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Ferromagnetism
Published in Daniel D. Pollock, PHYSICAL PROPERTIES of MATERIALS for ENGINEERS 2ND EDITION, 2020
The energy product is a more specific criterion for the selection of magnetic materials. This is found for any given point on a B-H curve by the product of B and H. The energy product curve for a given material is obtained when this is done for a sufficient number of points taken from a B-H curve. The maximum energy product, (BdHd)max, is considered by many engineers to be the best individual basis for the comparison and selection of permanent magnet materials. However, it is most prudent to consider both the demagnetization curve, giving Br and Hc, and the maximum energy product. Both curves are shown in Figure 9-27
Finite-Element Magnetostatic Solutions
Published in Stanley Humphries, Field Solutions on Computers, 2020
Equation 9.70 shows that Ug is proportional to the magnet volume — we can achieve higher fields by buying larger magnets. We can also maximize the field energy by seeking an operating point that gives the highest value of B||Bo||, thereby using the material most effectively. The bracketed quantity in Equation 9.70 is called the energy product and has units of J/m3. The energy product is a measure of material quality. The maximum energy product for a ceramic magnet is about 10 kJ/m3 compared with values exceeding 100 kJ/m3 for neodymium-iron.
Permanent Magnet Motors and Halbach Arrays
Published in Ranjan Vepa, Electric Aircraft Dynamics, 2020
Ferromagnetic material magnets offer high levels of performance owing to their very high maximum energy product (MEP) compared to other magnetic materials. The maximum energy product is the measure of the magnetic energy which can be stored, per unit volume, by a magnetic material.
High performance hot-deformed Nd-Fe-B magnets (Review)
Published in Science and Technology of Advanced Materials, 2021
Nd-Fe-B magnets with the highest maximum energy product (BH)max of all permanent magnet materials were independently invented by Sagawa et al. [1] and Croat et al. [2] in 1982. Sintered Nd-Fe-B magnets by Sagawa [1] were the mainstream high-performance magnets because of their high magnetic properties and productivity. The rapid-quenched Nd-Fe-B powder by Croat et al. [2] was used as a raw material for bonded Nd-Fe-B magnets and hot-deformed Nd-Fe-B magnets [3]. Although sintered and hot-deformed Nd-Fe-B magnets have very similar magnetic properties, they differ in terms of their microstructures; hot-deformed Nd-Fe-B magnets have a fine microstructure (diameter of 200–500 nm), this is one order of magnitude finer than the sintered magnets.
Production of M-type strontium hexaferrite magnetic powder with the high-pure magnetite concentrate via the ceramic process
Published in Journal of Asian Ceramic Societies, 2022
Yujuan Zhou, Tao Jiang, Bin Xu, Yuming Lin, Min Zhang, Lanming Liu, Shouguo Zhong, Chengzhi Wei, Yufeng Chen, Yongbin Yang, Qian Li
It is widely accepted that magnetic properties of magnetic powder are evaluated by testing its sintered ferrite magnet in industry. As depicted in Figure 2, the production of ferrite magnet from magnetic powder includes procedures of grinding, draining, wet-compacting in a magnetic field, sintering, and polishing. The values of remanence (Br), magnetic coercive force (Hcb), Hcj, and the maximum energy product (BHmax) of ferrite magnet were calculated from the demagnetization curves obtained by the permanent magnetic measuring system. To deeply understand the difference between HPMC and iron scrap in producing magnetic powder as iron-containing raw materials, comparative experiments were carried out.
Most frequently asked questions about the coercivity of Nd-Fe-B permanent magnets
Published in Science and Technology of Advanced Materials, 2021
Jiangnan Li, Hossein Sepehri-Amin, Taisuke Sasaki, Tadakatsu Ohkubo, Kazuhiro Hono
Nd-Fe-B-based permanent magnets, independently invented by Sagawa [1] and Croat [2] in 1982, are one of the most important industrial materials that are used as magnetic field sources for motor, generator and actuators. It is foreseen that the needs for the high-performance Nd-Fe-B-based permanent magnets will increase further due to the rapid expansion of applications in green energy sectors such as motors and generators for electric vehicles, drones, robots, and wind turbines [3]. Although the maximum energy product of Nd-Fe-B is approaching its theoretical limit, the coercivity that is the most important extrinsic properties for permanent magnet application is still far below their theoretical limits. Physically, the coercivity of permanent magnets should scale with the anisotropy field of ferromagnetic compounds, HA; however, the typical coercivity values of commercial polycrystalline sintered magnets are only around 0.2 HA, which is known as Brown’s paradox. For example, the typical value of coercivity, µ0Hc, for N50 type magnet with (BH)max~4 00 kJ/m3 is ~1.2 T, which is only ~15% of the anisotropy field of the Nd2Fe14B compound (µ0HA ~ 7.5 T) [4,5]. Due to the thermal demagnetization effect, coercivity decreases to ~0.2 T at ~160°C, which is the operating temperature of the magnet in the traction motor of (hybrid) electric vehicles. The industrial solution for this was to substitute part of Nd in the Nd2Fe14B lattice with Dy to increase the anisotropy filed [4]. The resultant coercivity of (Nd0.7Dy0.3)-Fe-B magnets reaches 3.0 T. However, limited natural resources for Dy and its supply risks have raised research interest to develop high coercivity Dy-free Nd-Fe-B magnets with a better thermal stability of coercivity [6,7].