According to properties and uses, ferrites can be divided into soft magnetic, hard magnetic, gyromagnetic, moment magnetic, magnetic bubble, magneto-optical, piezoelectric and other ferrites. Below respectively introduction.
1. Soft ferrite
Soft ferrite is currently the most diverse and widely used magnetic material of various ferrites. It is characterized by high initial permeability, so that the volume of the coil with the same inductance requirement can be reduced, and the permeability the temperature coefficient should be small to adapt to temperature changes, and the coercive force should be small, so that it is easy to magnetize under a weak magnetic field, and it is also easy to demagnetize and lose magnetism. In addition, their specific loss factor is smaller and the resistivity is higher, so that the loss of the material is small, and it is suitable for use under high frequency.
Commonly used soft ferrites include spinel type ferrite, LiZn ferrite and magnetoplumbite type very high frequency ferrite, such as BaCO3, Fe2O3, etc. Soft ferrite is mainly used as various inductance components, such as antenna cores and filter cores.
2. Hard ferrite
Hard ferrite, also known as permanent ferrite or permanent ferrite, is a kind of ferrite that is not easy to demagnetize after magnetization and can retain magnetism for a long time. It is generally used as a source of constant magnetic field. They have the following characteristics: the residual magnetic induction intensity is relatively high, generally 0.3~
0. 5T; high coercivity, generally between 0.1 and 0.47; maximum magnetic energy product is high, generally between 8000~40000J/m3. Of course, as hard for magnetic materials, the larger the above three parameters, the better.
At present, most of the known hard ferrite materials are magnetoplumbite, mainly Ba ferrite (BaO·6Fe2O3), Sr ferrite body (SrO·6Fe2O3), Pb ferrite (PbO·6Fe2O3) and their composite ferrite. In addition, the anisotropic spinel structure Co ferrite (CoO·Fe2O3) can also be used as a hard magnetic material. Recently, it has been discovered that sintered pentacobalt samarium (SmCo5) has high magnetic properties, and its magnetic properties exceed those of ordinary hard magnets. 10 times the oxygen body.
3. Rotary ferrite
Rotary ferrite is also called microwave ferrite. Under the action of a high-frequency magnetic field, the plane-polarized electromagnetic wave in the ferrite presses a certain In the process of directional propagation, the plane of polarization will continuously rotate around the direction of propagation of a ferrite material. Widely used in the microwave field used to make microwave devices for radar, communications, television, surveying, satellites, missile systems, etc. Commonly used microwave gyromagnetic ferrites include spinel type and garnet type. The former is cheap and the latter has excellent performance. In addition, hexagonal ferrite can also be used in the millimeter wave band. In terms of material preparation, it is mainly divided into three categories: polycrystalline, single crystal, and thin film.
Spinel ferrite mainly includes Mg, Ni, Li and other ferrites, and AI and Cr are usually added to control the saturation magnetization. Plus Mn and Bi are used to increase the resistivity, and Cu and Bi are added as fluxes to increase the density. Li ferrite has a high Curie point and low magnetostriction Coefficient, large magnetic anisotropy, narrow ferromagnetic resonance line and good rectangular hysteresis loop, the price is cheaper than garnet ferrite, and it is an excellent material for manufacturing high-power, low-temperature-coefficient lock-type devices. Li is volatile at high temperature, and Bi2O3 can be added to reduce burn temperature to obtain a fully sintered compact product.
Garnet-type gyro ferrites can now meet the needs of most devices in the microwave frequency range. Among them, yttrium iron garnet ferrite is used as a magnetic material for low-power devices in the microwave range, and its performance is very good, but the cost is relatively expensive. In order to meet the needs of various band devices , often replace Fe and Y ions with a variety of ions such as In, Sn, Gd, Ge, Zr, Ti, Al, Ca, and V to change the M value and improve high temperature stability. Commonly used garnet ferrites are Y-Al garnet series, Y-Ca-V garnet series, Y-Gd garnet series In the long-wavelength microwave range, Y-free garnet ferrite is often used. In order to increase the material density, control a certain grain size in order to prevent the generation of Fe2+ ions, increase the resistance, and reduce the dielectric loss, the hot pressing process is commonly used in the preparation of microwave ferrite. The sintering can usually be carried out in an oxygen atmosphere.