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Magnetic materials are mainly divided into two categories: soft magnets and permanent magnets
Magnetic materials are mainly divided into two categories: soft magnets (also known as electromagnets) and permanent magnets (also known as hard magnets). Ferrite manufacturers need external power to produce magnetic force, and the latter itself has the characteristic of maintaining magnetic force. The development of permanent magnetic materials has gone through many historical stages (Figure 1). Starting from magnets at the end of the 19th century, the main indicator of magnetic energy product has increased by 200 times in 100 years.
The discovery of AlNiCo permanent magnets in the 1930s was a milestone in the history of the development of permanent magnetic materials. Alnico permanent magnet working temperature can be as high as 600 degrees or more, mainly used in areas with high temperature stability requirements, such as instrumentation, electrical appliances, electro-acoustic telecommunications, magnetic transmission devices and aerospace devices. AlNiCo permanent magnets once occupied the leading position in the permanent magnet market in the 30th and 60th centuries of the 20th century. By 1972, its output had occupied 40% of the total permanent magnet production of all magnet manufacturers. However, due to the fact that this alloy contains expensive strategic material cobalt, especially due to the cobalt crisis in the 1970s, its application was gradually replaced by ferrite permanent magnets discovered in the 50s and rare earth permanent magnets discovered in the late 1960s. In 1982, AlNiCo permanent magnet production only accounted for 8% of the world's permanent magnetic material production.
Ferrite permanent magnet is the second most permanent magnetic material after AlNiCo permanent magnets. It is mainly composed of barium ferrite and barium ferrite. It has high resistivity and large coercive force and can be effectively used. In an air-gap magnetic circuit, it is particularly suitable as a permanent magnet for small-sized generators and motors. The permanent magnet ferrite does not contain precious metals such as nickel and cobalt, and has a rich source of raw materials, a simple process, and a low cost, and can be used instead of AlNiCo permanent magnets to manufacture magnetic separators, magnetic thrust bearings, loudspeakers, and microwave devices. However, its maximum energy product is low, its temperature stability is poor, its texture is brittle, it is fragile, it is not resistant to shock and vibration, and it is not suitable for measuring instruments and magnetic devices with precise requirements.
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