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.
5 Key excerpts on "Diamagnetism"
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 - ePubFundamentals of Electric Machines: A Primer with MATLAB
A Primer with MATLAB
- Warsame Hassan Ali, Matthew N. O. Sadiku, Samir Abood(Authors)
- 2019(Publication Date)
- CRC Press(Publisher)
...Thus, the piece of the electromagnetic material may not have a total magnetic torque, but when placed within an external magnetic field, the inhibition of the individual fields will go together in the same direction forming a total determination. So, the notable magnetic property of the ferromagnetic material is to turn into another kind of magnetic material at Curie temperature. The elements Fe, Ni, and Co are typical ferromagnetic materials which are characterized by the ability to attract and repulse with other magnetic objects. FIGURE 1.2 Magnet applications in the loudspeakers. Paramagnets : This substance that shows a positive response to the magnetic field, but it’s a weak response. The amount of response is determined by a standard called magnetic susceptibility, which represents the ratio of the magnetic force of the material to the magnetic field strength, which is a quantity without units. The paramagnetic phenomenon is observed in substances whose atoms contain single electrons (while these electrons are usually conjugal and opposite), so its magnetic torque can’t be zero. Paramagnetic materials include transient and rare substances in nature or generally substances whose atoms contain non-conjugate electrons. The magnetic properties of these substances depend on the temperature. Examples of these substances are sodium, potassium, and liquefied oxygen. Diamagnetism : Is the material that is generated when placed within an external magnetic field, an opposition torque that contradicts the direction of the outer field and explains that as a result of the currents that are excited in atoms of the material with non-bilateral electrons are generated according to the law of Ampere of an opposite that contrasts with the field caused by this note that these materials contradict with magnets close to them. The relative permeability of these materials is slightly less than one, i.e., their magnetic intensity is negative...
eBook - ePubGateway to Condensed Matter Physics and Molecular Biophysics
Concepts and Theoretical Perspectives
- Ranjan Chaudhury(Author)
- 2021(Publication Date)
- Apple Academic Press(Publisher)
...Thus, our simple calculation presented above shows that no magnetization is induced in a classical system even in the presence of an external magnetic field, in thermodynamic equilibrium. The above analysis clearly implies that magnetism of materials, as observed, will have to be essentially a quantum phenomenon. Therefore, we will have to deal explicitly with the quantum mechanical Hamiltonians for describing all types of magnetism. To clarify this point, for example, even though the phenomenon of Diamagnetism is a universal one and is based on the property of classical electromagnetic induction, the finite diamagnetic response is only obtainable in a fully quantum mechanical treatment of the material system which is coupled to the electromagnetic field. For the other forms of magnetism, however, the microscopic origin itself is quantum mechanical besides the necessity of using quantum variables in the Hamiltonian. The phenomenon of Diamagnetism or more precisely, orbital Diamagnetism is a universal one, as stated before. Every system in this universe exhibits diamagnetic response, i.e., negative magnetic susceptibility. Its magnitude, i.e., the absolute magnitude of the diamagnetic susceptibility, however, is generally quite small and is very often masked by the higher magnitude of the spin response (positive magnetic susceptibility) from the other forms of magnetism like paramagnetism. The only exceptions are superconductors and some of the band insulators. These above-mentioned systems behave as “super-diamagnets,” where the diamagnetic susceptibility attains the highest value possible v i z. − 1 4 π.. Moreover, these systems have vanishingly small spin susceptibilities. As a result, the overall magnetic response of these systems is very prominently diamagnetic. The origin of orbital Diamagnetism is electromagnetic induction, as has been pointed out before...
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 - 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...
