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The main components of ferrite magnet and related introduction

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.

brief introduction

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.

Historical evolution

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.

According to the different magnetic properties and applications, ferrite can be divided into five types: soft magnetic, permanent magnetic, rotating magnetic, moment magnetic and piezomagnetic.
1、 Soft magnetic materials
These materials are easy to magnetize and demagnetize under weak magnetic field, such as zinc chromium ferrite and nickel zinc ferrite. Soft ferrite is a kind of ferrite material with wide application, many varieties, large quantity and high output value. It is mainly used for various inductive components, such as filter core, transformer core, wireless electromagnetic core, tape recording and video recording head, etc. it is also the key material of magnetic recording components.
2、 A compound with hexagonal structure and uniaxial anisotropy. They are mainly barium, strontium and lead ferrites and their composite solid solutions. It can be divided into the same magnetic field and the different magnetic field. This kind of ferrite material can be used to generate a stable magnetic field in the outer space because it can retain a strong constant remanence for a long time after the external magnetic field disappears. It is widely used, such as: in all kinds of meters, generators, telephones, speakers, TV sets and microwave devices as a permanent magnet.
3、 Hard magnetic material
Ferrite hard magnetic material is not easy to demagnetize after magnetization, so it is also called permanent magnetic material or constant magnetic material. Such as barium ferrite, steel ferrite, etc. It is mainly used in recorder, pickup, loudspeaker and magnetic core of various instruments in telecommunication devices.
4、 Gyromagnetic material
The gyromagnetism of magnetic materials refers to the phenomenon that under the action of two mutually perpendicular stable magnetic fields and electromagnetic wave magnetic fields, the plane polarized electromagnetic wave propagates in a certain direction inside the material, but its polarization plane will continue to rotate around the propagation direction. Although metal and alloy materials also have certain gyromagnetism, due to low resistivity and large eddy current loss, the electromagnetic wave can not go deep into them, so it can not be used. Therefore, the application of ferromagnetic materials has become a unique field of ferrite. Gyromagnetic materials are mostly used in microwave devices, such as waveguides or transmission lines. It is mainly used in radar, communication, navigation, telemetry and other electronic equipment.
5、 Rectangular magnetic material
This refers to ferrite materials with rectangular hysteresis loops. Its characteristic is that when there is a small external magnetic field, it can be magnetized and saturated. After removing the external magnetic field, the magnetism remains the same as when it is saturated. Such as magnesium manganese ferrite, lithium manganese ferrite and so on. This kind of ferrite material is mainly used in memory cores of various electronic computers.
6、 Piezomagnetic material
This kind of material refers to the ferrite material which is mechanically elongated or shortened in the direction of magnetic field during magnetization, such as nickel zinc ferrite, nickel copper ferrite and nickel chromium ferrite. Piezomagnetic materials are mainly used as transducers for mutual conversion of electromagnetic energy and mechanical energy, and as magnetostrictive elements for ultrasound.

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