are present in paramagnetic, ferrimagnetic, and ferromagnetic materials for the same applied field. 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. Chapter 20 Magnetic Materials 730 lies between 10 24 and 10 25 . Ferromagnetic and ferrimagnetic materials above the Curie temperature also exhibit paramagnetic behavior. Ferromagnetism Ferromagnetic behavior is caused by the unfilled energy levels in the 3d level of iron, nickel, and cobalt.
eBook - ePubNanomaterials
Biomedical, Environmental, and Engineering Applications
- Suvardhan Kanchi, Shakeel Ahmed, Myalowenkosi I. Sabela, Chaudhery Mustansar Hussain, Suvardhan Kanchi, Shakeel Ahmed, Myalowenkosi I. Sabela, Chaudhery Mustansar Hussain(Authors)
- 2018(Publication Date)
- Wiley-Scrivener(Publisher)
Based on the magnetism basis, it shows that the magnetism lies between the spin motion of electrons and orbitals, as well as how interactions of electrons occur with one another. No aggregate magnetic interactions are shown for substances in the first two groups and are also not in a magnetic arrangement. Below distinct temperatures, substances in the last three groups display a magnetic arrangement in a long range. Some of the substances that we recognize to be magnetic (i.e., possess iron behavior) are ferrimagnetic and ferromagnetic substances [17]. The three outstanding magnetic substances are weakly in such a way that they are considered as “nonmagnetic”. Based on the magnetic performance of substances, they are categorized into the following five significant groups:- Paramagnetic Materials
- Diamagnetic materials
- Ferri magnetic materials
- Ferro magnetic materials
- Anti-ferro magnetic materials
7.1.5.1 Paramagnetic Substances
In this group of substances, some of the atoms or ions have unpaired electrons and incompletely filled orbitals. The Langevin classification, which is applicable to substances with non-interacting localized electrons, stipulates that each atom has a randomly orientated magnetic moment resulting from thermal agitation (Figure 7.4 ). Moreover, the atomic magnets experience no interaction among each other. An incomplete orientation of these atomic magnetic moments in the direction of applied magnetic field results in a net positive magnetization and positive susceptibility in the presence of a magnetic field [18]. Moreover, when the temperature of Paramagnetic Materials increases, the orientation of the atomic magnets is disturbed. This simply means that the susceptibility of the magnet is inversely proportional to the absolute temperature.Plot of M vs. H for paramagnetism.Figure 7.47.1.5.2 Diamagnetic Substances
An essential property of all material is diamagnetism, which is categorized as a weak magnetism and is in the direction opposite to that of the applied field. There is no permanent dipole moment in each atom. It is because of the non-cooperative behavior of orbiting electrons when visible to an applied magnetic field. Moreover, in diamagnetic materials, all of the atoms have paired electrons and contain no unpaired electrons in the shells. Hence, the net magnetic moment of the atom for a diamagnetic substance is zero; therefore, for all diamagnetic materials, susceptibility is negative. The additional characteristic behavior of diamagnetic substances is that their susceptibility is independent of temperature. If we plot M vs. H, we see Figure 7.5
- Wei Gao, Zhengwei Li;Nigel Sammes;;(Authors)
- 2011(Publication Date)
- WSPC(Publisher)
This effect is greater than diamagnetic effect but still very small. The magnetic suscepti-bility χ ranges from 10 -6 -10 -2 . Temperature reduces the paramagnetic ef-fects. The correlation between magnetic susceptibility and temperature can be described by Curie -Weiss law. Alkaline metals, such as Li, Na, K and Rh, can show such a weak, positive, attractive reaction to an applied field. Curie -Weiss law: χ p = C /( T - T p ), where: C : Curie constant T : Temperature T p : Paramagnetic Curie temperature. Diamagnetic and paramagnetic effects are all induced by an applied field. When field is removed, the effect disappears. Diamagnetic and paramagnetic properties have limited engineering applications. Table 6.3 Magnetic susceptibilities of some diamagnetic and Paramagnetic Materials. Diamagnetic Magnetic susceptibility ( χ × 10 -6 ) Paramagnetic Magnetic susceptibility ( χ × 10 -6 ) Cadmium -0.18 Aluminium +0.65 Copper -0.086 Calcium +1.10 Silver -0.20 Oxygen +106.2 Tin -0.25 Platinum +1.10 Zinc -0.157 Titanium +1.25 6.2.6.3 Ferromagnetism A group of materials have very different magnetisation properties from the first two groups. Firstly, the susceptibility χ is positive and very large, about 10 7 times greater than χ in Paramagnetic Materials (10 1 < χ < 10 6 ). This means that a very large magnetisation will be created by the material under an applied field. Secondly, large magnetic fields can be retained after the applied field is removed. This magnetic behaviour is called ferromagnetism, and the materials are called ferromagnetic mate-rials. These properties are of great engineering importance. Magnetic Properties and Materials 167 The most important ferromagnetic elements are Fe, Co and Ni. A ra-re-earth element gadolinium (Gd) is also ferromagnetic below 16°C, but has little engineering application. Fe, Co, and Ni are transition metals and have unpaired inner 3 d electrons (see Fig. 6.7).
eBook - PDF- Sharon Ann Holgate(Author)
- 2009(Publication Date)
- CRC Press(Publisher)
8.2.2 P ARAMAGNETISM Like diamagnetism, paramagnetism is only apparent when a magnetic field is applied, and is caused by the motion of electrons. The similarity ends there, however, as rather than being repelled, Paramagnetic Materials have a weak attraction to magnetic fields. EXAMPLE QUESTION 8.1 THE DIAMAGNETIC PROPERTIES OF SUPERCONDUCTORS What is the value of the magnetic susceptibility for a superconducting material when it is in the superconducting state? ANSWER The magnetic susceptibility, χ , is given by χ = M H where M is the magnetisation, and H is the applied magnetic field. M and H are in turn linked to the magnetic flux density B by B H M = + µ µ 0 0 where μ 0 is the permeability of free space. When a superconductor is below T C , it expels all magnetic flux from its interior, so B within it must be zero. This means we have − = ≡ = − µ µ 0 0 M H H M Combining this result with the equation for χ reveals that the magnetic suscep-tibility for a superconductor in its superconducting state is −1. By contrast, other diamagnetic materials have values of χ in the order of − x × 10 −5 (see Table 8.1). 274 Understanding Solid State Physics BOX 8.1 TOAD IN THE HOLE When scientists make discoveries, it is not often that their colleagues think their work is a hoax. But that’s exactly what happened to Prof. Andrey Geim from the University of Manchester in the U.K., whilst he was working at the University of Nijmegen in Holland in 1997. “I had come across a scientific paper which reported a rather strange phenomenon. The authors had placed a cuvette filled with water in a horizontal magnet and observed that the water level split into two walls, leaving a completely dry bottom,” recalls Prof. Geim. Intrigued by the fact there seemed to be no explanation for this effect, he poured water inside the bore (central hole) of a powerful electromagnet. “To my surprise, the water did not end up on the floor but stuck in the middle.
eBook - PDFFundamentals of Materials Science and Engineering
An Integrated Approach
- William D. Callister, Jr., David G. Rethwisch(Authors)
- 2021(Publication Date)
- Wiley(Publisher)
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. These atomic dipoles are free to rotate, and paramagnetism results when they preferentially align, by rotation, with an external field as shown in Figure 18.5b. These magnetic dipoles are acted on individually with no mutual interaction between diamagnetism paramagnetism 712 • Chapter 18 / Magnetic Properties adjacent dipoles. Inasmuch as the dipoles align with the external field, they enhance it, giving rise to a relative permeability μ r that is greater than unity and to a relatively small but positive magnetic susceptibility. Susceptibilities for Paramagnetic Materials range from about 10 −5 to 10 −2 (Table 18.2). A schematic B-versus-H curve for a paramagnetic material is shown in Figure 18.6. Both diamagnetic and Paramagnetic Materials are considered nonmagnetic because they exhibit magnetization only when in the presence of an external field. Also, for both, the flux density B within them is almost the same as it would be in a vacuum. H = 0 H H = 0 H (a) (b) Figure 18.5 (a) The atomic dipole configuration for a diamagnetic material with and without a magnetic field. In the absence of an external field, no dipoles exist; in the presence of a field, dipoles are induced that are aligned opposite to the field direction. (b) Atomic dipole configuration with and without an external magnetic field for a paramagnetic material. Flux density, B Paramagnetic Vacuum Diamagnetic 0 0 Magnetic field strength, H Figure 18.6 Schematic representation of the flux density B versus the magnetic field strength H for diamagnetic and Paramagnetic Materials.
- William D. Callister, Jr., David G. Rethwisch(Authors)
- 2020(Publication Date)
- Wiley(Publisher)
Susceptibilities for Paramagnetic Materials range from about 10 −5 to 10 −2 (Table 20.2). A schematic B-versus-H curve for a paramagnetic material is shown in Figure 20.6. Both diamagnetic and Paramagnetic Materials are considered nonmagnetic because they exhibit magnetization only when in the presence of an external field. Also, for both, the flux density B within them is almost the same as it would be in a vacuum. Figure 20.5 (a) The atomic dipole con- figuration for a diamagnetic material with and without a magnetic field. In the absence of an external field, no dipoles exist; in the presence of a field, dipoles are induced that are aligned opposite to the field direction. (b) Atomic dipole configuration with and without an external magnetic field for a paramagnetic material. H = 0 H H = 0 H (a) (b) Figure 20.6 Schematic representation of the flux density B versus the magnetic field strength H for diamagnetic and Paramagnetic Materials. Flux density, B Paramagnetic Vacuum Diamagnetic 0 0 Magnetic field strength, H Diamagnetics Paramagnetics Susceptibility Susceptibility m (volume) m (volume) Material (SI units) Material (SI units) Aluminum oxide −1.81 × 10 −5 Aluminum 2.07 × 10 −5 Copper −0.96 × 10 −5 Chromium 3.13 × 10 −4 Gold −3.44 × 10 −5 Chromium chloride 1.51 × 10 −3 Mercury −2.85 × 10 −5 Manganese sulfate 3.70 × 10 −3 Silicon −0.41 × 10 −5 Molybdenum 1.19 × 10 −4 Silver −2.38 × 10 −5 Sodium 8.48 × 10 −6 Sodium chloride −1.41 × 10 −5 Titanium 1.81 × 10 −4 Zinc −1.56 × 10 −5 Zirconium 1.09 × 10 −4 Table 20.2 Room-Temperature Magnetic Susceptibilities for Diamagnetic and Paramagnetic Materials 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).
eBook - PDFFundamentals of Materials Science and Engineering
An Integrated Approach
- William D. Callister, Jr., David G. Rethwisch(Authors)
- 2016(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. 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).
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