Physics
Magnetization
Magnetization refers to the process by which a material becomes magnetized, acquiring magnetic properties. This can occur through the alignment of magnetic domains within the material, resulting in a net magnetic field. Magnetization is a key concept in understanding the behavior of magnetic materials and is fundamental to the functioning of magnets and magnetic devices.
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9 Key excerpts on "Magnetization"
eBook - PDFMaterials Science and Engineering
An Introduction
- William D. Callister, Jr., David G. Rethwisch(Authors)
- 2018(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, telephones, computers, and components of sound and video repro- duction 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 20.1. Magnetic dipoles are found to exist in magnetic materials and in some respects are analogous to electric dipoles (Section 18.19).
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).
eBook - PDF- Pradeep Fulay, Jung-Kun Lee(Authors)
- 2016(Publication Date)
- CRC Press(Publisher)
With permission. 479 Magnetic Materials whereas ferroelectric behavior is seen only in insulating materials. Some of these similarities and differences will become clearer as we discuss these materials in further detail. When magnetizing field ( H ) is applied to a material, it creates Magnetization ( M ). This is equiva-lent to the application of an electric field ( E ), which creates a polarization ( P ). When we use the term magnetizing field ( H ), we are referring to an externally generated magnetic field , which is created using either a current-carrying coil or a permanent magnet. Magnetizing field ( H ) results in the creation of a magnetic flux density ( B ) or magnetic induction inside the material. When a magnetic flux ( ϕ ) is created by magnetizing field ( H ), there would be a certain number of magnetic flux lines per unit area. The number of flux lines per unit area is known as the magnetic flux density ( B ) or magnetic induction. Consider the flux density as the intensity of magnetic field at any given location in a magnetic material. The unit for flux density is Weber/square meter, written as Wb/m 2 , which is also equivalent to Tesla. The equivalent of the magnetic flux density generated due to the magnetizing field is the dielectric displacement ( D ) created by the application of an electric field. This equivalence between different elec-tric and magnetic quantities is shown in Table 11.3. Before moving forward, note that both H and B are sometimes called magnetic field. This is because both H and B play roles that electric field (E) does in Maxwell’s equations on the electric magnetic wave (Section 8.1). To prevent unnecessary confusion, we will call H and B as magnetizing field and magnetic flux density (or magnetic induction) in this book. 11.3.1 M AGNETIZING F IELD ( H ), M AGNETIZATION ( M ), AND F LUX D ENSITY ( B ) Magnetizing field is often created by passing electrical current through a wire.
eBook - PDF- Md Nazoor Khan, Simanchala Panigrahi(Authors)
- 2017(Publication Date)
- Cambridge University Press(Publisher)
5 Magnetic Properties of Materials 5.1 Introduction In contradiction to our day-to-day spoken language, without exception, scientifically, all materials are magnetic; there are no materials that can actually be called non-magnetic. The material which has the ability to respond to an externally applied magnetic field or can be magnetized is called a magnetic material. All materials can be magnetized to a varying degree of Magnetization. 5.2 Magnetic Parameters The terms which can be used to describe the concepts of magnetism are called magnetic parameters. The important magnetic parameters that are used to characterize the magnetic behaviour of materials are enumerated here. i. Magnetic dipole moment µ m : Any two equal and opposite magnetic poles separated by a small distance constitute a magnetic dipole. If pole strength of the dipole is m [Ampere × meter] and the distance from the south pole to the north pole is , the magnetic dipole moment µ m of a magnetic dipole is defined as µ = m m (5.1) The magnetic dipole moment µ m is a vector quantity, the direction being from the south pole to the north pole. The magnetic dipole moment of the current carrying loop µ m is also given as µ = m nia (5.2) 120 Principles of Engineering Physics 2 where i is the current flowing in a loop of n turns having area a . Here direction of the magnetic dipole moment µ m may be found out by applying the screw rule: (i) Place the screw at the centre of the loop perpendicular to the plane of the loop. (ii) Rotate the screw in the direction of the current flowing in the loop. (iii) The direction of linear motion of the screw is the direction of the magnetic moment of the current- carrying loop. The torque t experienced by a magnetic dipole placed in a magnetic field of induction B is given as τ µ = × m B (5.3) ii.
eBook - PDF- Patrick M. Woodward, Pavel Karen, John S. O. Evans, Thomas Vogt(Authors)
- 2021(Publication Date)
- Cambridge University Press(Publisher)
Magnetization M is conveniently described relative to the field intensity H that caused it— by volume (magnetic) susceptibility, χ v ; the susceptibility per unit volume of the material, Figure 9.4 A paramagnet is attracted into the magnetic field, diamagnet is repelled; the paramagnet will appear to weigh more in the experiment sketched. 10 Also known as the permeability of free space (or vacuum permeability), it is defined in SI units via the force of 2×10 −7 N exerted by a current of 1 A flowing in two 1-m-long and 1-m-distant parallel wires in absolute vacuum. The Laplace–Biot–Savart law then gives μ 0 . Do not confuse μ 0 with the symbol μ for the magnetic moment and μ B for Bohr magneton. The electric analogy of μ 0 is the electric constant ε 0 introduced in Section 8.1.1. 11 The electric polarization P (Section 8.1.2) is not analogous to this Magnetization M; it is analogous to the rarely used term magnetic polarization, J = μ 0 M, so that B = μ 0 H + J corresponds to Equation (8.8) for electric displacement. The use of M and not J in this book follows from the definition of the magnetic moment μ via electric current in a loop, as opposed to the alternative definition via the mechanical force moment of the magnetic pole of a magnet. The pole’s exact coordinate is not well defined for an atom, whereas electric charges are separate and can be approximated as points. 12 As do the cooperative antiferromagnetic, ferromagnetic, and ferrimagnetic materials we’ll meet later. 9.2 Physics of Magnetism 353 χ v ¼ M H (9.8) which is dimensionless in the SI system. Susceptibility is an important parameter of a magnetic material. It’s often convenient to divide χ v with the mass density (in kg/m 3 ) to obtain the mass susceptibility, χ m (in m 3 /kg). Multiplying χ m with the molar mass (in kg/ mol) 13 yields the molar susceptibility, χ mol (in m 3 /mol).
- Donald Askeland, Wendelin Wright, Donald Askeland(Authors)
- 2020(Publication Date)
- Cengage Learning EMEA(Publisher)
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 728 The first part of this equation is simply the effect of the applied magnetic field. The second part is the effect of the magnetic material that is present. This is similar to our discussion on dielectric polarization and the mechanical behavior of materials. In materials, stress causes strain, electric field (E ) induces dielectric polarization (P), and a magnetic field (H) causes Magnetization (m 0 M ) that contributes to the total flux density B. The magnetic susceptibility x m , which is the ratio between Magnetization and the applied field, gives the amplification produced by the material: m 5 M H (20-7) Both m r and x m refer to the degree to which the material enhances the magnetic field and are therefore related by r 5 1 1 m (20-8) As noted before, the m r and, therefore, the x m values for ferromagnetic and ferrimagnetic materials depend on the applied field (H). For ferromagnetic and ferrimagnetic materials, the term 0 M >> 0 H. Thus, for these materials, B > 0 M (20-9) We sometimes interchangeably refer to either inductance or Magnetization. Normally, we are interested in producing a high inductance B or Magnetization M. This is accomplished by selecting materials that have a high relative permeability or magnetic susceptibility. The following example shows how these concepts can be applied for comparing actual and theoretical Magnetizations in pure iron.
- William D. Callister, Jr., David G. Rethwisch(Authors)
- 2020(Publication Date)
- Wiley(Publisher)
C h a p t e r 20 Magnetic Properties (a) Transmission electron micrograph showing the microstructure of the perpendicular magnetic recording medium used in hard disk drives. (b) Magnetic storage hard disks used in laptop (left) and desktop (right) computers. (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. Courtesy of Seagate Recording Media Courtesy of Seagate Recording Media UmbertoPantalone/Getty Images © William D. Callister, Jr. 758 • (a) (b) (c) (d) d ) A laptop computer; one of its internal components is a hard disk drive. UmbertoPantalone/Getty Images An understanding of the mechanism that explains the permanent magnetic behavior of some materials may allow us to alter and in some cases tailor the magnetic properties. For example, in Design Example 20.1 we note how the behavior of a ceramic magnetic ma- terial may be enhanced by changing its composition. WHY STUDY the Magnetic Properties of Materials? Learning Objectives After studying this chapter, you should be able to do the following: 1. Determine the Magnetization of some material given its magnetic susceptibility and the applied magnetic field strength. 2. From an electronic perspective, note and briefly explain the two sources of magnetic moments in materials. 3. Briefly explain the nature and source of (a) diamagnetism, (b) paramagnetism, and (c) ferromagnetism. 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 materials experi- ence 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.
eBook - PDFMagnetism in Medicine
A Handbook
- Wilfried Andrä, Hannes Nowak, Wilfried Andrä, Hannes Nowak(Authors)
- 2007(Publication Date)
- Wiley-VCH(Publisher)
In contrast to the Magnetization rotation, the second type of pro- cess requires ‘‘only’’ domain wall displacements, and this can be normally be done without major effort. For this reason, the lower part of the initial Magnetization curve is usually dominated by the domain growth, whereas its behavior near satu- ration is determined by the Magnetization rotation processes. One of the most striking phenomena in ferromagnetism is the existence of the Magnetization hysteresis or the irreversibility of the Magnetization processes (Chi- kazumi, 1964; Kittel, 1986). This means that if we decrease the field magnitude starting from the saturated sample state A (Fig. 1.21), then the field dependence of the sample magnetic moment (shown by the curve AB) does not coincide with the corresponding dependence for the increasing field (curve OA). When we de- crease the field to zero, there is still some substantial net magnetic moment left – this is called the remanent magnetic moment m R . If we then reverse the field direc- tion and again increase its magnitude, a certain (often quite large) nonzero value of this field H c (called the coercive force) is needed to bring the net sample moment Fig. 1.21. Typical initial Magnetization curve O ! A and hysteresis loop. A ! B ! C ! D ! E ! F ! A for ferromagnetic materials. 54 1.2 Basic Physical Principles to zero (point C in Fig. 1.21). Further increase of the field amplitude in the nega- tive direction also leads to sample saturation in this direction (state D). Finally, by decreasing the field magnitude up to zero and then increasing it again in the positive direction, the Magnetization of our sample will follow the curve D ! E ! F ! A. So, during a complete field cycle H sat ! H sat ! H sat the sam- ple magnetic moment changes along the curve A ! B ! C ! D ! E ! F ! A, which is called the hysteresis loop.
- Anthony Wolbarst, Nathan Yanasak(Authors)
- 2019(Publication Date)
- Medical Physics Publishing(Publisher)
4.1 The Magnetization, m(x, t), of the Voxel at Location x The very weak collective magnetic field that a group of protons together produce per voxel (or per mm 3 or per gram—there has to be prior agreement on which) of material is called their voxel nuclear Magnetization, and denoted m. The Magnetization has both magnitude and direction, and is thus a vector. When we have cause to note that this is the net Magnetization in the voxel at 1D position x, we shall write it m(x). (It doesn’t matter whether we say x or x here since, in 1D, they represent the same thing.) When its magnitude or its orientation or both are varying over time, t, as well, it becomes m(x, t). The local Magnetization in each of a number of voxels will be the central player in much of the story of MRI. The data one can obtain directly from the body at any instant, however, is not the set of separate voxel Magnetizations, {m(x,t)}, one for each x-position, but rather their vector sum. The net Magnetization coming from all of them combined is The information provided by MRI comes from, and only from, monitoring the behavior of M(t) over time under different, carefully controlled circum- stances. In the remainder of this chapter, however, we shall consider what is occurring in only a single voxel over time, m(t). So for now we can do away with the x and the M altogether and focus on m(t). Later we shall explore ways to undertake the difficult and critical task of separating out each m(x,t) from M(t). (4.1) M m ( ) ( , ). t x t x 64 An Introduction to MRI for Medical Physicists and Engineers In re-introducing m(t) here, we first adopt the quasi-QM model of chapter 2. Suppose there are N pro- tons in a single voxel (Figure 4.1). At any time, the number N – (t) of them will happen to be in the lower- energy state at time t, on average, and N + (t) in the higher. And, of course, the total number of protons in the voxel is which is time-independent.
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