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Permanent magnetic material

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permanent magnetic materials introduction, classification, development history

permanent magnetic materials are divided into aluminum nickel and cobalt permanent magnet alloy, iron chromium cobalt permanent magnetic alloys, permanent magnet ferrite, rare earth permanent magnet materials and composite permanent magnetic materials.

Permanent magnetic material introduction

Permanent magnetic material is a wide hysteresis loop, high coercive force, high remanence, once it is magnetized it can keep constant magnetic force, also known as hard magnetic materials. Practically, permanent magnet is working in the second quadrant demagnetization part of the hysteresis loop and deep magnetic saturation. The commonly used permanent magnet materials are divided into aluminum nickel and cobalt permanent magnet alloy, iron chromium cobalt permanent magnetic alloys, permanent magnet ferrite, rare earth permanent magnet materials and composite permanent magnetic materials.

1. Aluminum nickel and cobalt permanent magnetic alloys.

Iron, nickel, aluminum as the main component, also contains the elements such as copper, cobalt, titanium with high remanence and low temperature coefficient, magnetic stability. There are  two kinds of alloy casting and powder sintering alloy. It is widely used in 1930 ~ 1960s, now mainly used in the instrument, meter, micro motors, relays, etc.

2. Iron chromium cobalt permanent magnetic alloys 

With iron, chromium, cobalt element as the main ingredient, also contain molybdenum and a small amount of titanium, silicon. The processing performance is good, can be cold thermoplastic deformation. Its magnetic property is similar to aluminum nickel and cobalt permanent magnet alloy, and can improve the magnetic performance through plastic deformation and heat treatment. Used in the manufacture of all kinds of small cross section, complex shape of small magnet components.

3. Permanent magnetic ferrite

Mainly include barium ferrite, strontium ferrite, and it has high resistivity, big coercive force, can be effectively applied in the air gap magnetic circuit, especially suitable for small generator and permanent magnet motors. Permanent magnetic ferrite do not contain precious metals such as nickel, cobalt, has rich source of raw materials, simple process, low cost, can replace aluminum nickel and cobalt permanent magnet in system of magnetic separator, magnetic bearing, speakers, microwave devices, etc. But the maximum magnetic energy is low, temperature stability is low, quality of a material is brittle, fragile, low resistance to impact and vibration, unfavorable for measuring instrument and precision requirements of the magnetic device.

4. Rare earth permanent magnet materials

Mainly include Cobalt rare earth permanent magnet materials and ndfeb permanent magnet materials. The former is a rare earth element cerium, praseodymium, lanthanum, neodymium and cobalt formation of intermetallic compounds, its magnetic energy can be up to 150 times that of carbon steel, 3 ~ 5 times of aluminum nickel and cobalt permanent magnet, 8 ~ 10 times of permanent magnet ferrite, low temperature coefficient, stable magnetic performance, coercive force up to 800000 / m. It is mainly used for low speed torque motors, start motors, sensors, magnetic system of magnetic bearing, etc. Ndfeb permanent magnet material is the third generation of rare earth permanent magnet materials, the remanence, coercive force and the maximum magnetic energy higher than the former, less fragile, has good mechanical properties, alloy density is low, is advantageous to the magnetic components of light-duty, thin, small and microminiaturization. But its magnetic temperature coefficiency is high which limit its application.

5. Composite permanent magnetic materials

made from permanent magnetic material and powder compounded plastic material as a binder. Due to its certain percentage of binder content, so the magnetic than corresponding no binder magnetic materials significantly reduced. In addition to the metal composite permanent magnetic materials, other composite permanent magnetic materials due to the binder and the limit of the heat resistance, temperature is low, generally less than 150 ℃. But composite permanent magnetic materials high dimensional accuracy, good mechanical performance, magnet performance uniformity is good, the parts easy to radial orientation and multi-polar magnet magnetization. Mainly used in the manufacture of instruments and meters, communication equipment, rotating machinery, such as magnetic therapy equipment and sporting goods.

Permanent magnetic material --Classification

The first major categories: permanent magnet alloy materials, including rare earth permanent magnet (ndfeb Nd2Fe14B), samarium cobalt (SmCo), aluminum nickel and cobalt (AlNiCo) 

The second major category is: Ferrite permanent magnet (Ferrite) 

According to different production process it can be divided into: sintered ferrite, bonded ferrite, plastic injection ferrite, furthermore, on the basis of the three process, as per the magnetic crystal orientation it can be  divided into isotropic and anisotropic magnets.

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