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Magnetic Circuits
Published in Zeki Uğurata Kocabiyikoğlu, Electromechanical Energy Conversion, 2020
The coercivity can be thought of as the magnitude of the mmf required to demagnetise the material. From the hysteresis loop of Figure 2.26, it is clear that there is an element of uncertainty in the results of the analysis of the magnetic circuits. There are two values of B against a specific value of H, and which value is applicable depends on the previous magnetic history of the circuit. To determine the true value of B, we must look whether H is ascending or descending. The line Oa3a2a1 joining the tips of successive hysteresis loops is usually taken to be the average (normal) magnetisation curve of that particular material. This is known as a DC or normal magnetisation curve.
Magnetic and Electrical Properties
Published in Elaine A. Moore, Lesley E. Smart, Solid State Chemistry, 2020
Elaine A. Moore, Lesley E. Smart
Magnetic strips are the brown or black strips found on many plastic cards, such as debit and credit cards. They were first used on the London Underground in the 1960s and were introduced into credit cards in the 1970s. They consist of small crystals of a magnetic material in a resin. A material commonly used for this is barium ferrite (BaFe2O4). Data such as your name and account number are encoded in the strip by altering the direction of the magnetisation of some crystals. Each character is represented by a set of crystals, some magnetised in one direction to represent 1 and others magnetised in the opposite direction to represent 0. When the card is swiped, the direction of the magnetisation is detected. High-coercivity materials, such as barium ferrite, are used as they retain their magnetisation so that the data are not accidentally erased.
Permanent Magnet Motors and Halbach Arrays
Published in Ranjan Vepa, Electric Aircraft Dynamics, 2020
MEP is calculated as the maximum product of a material’s residual magnetic flux density (degree of magnetization) and its coercivity is the ability to resist demagnetization once magnetized. In NdFeB, the remnant flux density and coercivity are both significantly higher than for other magnetic materials. Coercivity and remanence are both related to the tendency of some ferromagnetic materials to retain a magnetic field after an externally applied field is removed. Remanence is the flux density which remains, and coercivity is a measure of the field strength which must be applied to reduce the remnant flux to zero.
Recent progress in the development of high-performance bonded magnets using rare earth–Fe compounds
Published in Science and Technology of Advanced Materials, 2021
Takashi Horikawa, Masao Yamazaki, Masashi Matsuura, Satoshi Sugimoto
The disproportionated structure is related to the grain size of the recombined Nd2Fe14B in d-HDDR [44]. As shown in Ref [44], the tHD dependence of the area fraction of coarse Nd2Fe14B grains (600–1200 nm) was similar to that of Sf and DOA in Figure 4. Furthermore, the misorientation angle of the [001] of Nd2Fe14B was found to be small (<20°) in the coarse Nd2Fe14B grain region, but was larger (<36°) in the fine Nd2Fe14B grain region. In addition, the fine lamellar colonies (740–920 nm) and coarse grains (600–1200 nm) were similar in size. This finding suggests that fine lamellar structures form coarse Nd2Fe14B grains after recombination, and thus fine recombined Nd2Fe14B grains (200–600 nm) were thought to originate from the coarse lamellar and/or spherical structures. It is well known that coercivity strongly depends on grain size and increases with decreasing grain size. This relationship is consistent with the tHD dependence of coercivity shown in Figure 4, where high coercivity is obtained when the disproportionated structure is composed of coarse lamellar or spherical structures and forms fine recombined Nd2Fe14B grains.
Oil spill cleanup using industrial and agricultural waste-based magnetic silica sorbent material: a green approach
Published in Green Chemistry Letters and Reviews, 2021
Narendra Kumar, Sudhir S. Amritphale, John C. Matthews, Joan G. Lynam
The chemical composition of red dust is shown in Table S1 (Online Resource 1). The red dust was found to be magnetic in nature. It contained iron in the form of hematite, magnetite, and wüstite. The magnetite is a ferromagnetic phase with high magnetization (∼92 Am2 kg−1) and low coercivity (10–40 mT) whereas hematite is anti-ferromagnetic with low magnetization [∼0.4 Am2 kg−1] and high coercivity (100–400 mT). Coercivity is the resistance of a ferromagnetic material to becoming demagnetized. The magnetization of different phases are linearly additive in non-interacting mixtures (29). Sodium oleate has a high affinity for the surface of iron oxide particles (30) in red dust. Mixing of functionalized RHA/SCBA with red dust resulting in the MSS becoming responsive towards the external magnetic field and selectively adsorbing the oil on the water surface.
Microstructure and properties of Cu-Fe alloys fabricated via powder metallurgy and rolling
Published in Powder Metallurgy, 2021
Chenzeng Zhang, Cunguang Chen, Lina Huang, Tianxing Lu, Pei Li, Wenwen Wang, Fang Yang, Alex A. Volinsky, Zhimeng Guo
Coercivity (Hc) is also one of the important parameters of magnetic materials. From the results of the magnetic hysteresis loop, the coercivity increased with the increase of Fe content and after annealing. Before heat treatment, the coercivity of CFA 5, CFA 10 and CFA 30 was 56.3, 65.6 and 85.1 Oe, respectively. After annealing at 400°C, the coercivity correspondingly increased to 66.4, 73.5 and 98.2 Oe. The coercivity came from the irreversible magnetisation process, so the factors that affected the irreversible magnetisation process, such as magnetic anisotropy, impurities, pores, dislocations and other defects will affect the coercivity, which is a structure-sensitive parameter [37,38]. In this experiment, Fe particles were ferromagnetic, and each particle was the single domain. The magnetic moment increased with the number of Fe particles, which led to the increased magnetic anisotropy energy, and the greater the block to the reverse magnetisation process, the stronger magnetic field was needed for magnetisation reversal. Additionally, the phase interface increased with the Fe content, resulting in greater structural distortion. In the process of the domain wall displacement or rotational magnetisation, these phase interfaces and distortions hindered the domain wall displacement, and dislocations would also bring about the increase of spin pinning position, which were the reasons for the increased coercivity [10].