A material that can react in some way to a magnetic field is called a magnetic material. According to the magnetic field intensity of the material in the external magnetic field, it can be divided into diamagnetism, paramagnetism, ferromagnetism, antiferromagnetism and ferrimagnetism. Most materials are diamagnetic or paramagnetic, and they have a weak response to the external magnetic field. For magnetic materials, magnetization curves and hysteresis loops are characteristic curves that reflect their basic magnetic properties. Ferromagnetic materials are generally Fe, Co, Ni elements and their alloys, rare earth elements and their alloys, and some Mn compounds. According to the degree of difficulty of magnetization, magnetic materials are generally divided into soft magnetic materials and hard magnetic materials.
- Soft magnetic materials: (1) alloy strip or sheet: FeNi (Mo), FeSi, FeAl, etc. (2) amorphous alloy ribbons: Fe-based, Co-based, FeNi-based or FeNiCo-based with appropriate Si, B, P and other doping elements, also known as magnetic glass. (3) the magnetic media (iron powder core): FeNi (Mo), FeSiAl, carbonyl iron and ferrite, etc.) are coated and bonded by electrical insulating medium and pressed according to the requirements. (4)Ferrite: including spinel-type perovskite M O·Fe2O3 (M represents NiZn, MnZn, MgZn, CaZn, etc.) and magnetolead type perovskite Ba3Me2Fe24O41 (Me represents Co, Ni, Mg, Zn, Cu and its composite components). Soft magnetic materials are widely used in magnetic antennas, inductors, transformers, magnetic heads, headphones, relays, vibrators, TV deflection yoke, cables, delay lines, sensors, microwave absorption materials, electromagnets, accelerator high frequency acceleration cavities, magnetic field probes, magnetic substrates, magnetic field shielding, high frequency quenching energy accumulation, electromagnetic suckers, magnetic sensors (such as magnetocaloric materials as switches), etc.
- Gyromagnetic material: With unique microwave magnetism, the designed devices are mainly used for microwave energy transmission and conversion, including isolators, circulators, filters, and developing magnetic surface wave and magnetostatic wave devices (microwave ferrite devices). The commonly used gyromagnetic materials are ferrite materials such as Ni system, Mg system, Li system, YIG system and BiCaV system. Different structures and shapes such as single crystal, polycrystal, amorphous or thin film can be made according to the needs of the device.
- Permanent magnet materials: The commonly used permanent magnet materials are divided into (1)Al-Ni-Co permanent magnet alloys: cobalt, nickel, aluminum as the main composition, but also contains copper, titanium and other elements. It has high remanence and low temperature coefficient, and is magnetically stable. Now it is mainly used in the manufacture of magnetoelectric instruments, flow meters, micro-special motors, relays and so on. (2) Fe-Cr-Co permanent magnet alloy: it is mainly composed of iron, chromium and cobalt, but also contains molybdenum and a small amount of titanium and silicon. It has good processability and can be deformed by cold and hot plastics. its magnetic properties are similar to those of Al-Ni-Co permanent magnet alloys, and the magnetic properties can be improved by plastic deformation and heat treatment. It is used to manufacture all kinds of small magnet elements with small cross section and complex shape. (3) permanent magnet ferrite: mainly barium ferrite and strontium ferrite, which has high resistivity and high coercivity, can be effectively used in large air gap magnetic circuit, especially suitable for permanent magnet of small generator and motor. (4) rare earth permanent magnetic materials: mainly rare earth cobalt permanent magnetic materials and NdFeB permanent magnetic materials. (5) Composite permanent magnet material: it is composed of permanent magnetic material powder and plastic material as binder. Mainly used in the manufacture of instruments, communication equipment, rotating machinery, magnetic therapy equipment and sporting goods and so on.
Figure 1. Magnetic materials
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