Neodymium sintered magnets (Nd-Fe-B), NdFeB Magnet
From among the group of modern magnets of rare earth-metal (Re-M) type, neodymium sintered magnets (Nd-Fe-B) achieved the biggest market success. They owe their excellent magnetic properties to Nd2Fe14B compound, discovered in 1984. The very magnets are manufactured using methods of powder metallurgy, and thanks to pressing in a magnetic field, or plastic working in elevated temperature, they get anisotropic structure. Maximum energy density (BH)max (ca. 400 kJ/m3) of the magnets is very high. They also have high values of remanence induction Br, similar to those of alnico magnets; fields of their coercive force jHc are repeated dozens of times higher, which make possible to install them under strong demagnetizing fields. Compared with samarium-cobalt magnets they show a smaller range of working temperatures, and their magnetic properties depend, in a considerably greater measure, on temperature. Due to the contents of neodymium that shows big susceptibility to oxidation, the magnets are coated with thin anticorrosive layers. Ni, Zn, Ni-Zn lub Ni-Cu-Ni are the most often applied layers. It is also possible to coat the magnets with plate, gold, gold-nickel layers, apply phosphate coating or epoxidation.