Ferromagnetic Materials
Ferromagnetic materials are substances that exhibit strong magnetic properties, such as iron, nickel, and cobalt. They can be magnetized and retain their magnetization, making them useful in a wide range of technological applications, including electric motors, transformers, and magnetic storage devices. These materials are characterized by their ability to form permanent magnets and to attract other ferromagnetic materials.
7 Key excerpts on "Ferromagnetic Materials"
eBook - ePub- Bill Mantovani(Author)
- 2019(Publication Date)
- In Easy Steps Limited(Publisher)
...Sometimes the magnetic field is quite large and easily detected, but similarly, sometimes it is so small that it is very difficult to detect its existence. Many metals have a magnetic field. The effect is strongest in metals where the atoms are grouped together in a way that produces tiny individual magnets. When these miniature magnets are all correctly aligned, either naturally or through the influence of another magnet or electric current, the material itself becomes a magnet. Iron has excellent magnetic properties. Materials that behave in this way are called Ferromagnetic Materials. Magnetism and electricity are very strongly linked. Whenever a current flows, a magnetic field is created. This effect can be put to good use – for example, in creating what is called an electromagnet. A coil is wound around a piece of metal that has virtually no magnetic field of its own. When a current is passed through the coil then a magnetic field is created. When the current is switched off, the magnetic field disappears. Very large electromagnets are often seen in use in scrap metal yards, such as for picking up a car body and dropping it into a crusher. Early records show that magnetism was being used as a navigation aid in ancient China. Ferromagnetic material is the term given to a metal whose molecules move freely and so can be easily made to line up and so turn it into a magnet. Magnetic Field All magnets have a magnetic field that surround them and that is strong enough to have an influence on other materials. As the name suggests, a permanent magnet is surrounded by a permanent magnetic field and, as you learned here, is typically a piece of ferromagnetic material. However, not all Ferromagnetic Materials are permanent magnets. In some, the molecules only temporarily line up when the material is placed in the presence of a strong magnetic field to form a temporary magnet...
eBook - ePubRad Tech's Guide to MRI
Basic Physics, Instrumentation, and Quality Control
- William H. Faulkner, Euclid Seeram(Authors)
- 2020(Publication Date)
- Wiley-Blackwell(Publisher)
...In this event, since the paramagnetic effects are stronger, the substance exhibits paramagnetic characteristics. Ferromagnetic substances are similar to paramagnetic substances in that they become magnetized when placed in an externally applied magnetic field. Ferromagnetic substances, however, will remain magnetized when the externally applied field is removed. Iron is an example of a ferromagnetic substance. A dipole is a magnet with two poles: north and south. By convention, the magnetic field of a dipole runs from the north pole around to the south pole. When two identical poles are brought together, the resultant fields oppose each other and thus they repel. When two opposite poles are brought together, the resultant fields combine and the two magnets are pulled toward each other. The strength of a magnetic field is expressed in terms of Gauss or Tesla. Gauss is the CGS (Centimeter‐Gram‐Second) unit of magnetic flux density. Tesla is the International Standard (SI) unit of magnetic flux density. The earth's magnetic field strength is approximately 0.5 G. One Tesla equals 10 000 G. Nuclear Magnetism In the early days of MRI, the term nuclear magnetic resonance (NMR) was used. The word nuclear, however, elicited visions of radioactivity, thus the name was changed to MRI. In reality, the term nuclear as it is used in NMR refers to the nucleus of atoms. Atoms which have an odd number of protons in their nucleus are “magnetically active.” This means that certain nuclei have properties that cause them to display magnetic characteristics...
eBook - ePubMaterials
Engineering, Science, Processing and Design
- Michael F. Ashby, Hugh Shercliff, David Cebon(Authors)
- 2009(Publication Date)
- Butterworth-Heinemann(Publisher)
...Most materials achieve near-perfect cancelation either within the atomic orbits or—if not—by stacking the atomic moments head to tail or randomising them so that, when added, they cancel. A very few, most based on just three elements—Fe, Ni and Co—have atoms with residual moments and an inter-atomic interaction that causes them to line up to give a net magnetic moment or magnetisation. Even these materials can find a way to screen their magnetisation by segmenting themselves into domains: a ghetto-like arrangement in which atomic moments segregate into colonies or domains, each with a magnetisation that is oriented such that it tends to cancel that of its neighbors. A strong magnetic field can override the segregation, creating a single unified domain in which all the atomic moments are parallel, and if the coercive field is large enough, they remain parallel even when the driving field is removed, giving a ‘permanent’ magnetisation. There are two sorts of characters in the world of magnetic materials. There are those that magnetise readily, requiring only slight urging from an applied field to do so. They transmit magnetic flux and require only a small reversal of the applied field to realign themselves with it. And there are those that, once magnetised, resist realignment; they give us permanent magnets. The charts of this chapter introduced the two, displaying the properties that most directly determine their choice for a given application. 15.7 Further reading Braithwaite N., Weaver G. Electronic Materials 1990 The Open University and Butterworth-Heinemann Oxford, UK ISBN 0-408-02840-8. (One of the excellent Open University texts that form part of their materials program.) Campbell P.. Permanent Magnetic Materials and Their Applications. Cambridge, UK: Cambridge University Press; 1994. Douglas W.D. Magnetically soft materials, in ASM Metals Handbook Properties and Selection of Non-ferrous Alloys and Special Purpose Materials 9th ed...
eBook - ePubNanoparticles - Nanocomposites – Nanomaterials
An Introduction for Beginners
- Dieter Vollath(Author)
- 2013(Publication Date)
- Wiley-VCH(Publisher)
...8 Magnetic Nanomaterials, Superparamagnetism 8.1 Magnetic Materials On putting any material into a magnetic field, one observes two, more or less distinct, reactions: the material is pulled into the magnetic field – paramagnetic behavior – or it is repelled from the magnetic field – diamagnetic behavior. Both reactions are connected to the electronic structure of the atoms, molecules, or solids. Any material is diamagnetic; however, in many cases, this diamagnetism is superimposed by paramagnetism, which is stronger; therefore, these materials belong to the group of the paramagnetic materials. Diamagnetism is caused by the movement of the electrons around the atomic nucleus. According to Faraday 's law of magnetism (more specifically known as Lenz 's rule) the magnetic field caused by the circular motion of the electrons is oriented opposite to the external field. The electrons move not only around the nucleus, they also rotate around their axis. This spin of the electrons also causes a magnetic moment. In cases, where the electrons are paired, the spins are directed opposite. Therefore, in an atom with an even number of electrons, the magnetic moments of the spins compensate each other; these atoms are diamagnetic. All the other atoms are paramagnetic. The same rules are valid in the case of compounds. For the further discussion in connection to nanoparticles and nanomaterials, only paramagnetic materials in their different varieties are of importance. Figure 8.1 displays the situation for a crystallized solid without an external magnetic field. This figure shows the cases where the orientation of the elementary dipoles are disordered, paramagnetism, and the one, with ordered magnetic dipoles, ferromagnetism. In Ferromagnetic Materials, the dipoles interact; a process leading to a long-range ordering, lining up the dipoles parallel, or in the case of antiFerromagnetic Materials, antiparallel...
eBook - ePubAdvances in Paleoimaging
Applications for Paleoanthropology, Bioarchaeology, Forensics, and Cultural Artefacts
- Gerald J. Conlogue, Ronald G. Beckett(Authors)
- 2020(Publication Date)
- CRC Press(Publisher)
...Ferromagnetic material, such as iron, is strongly attracted to magnets. Diamagnetic materials, such as gold, aluminum, and most body tissues save for dense cortical bone, are weakly repelled. Paramagnetic material, such as gadolinium, is weakly attracted. Nonmagnetic materials, such as glass, ceramic, and wood, are not affected at all by magnets. In the clinical world, these distinctions are important for a variety of reasons such as image quality, safety, and understanding pathological processes. When discussing paleoforensic imaging, a strong understanding of how materials affect the magnetic fields is essential for proper image planning as the specimens to be imaged are frequently treated or exposed to substances that can alter their imaging properties. The magnetic field that we experience when walking about on the Earth is relatively low and equivalent to about 0.5 gauss (G). A “gauss” is a unit of measure frequently used for weak magnetic-field measurement in medical imaging. It is strong enough that a ferromagnetic compass needle can indicate the direction of the magnetic north pole; however, it is not of sufficient strength for imaging purposes. The unit of magnetism employed for the stronger fields used for imaging purposes is the tesla (T), named after Nikola Tesla, who did extensive research with electricity and magnetic fields. One tesla equals 10,000 G. For high-field MRI, the magnetic field strength is 1.5 to 3 T, or roughly 30,000 to 60,000 times stronger than the Earth’s geomagnetic field. Now back to the H 1 protons. Normally, these protons are randomly aligned throughout the body (Figure 8.1). When a strong external magnetic field is applied (B O), the protons are forced into alignment with the overwhelmingly more powerful external field. They tend to align either parallel (low energy) or antiparallel (high energy) to the field (Figure 8.2). Since nature favors a lower energy state, there will be a greater number of parallel protons...
eBook - ePubMagnetic Resonance Imaging
Physical Principles and Sequence Design
- Robert W. Brown, Y.-C. Norman Cheng, E. Mark Haacke, Michael R. Thompson, Ramesh Venkatesan(Authors)
- 2014(Publication Date)
- Wiley-Blackwell(Publisher)
...These differences will manifest themselves as signal changes in both magnitude and phase images, and can be used to diagnose or extract important information about body function. We begin by laying out brief descriptions of different magnetic behavior of various material, the ‘isms’ of para-, dia-, ferro-, antiferro-, ferri-, and superparamagnetism. The magnetic susceptibility and permeability parameters in the field equations are considered next. These parameters can be strong functions of positions, especially at tissue interfaces and in the vicinity of contrast agent particles; thus, objects embedded in the background material are studied in the third section. The full expressions for the local field for both a sphere and an arbitrarily oriented cylinder are presented. The remainder of the chapter is devoted to the blood oxygenation dependent susceptibility in functional MRI. 25.1 Paramagnetism, Diamagnetism, and Ferromagnetism Inside of a body, a spin is subject to an internal field due to its neighbors, in addition to any external field. The internal field is dominated by the nearby atomic electrons, and individually their contributions can be well approximated by magnetic dipole fields corresponding to the magnetic dipole moments associated with their orbital and spin degrees of freedom. Neighboring nuclear magnetic moments are reduced in importance owing to the inverse-mass dependence first noted in Ch. 2, but the existence and size of the atomic moment is also based on the question of whether there are unpaired constituents, in this case the atomic electrons. The electron magnetic moments are intrinsic or can be induced and, in this section, the classification of materials according to the different kinds of magnetic dipole moments is laid out. 25.1.1 Paramagnetism The quantum stacking of electrons in an atom or molecule involves a systematic cancelation of spin moments for each pair...
eBook - ePubApplied Welding Engineering
Processes, Codes, and Standards
- Ramesh Singh(Author)
- 2011(Publication Date)
- Butterworth-Heinemann(Publisher)
...These poles attract the magnetic particles more strongly than the surrounding surface of the material, thus making it clearly visible against the contrasting background or under fluorescence of black light. The most apparent characteristic of a magnet is its ability to attract any magnetic material placed within its field. This property is attributed to a line of force that passes through the magnetic materials, since they offer a path of lower reluctance than a path through the surrounding atmosphere, and these lines of force tend to converge in to the magnetic material. The object for inspection is magnetized, either by an electromagnet or by a permanent magnet. In a permanent magnet system, the North and South Poles are at opposite ends; this is a longitudinal magnetization. These poles produce imaginary lines of force between them to create a magnetic field in the surrounding material. This is explained by the following experiment with a bar magnet. If a bar magnet is notched as shown in Figure 3-4-1 below, the flux distribution or flow of the lines of force will be markedly changed in the area surrounding the notch. The distortion in the line diminishes as the distance from the breach in the magnetic field increases. In this condition each face of the notch assumes an opposite polarity, producing a flow of leakage flux across the air gap. It is this leakage flux that permits the detection of defects by the magnetic particle method. Irrespective of what method is used to magnetize the test object, its magnetic field remains the principle of the method. Figure 3-4-1 Magnetic field and flux leakage. The electromagnetic method is used more often. In this method the test object is magnetized by introducing a high current, or by putting the test object in a current-carrying coil. The magnetic field in the test piece is interrupted by any discontinuities, producing a magnetic field leakage on the surface...
