Neodymium magnet and NdFeB magnet
Neodymium magnets, also known as Nd-Fe-B magnets, are tetragonal crystals of Nd, Fe and B. In 1982, Sumitomo Sakawa discovered neodymium magnets with special metals. The magnetic energy product (BHmax) of this magnet was larger than that of samarium cobalt magnet, and it was the largest magnetic energy product in the world at that time. Later, Sumitomo successfully developed powder metallurgy process for special metals, and GM successfully developed melt-spinning process to prepare Nd-Fe-B magnets. This kind of magnet is the permanent magnet whose magnetism is second only to absolute zero degree holmium magnet. It is also the most commonly used rare earth magnet. NdFeB magnets are widely used in electronic products, such as hard disks, mobile phones, headphones and battery-powered tools.
In order to avoid corrosion damage, it is necessary to protect the surface of permanent magnets, such as electroplating with gold, nickel, zinc and tin, and spraying epoxy resin on the surface.