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Humans have been using magnetic materials long before.

People in the spring and autumn period and the warring states period have discovered the iron and guide sex of natural magnet.

Modern humans divide magnetic materials into permanent magnet materials, soft magnetic materials, magnetic recording materials and magnetic materials with special functions.

1. Permanent magnet material

The common permanent magnet materials include aluminum nickel cobalt alloy, ferrite permanent magnet material and rare earth permanent magnet material.

Aluminum nickel and cobalt alloy is made by aluminum and nickel alloy development, at present our country can make the aluminum nickel and cobalt alloy models are mainly LNG34, LNG52, LNGJ32, LNGJ56, etc.

Due to the main characteristics of aluminum nickel and cobalt is high Br (residual magnetic induction intensity), low coercive force of permanent magnet materials, the relative permeability in 3 above, so in the specific application, its magnetic poles must do grow cylinder or long rod, to minimize the magnetic field effect.

Alnico magnet coercive force itself is low, so should be strictly prohibited in the process of using any iron contact aluminum nickel and cobalt permanent magnet material, in order to avoid causing permanent magnet demagnetization local distortion and magnetic flux distribution in the magnetic circuit.

The advantages of the aluminum nickel cobalt magnet are that the temperature coefficient is small, and the degradation of the permanent magnetism due to temperature change is small, but the material is hard and brittle and difficult to process.

The main applications of nickel and cobalt are in electronic ignition systems, electric meters, voltammeters, medical instruments, industrial motors, magnetic reed switches, generators, hand tools, vending machines, etc. Ferrite permanent-magnet material is one of the most widely used permanent-magnet materials, and its main component is MoFe2O3.

It has the advantages of high coercive force, light weight, abundant raw materials, cheap price, oxidation resistance, corrosion resistance, large anisotropic constant of magnetic crystal, and the approximate line of demagnetization curve.

The disadvantage is that the residual magnetism is low and the temperature coefficient is large and fragile.

The retentive force of ferrite permanent-magnet material lies between the material of aluminum nickel cobalt alloy and the rare earth cobalt permanent magnet material. Due to its low residual magnetism, it is generally suitable for the design of flat shape.

Due to its low cost, ferrite magnets have wide application fields, ranging from motors and loudspeakers to toys and crafts, and are currently the most widely used permanent magnet materials.

Rare earth permanent-magnet materials are highly coercive; Maximum magnetic energy accumulation; Reversible permeability is one advantage.

Therefore, its magnetic properties can exceed the ferrite and aluminum and cobalt and other magnetic materials.

The emergence of rare earth permanent magnet material makes the permanent magnet synchronous motor with light weight and small volume come into being, thus expanding the application range of permanent magnet synchronous motor.

Rare earth cobalt permanent-magnet material has excellent performance, but the price is higher, so the design must be careful to use the smallest volume to achieve the desired effect.

Due to the high resistance of rare earth cobalt permanent magnet materials, it can be used as a sheet of permanent magnetic material to reduce volume and save materials. Common rare earth magnets include SmPrCo, SmCoPeCo, SmPrNdCo, CeCoCuFe, Sm2Co17, etc.

2. Soft magnetic material

The soft magnetic material can be divided into nine categories according to its composition.

(1) pure iron and low carbon steel. The carbon content is less than 0.04%, including electromagnetic pure iron, electrolytic iron and carbonyl iron. It is characterized by high saturation magnetization, low price and good processing performance. However, it has low resistivity and large eddy current loss under alternating magnetic field. It is only suitable for static use, such as manufacturing electromagnetic core, pole boots, relay and speaker magnetic conductor, magnetic shield and so on.

(2) ferrosilicon alloy. The silicon content is 0.5% ~ 4.8%. It is commonly used in thin plate, commonly known as silicon steel sheet. After adding silicon to pure iron, the magnetic material can be eliminated with the use of time. Reduced with the increase of silicon content, thermal conductivity, brittleness increases, the saturation magnetization intensity decreased, but its high resistivity and magnetic conductivity, coercive force and eddy current loss is reduced, which can be used in the field of communication, make motor iron core, transformers, relays, transformers, etc. (3) ferroaluminum alloy. Aluminum containing 6% ~ 16%, and has a good soft magnetic properties, permeability and high resistivity, high hardness, good wear resistance, but brittle, mainly used in the manufacture of small transformers, relays, magnetic amplifier of iron core and magnetic head, ultrasonic transducer, etc.

(4) ferrosilicon aluminum alloy. Add silicon to the binary iron alloy. Its hardness, saturation magnetic induction, magnetic conductivity and resistivity are high. The disadvantage is that magnetism can be sensitive to the fluctuation of composition, brittle and poor machining performance. Mainly used for audio and video heads.

(5) nickel-iron alloy. The nickel content is 30 % ~ 90%, and is also called the permalloy alloy. The magnetic energy can be controlled by the alloying element ratio and the appropriate process, and the magnetic materials can be obtained with high permeability, constant magnetic conductivity and moment magnet. Its plasticity is high, the stress is sensitive, can be used as pulse transformer material, inductance core and functional magnetic material.

(6) ferrocobalt alloy. Cobalt content is 27% ~ 50%. High saturation magnetization and low resistivity. Suitable for making pole boots, motor rotor and stator, small transformer core, etc.

(7) soft ferrite. Nonmetallic ferrous magnetic soft magnetic material. High resistivity (10-2 ~ 1010 Ω m.), saturation magnetization, lower than the metal price is low, widely used as the inductive components and transformer components (see ferrite).

(8) amorphous soft magnetic alloy. A non - long-duration, amorphous alloy, or metallic glass, or amorphous metal. Its magnetic conductivity and resistivity are high, with little coercive force and no sensitivity to stress. There is no anisotropy of magnetic crystals caused by crystal structure, which has the characteristics of corrosion resistance and high strength. In addition, its Curie point is much lower than the crystalline soft magnetic material, and the power loss is greatly reduced. It is a new kind of soft magnetic material which is being developed and utilized.

(9) super microcrystalline soft magnetic alloy. A soft magnetic material discovered in the 1980s. Consists of less than 50 nanometers in crystal phase and amorphous phase composition of grain boundary, has better comprehensive performance than crystalline and amorphous alloy, not only high magnetic permeability, low coercive force, low iron loss, and saturated magnetic induction intensity is high, the stability is good. The main research is the iron base super microcrystalline alloy.

Magnetic recording materials

Magnetic material used to input (write), record, store and output (read) sounds, images, Numbers and other information using magnetic properties and magnetic effects.

It is divided into magnetic recording medium material and magnetic head material. The former mainly completes the information recording and storage function, the latter mainly completes the information write and read function.

In 1898, a Danish engineer, Ponlsen, invented the recording telephone by recording the sound with magnetic wires.

Hard disk technology and magnetic recording techniques for storing electronic computer data were developed in the 1950s. The development and application of magnetic tape camera in the 1980s is another development of magnetic recording technology.