Ferrite magnet is a kind of metal oxide with ferromagnetism. In terms of electrical properties, the resistivity of ferrite is much higher than that of metal and alloy magnetic materials, and it also has higher dielectric properties. The magnetic properties of ferrite also show high permeability at high frequency. Therefore, ferrite has become a widely used non-metallic magnetic material in the field of high frequency and weak current. Due to the low magnetic energy and saturation magnetization (usually only 1 / 3 ~ 1 / 5 of pure iron) stored in unit volume of ferrite, its application in low frequency and high power fields requiring high magnetic energy density is limited.
Ferrites ferrite is a kind of non-metallic magnetic material, also known as ferrite. It is prepared by sintering ferric oxide and one or several other metal oxides (such as nickel oxide, zinc oxide, manganese oxide, magnesium oxide, barium oxide, strontium oxide, etc.). Its relative permeability can be as high as several thousand, its resistivity is 1011 times that of metal, and its eddy current loss is small, so it is suitable for making high frequency electromagnetic devices. There are five types of Ferrite: hard magnetic, soft magnetic, moment magnetic, rotational magnetic and piezomagnetic. It is also called magnetic porcelain because its production process and appearance are similar to ceramics. Ferrite is a compound oxide of iron and one or more suitable metal elements. The most important difference between ferrite magnetic materials and metal or alloy magnetic materials is conductivity. Generally, the resistivity of the former is 102-108 Ω· cm, while that of the latter is only 10-6-10-4 Ω· cm.
The earliest ferrite that China came into contact with is the natural ferrite, namely magnetite (Fe3O4), discovered in the 4th century BC. The compass invented by China is made from this kind of natural magnetite. With the development of radio technology in 1930s, ferromagnetic materials with low high frequency loss are urgently needed. However, the resistivity of Fe3O4 is too low to meet this requirement. In 1933, Japan's Tokyo Institute of technology first created a permanent magnet material containing cobalt ferrite, which was called OP magnet at that time. In the 1930s and 1940s, France, Japan, Germany, the Netherlands and other countries successively carried out the research work of ferrite. Among them, J.L. snooker, a physicist in Philips Laboratory of the Netherlands, developed various kinds of zinc containing soft ferrite with excellent spinel structure in 1935 and realized industrial production in 1946. In 1952, J.J. Venter and others developed a permanent magnetic ferrite with BaFe12O19 as the main component. The ferrite has a hexagonal structure similar to that of the four VHF magnetic ferrites studied by G.H. yongkel and others in 1956. In 1956, E.F. Berto and F. Fula reported the results of the study of the ferromagnetic y3fe5o12. The substitution ions y include PM, SM, EU, Gd, TB, Dy, Ho, er, TM, Yb and Lu. Because the crystal structure of these magnetic compounds is the same as that of natural mineral garnet, they are called garnet ferrite. Up to now, except for the amorphous ferrite materials prepared by the super quench method in 1981, the above three types of crystal structures have not been exceeded from the point of view of crystal chemistry. Most of the work is modification and in-depth research for new uses.
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