Introduction of five common permanent magnet materials and their advantages and disadvantages

Permanent magnet material of aluminum nickel cobalt

Alnico permanent magnet materials were developed in 1930s. At that time, it had the best magnetic properties and low temperature coefficient, so it was widely used. After the 1960s, with the advent of ferrite permanent magnet and rare earth permanent magnet, aluminum nickel cobalt permanent magnet has been gradually replaced. At present, in the use of motor, it is only used on individual motor for detection, such as speed measuring generator.
Advantage:

  • 1. the magnetic properties of casting mould are high, and the process of powder sintering is simple, and it can be pressed into the required shape directly.
  • 2. the small temperature coefficient means that the magnetic energy changes very little with the change of temperature. The products with high temperature stability requirements are still a good choice.

Disadvantages:

  • 1. the coercive force is low, so it should be avoided from contacting any magnetic guide material in the process of use to avoid the irreversible demagnetization or magnetic flux distribution deformity in the local area.
  • 2. hard and brittle, poor processing performance.

Ferrite permanent magnet

Ferrite permanent magnet materials belong to non-metallic permanent magnet materials. In the use of motors, barium ferrite (Bao · 6fe2o3) and strontium ferrite (SRO · Fe2O3) are commonly used.
Advantage:

  • 1. high cost performance, excluding rare earth elements, cobalt, nickel and other precious metals;
  • 2. the manufacturing process is simple;
  • 3. the coercive force is large and the anti demagnetization ability is strong;
  • 4. a large part of demagnetization curve is close to a straight line. The recovery line basically coincides with the straight part of demagnetization curve, so it can be widely used without the need of stabilizing magnetism.

Disadvantages:

  • 1. the residual magnetic density is not high and the maximum magnetic energy product is not high, so the cross-sectional area of the magnetic flux is needed to be increased, which will lead to the larger volume of the motor;
  • 2. the influence of ambient temperature on magnetic properties is great. Therefore, it is necessary to check and calculate the minimum temperature and maximum demagnetization working point in use to prevent irreversible demagnetization at low temperature;
  • 3. hard and brittle, and cannot be processed by electricity.

Rare earth cobalt permanent magnet material

Rare earth cobalt permanent magnet materials are the excellent permanent magnetic materials which have excellent magnetic properties which have been developed in the mid-1960s.
Advantage:

  • 1. the residual magnetic induction strength and the maximum magnetic energy product are very high, among which the residual magnetic induction strength can be close to the level of Al Ni Co material, and the coercive force of magnetic induction is about 3 times that of ferrite permanent magnet;
  • 2. demagnetization curve is basically a straight line, and the recovery line basically coincides with demagnetization curve, and has strong anti demagnetization ability;
  • 3. Curie temperature is high, so the magnetic stability of this rare earth cobalt permanent magnet material is the best, which is suitable for manufacturing high performance permanent magnet motor.

Disadvantages:

  • 1. the price is expensive, so it is generally used only for military workers or special purposes;
  • 2. hard and brittle, and the tensile strength and bending strength are very low.

NdFeB permanent magnet

NdFeB permanent magnet material is a high performance permanent magnet material which was published in 1983.
Advantage:

  • 1. the magnetic energy is higher than that of rare earth cobalt permanent magnet, the residual magnetic induction strength, magnetic induction coercive force, and the maximum magnetic energy product are very high, which is the best permanent magnet with the magnetic property at present;
  • 2. high cost performance. Because the content of Neodymium in rare earth is more than ten times that of samarium, the price of iron and boron is very cheap, and there is no strategic material cobalt. This is why NdFeB has been widely used and popularized rapidly.

Disadvantages:

  • 1. curie temperature is low and temperature coefficient is high, so magnetic loss is large and thermal stability of magnetic energy is poor when used at high temperature;
  • 2. it is easy to rust because of its large amount of iron and neodymium.

Bonded permanent magnet material

It is necessary to note that the bonded permanent magnet material is not a specific component, but a composite permanent magnet material made by using the materials such as branch, plastic or low melting point alloy as adhesive, and mixing with the powder of permanent magnet uniformly, and then compressing, injecting or extrusion forming.
Advantage:

  • 1. the shape freedom is large, and it is easy to make the complex shape magnetic ring or thin-walled ring;
  • 2. if it is injection molding, it can also be embedded into other parts to form together;
  • 3. the size precision is high, it is not easy to deform, and it does not need to be processed twice to make high-precision magnet;
  • 4. high resistivity and easy to realize multipole magnetization;
  • 5. the performance is small in dispersion and high in qualification rate, and it is suitable for mass production;
  • 6. the machine has high strength and is not easy to break, and can be cut.

Disadvantages:
Because of the presence of adhesives, the magnetic properties are slightly poor.

In consumer products, ferrite permanent magnet, Nd-Fe-B permanent magnet and bonded permanent magnet materials are widely used. In short, ferrite is enough for general products. NdFeB is needed for high performance. In special cases, bonded permanent magnet materials may be used.

Source: China Permanent Magnet Manufacturer www.ymagnet.com

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