Permanent magnets can be natural products, known as natural magnets, or can be artificial products (the strongest permanent magnet is neodymium magnet). Non-permanent magnets are magnetic only under certain conditions, and are usually produced in the form of electromagnets, which use electric current to strengthen their magnetic field.
The first category is metal alloy magnets, including neodymium iron boron magnets (NdFeB), samarium cobalt magnets (SmCo), aluminum nickel cobalt magnets (ALNiCo). The second category is ferrite permanent magnet materials (Ferrite).
1. Neodymium iron boron magnet: It is the magnet with the highest commercial performance currently found. It is called the king of magnetic which has extremely high magnetic performance. And its maximum magnetic energy product (BHmax) is more than 10 times higher than that of ferrite. Its own machining performance is also quite good. The maximum working temperature can reach 200℃. Moreover, its hard texture, stable performance, and good cost performance make its application extremely wide. However, because of its strong chemical activity, it must be coated by Zn, Ni, electrophoresis, passivation, etc. on the surface.
2. AlNiCo magnet: It is an alloy composed of aluminum, nickel, cobalt, iron and other trace metal elements. The casting process can be processed into different sizes and shapes, and the workability is very good. Cast AlNiCo permanent magnets have the lowest reversible temperature coefficient, and the working temperature can be as high as 600℃. AlNiCo permanent magnetic products are widely used in various instruments and other applications.
3. Samarium cobalt (SmCo) is divided into SmCo5 and Sm2Co17 according to different compositions. Due to the high price of its materials, its development is restricted. SmCo, as a rare earth permanent magnet, not only has a high magnetic energy product (14-28MGOe), reliable coercivity and good temperature characteristics, but is more suitable for working in high temperature environments compared with neodymium iron boron magnets.
4. Ferrite magnet: Its main raw materials include BaFe12O19 and SrFe12O19. Manufactured by ceramic technology, the texture is relatively hard, while it is a brittle material. Because of good temperature resistance, low price and moderate performance, ferrite magnet has become the most widely used permanent magnet.