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Thermodynamics
Published in Harshad K. D. H. Bhadeshia, Theory of Transformations in Steels, 2021
Unlike diamagnetism, paramagnetism involves a magnetic moment that is proportional to the applied magnetic field. In a paramagnetic material, the spins associated with each atom are aligned at random except when the distribution is biased by an applied magnetic field. The effect is to cause the energies of those electrons more parallel to the applied field to decrease relative to those that oppose the field (Figure 2.6). To achieve a uniform Fermi potential, some of the electrons transfer from states with spins anti-parallel to the applied field, to those where the spin is parallel. This leaves a net imbalance in the spins. The resultant magnetisation depends on the excess number of spins. The effect is much smaller than if all electrons were able to change their spins to lie parallel with the field, but this is not permitted by the Pauli exclusion principle. Paramagnetism is therefore a weak effect which reinforces the applied field. Because diamagnetism is associated with negative susceptibility, it reduces the contribution of paramagnetism by about a third according to the Landau theory.
Permanent Magnet Motors and Halbach Arrays
Published in Ranjan Vepa, Electric Aircraft Dynamics, 2020
Paramagnetic materials are generally attracted to magnetic fields. They have a relative magnetic permeability greater than one (or, equivalently, a positive magnetic susceptibility). For low levels of magnetization, Curie’s law is a good approximation for the magnetization of paramagnets is given by M=χH=(C/T)H where M is the resulting magnetization or magnetic moment, χ is the magnetic susceptibility, H is the auxiliary magnetic field, measured in amperes/meter, T is absolute temperature, measured in K and C is a material-specific Curie temperature.
fMRI and Nanotechnology
Published in Sarhan M. Musa, Nanoscale Spectroscopy with Applications, 2018
Aditi Deshpande, George C. Giakos
We know that based on their magnetic properties, materials can be classified as diamagnetic, paramagnetic, or ferromagnetic. Nearly 99% of the tissues in the body are diamagnetic, which is why there is little or no interest in developing contrast agents using diamagnetic materials [19]. Paramagnetic materials possess unpaired electrons and can be used to enhance magnetic relaxation in MRI. These paramagnetic ions bind to the water molecules and tumble (thermally vibrate) in solution, creating a random oscillating magnetic field. This generated field affects the precessing nuclei. When an interaction takes place between the paramagnetic ions and the magnetized protons increase, the rate of relaxation of the neighboring protons and the presence of an additional magnetic field created by these materials increase the dephasing between the protons. In this way, the relaxation time (both Tl and T2) is reduced and therefore enhanced by the use of an external paramagnetic contrast agent. To decrease the toxicity of paramagnetic materials, they are typically chelated with organic ligands before being administered for imaging.
Elimination of Diethylenetriaminepentaacetic Acid from Effluents from Pharmaceutical Production by Ozonation
Published in Ozone: Science & Engineering, 2022
Fares Daoud, Sebastian Zühlke, Michael Spiteller, Oliver Kayser
However, there are also expedient applications for earth alkali and heavy metals in medical systems. One example is the field of diagnostic imaging. The paramagnetic properties of some elements can be used in magnetic resonance imaging (MRI) to resolve certain areas of the human body in more detail. One of these elements is the lanthanide gadolinium (Gd). The outer electron shell of gadolinium has seven unpaired electrons, which leads to its extreme paramagnetism. However, it is highly toxic in the ionic form, with the LD50 of 0.1 mmol/kg of body weight (Vogl 2013), and therefore harmful when employed for MRI applications. Instead, gadolinium is used in a ligated form that is very stable and unable to permeate the blood–brain barrier. However, some Gd-based contrast agents were reported to cause nephrogenic systemic fibrosis, likely related to dechelation, in several patients. Further, considerably higher resistance to chelate disruption was observed in the so-called macrocyclic forms of gadolinium-based contrast media, as compared to their linear counterparts (Montagne, Toga, and Zlokovic 2016). The complexing agent, DPTA forms such stable ligands with gadolinium, resulting in a nontoxic structure, without compromising its effectiveness in MRI applications.
Magnetic characterizations of nickel hyperaccumulating plants (Planchonella oxyhedra and Rinorea bengalensis) from Halmahera, Indonesia
Published in International Journal of Phytoremediation, 2019
Abd Mujahid Hamdan, Satria Bijaksana, Aiyen Tjoa, Darharta Dahrin, Kartika Hajar Kirana
As can be seen in Figure 3, the magnetic properties of hyperaccumulators and non-hyperaccumulators are considerably different. The magnetic susceptibility values of hyperaccumulators are positive, but those of non-hyperaccumulators are negative. The difference in χ values can be attributed to the abundance of Ni in the hyperaccumulators. These results are significant and warrant further study, as they could serve as a basis for using magnetic measurements for the identification of new species of hyperaccumulator. Prospective hyperaccumulators could be identified by their positive magnetic susceptibility and non-hyperaccumulators by their negative magnetic susceptibility. Most organic materials are diamagnetic (Estrada et al. 2000), but they can also be paramagnetic if they contain transition metals, such as Ni, as a central atom of organometallic complexes (Jensen et al. 2007; Schlueter 2009). Organometallic compounds in plants can be paramagnetic, e.g., plastocyanins (Urlich 1978) and ferredoxin (Bertini et al. 1993).
Designing of a magnetically separable Fe3O4@dopa@ML nano-catalyst for multiple organic transformations (epoxidation, reduction, and coupling) in aqueous medium
Published in Journal of Coordination Chemistry, 2019
Sanchari Dasgupta, Sourav Chatterjee, Tanmay Chattopadhyay
Paramagnetic materials are useful for ease of their separation from reaction mixture with the help of external magnetic field. The magnetization behavior of Fe3O4, Fe3O4@dopa and Fe3O4@dopa@ML were studied under applied magnetic field and are shown in Figure 6. A decrease in the values of saturation magnetization (Ms) value from Fe3O4 (54.03 emu g−1) to Fe3O4@dopa (43.02 emu g−1) to Fe3O4@dopa@ML (27.68 emu g−1) occurs due to gradual increment of organic moiety, i.e. diamagnetic part from Fe3O4 to Fe3O4@dopa@ML. However, the net magnetism exhibited by the newly synthesized nano-catalyst is sufficient for effective separation from the reaction mixture by an application of external magnetic field (Figure 7).