Ferrite magnets are ferromagnetic metallic oxides. In regard to the electrical characteristics, the resistivity of ferrite magnet is much higher than resistivity of metal and alloy magnetic material, and the ferrite have higher dielectric properties. It has superior magnetic conductivity in high frequency. Therefore, this magnets have become a widely used nonmetallic magnetic material in the field of weak electric and high frequency. Because the magnetism stored unit volume is low, saturated magnetized intensity is low. It limited the application of ferrite magnets in the field which request high energy density in low frequency with high voltage and high power.
This is suitable for high frequency electromagnetic device. According to the different magnetic properties and application, ferrite are classified six categories including ferrite permanent magnets, hard ferrite, flexible ferrite, rectangular magnetic loop ferrite, gyro-magnetic ferrite and piezo-magnetic ferrite. Because the production process and appearance looks like ceramics, ferrite is also called ceramic magnets.
1. Flexible ferrite magnets
Flexible ferrite magnets are easy to be magnetized and demagnetized in the relatively weak magnetic field, such as zinc chrome ferrite magnets and nickel zinc ferrite magnets etc. The flexible ferrite magnets are widely used in industry with many varieties, large quantity and high production value. It mainly used for various inductance components such as magnetic core of filters & transformer, radio magnetic core, tape recording and video head etc, and it is also the important materials for magnetic recording components.
2. Ferrite permanent magnets
Ferrite permanent magnets are compound with single axis anisotropic hexagon structure. It is made of barium, strontium, lead and the compound of interstitial. China Rare Earth Magnet Limited have isotropic and anisotropic ferrite magnets.
Because the ferrite permanent magnets are able to longtime keep strong constant residual magnetism after the outside magnetizing field disappears, then it can be used to produce constant magnetic field in outside space. The application as permanent magnet usage is very extensive, for example: in all kinds of electric meter, generators, telephone, speaker, television and microwave devices.
3. Hard ferrite magnets
Hard ferrite magnets are not easily demagnetized after magnetizing. Therefore, it is known as permanent magnetic material and constant magnetic materials, such as barium and steel ferrite magnets etc. It is mainly used for telecom device: the recording device, pick-up sets, speakers, magnetic core of various instruments.
4. Gyro-magnetic ferrite
Under the action of mutually perpendicular steady magnetic field and electromagnetic waves magnetic filed, the plane polarized electromagnetic wave spread with certain directionality in material internal, but the polarization plane will continue to roll around the spreading direction, which is expression of gyro-magnetic ferrite. Metal and alloy material also have gyro-magnetic property, but because of the low resistivity, huge loss of the eddy, the electromagnetic wave can't further enter inside, can not be used. Therefore, the application of gyro-magnetism is the exclusive filed of ferrite magnets. The gyro-magnetic ferrite is mostly combined with waveguide tube and transmission as various microwave devices which are used radar, communication, navigation, remote sensing and other electronic equipments.
5. Rectangular magnetic loop
It is rectangular hysteresis loop ferrite material. Its characteristic is that the weak external magnetic field can make magnetization and achieve saturation, even remove the magnetic field, the magnetic strength can keep same saturation level. Such as magnesium manganese ferrite magnet, lithium manganese ferrite magnets have the characteristics. Rectangular magnetic loop ferrite is widely used for kinds of electronic computer memory magnetic core.
6. Piezo-magnetic
It mechanically elongate or shorten along magnetization direction when it is magnetizing, such as nickel zinc ferrite magnets, nickel copper ferrite magnets, nickel chrome ferrite and so on. Piezo-magnetic ferrite is widely used for transducer which is for mutual transformation of electromagnetic energy and mechanical energy, as magnetostriction components used for ultrasound.