Humans have been using magnetic materials for a long time.

People in the spring and autumn period and the warring states period have discovered the iron absorption and guidance of natural magnets.

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

Permanent magnet material

The common permanent magnet materials are al-ni-co alloy ferrite permanent magnet and rare earth permanent magnet.

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.

As the main characteristics of alnico are the permanent magnet materials with high Br (residual magnetic induction intensity) and low coercient force, their relative permeability is above 3, so in the specific application, their magnetic poles must be grown columns or long bars to minimize the demagnetization effect.

The aluminum-nickel-cobalt magnet itself has a low coercing force, so it should be strictly forbidden for any iron to contact the aluminum-nickel-cobalt permanent magnet in the process of use, so as to avoid local demagnetization of permanent magnet and distortion of flux distribution in the magnetic circuit.

The advantages of al-ni-co magnets are that the temperature coefficient is small, and the degradation of permanent magnet characteristics due to temperature change is small, but the material is hard and brittle, and difficult to process.

Alnico is mainly used in electronic ignition systems, electricity meters, volt-ammeters, medical instruments, industrial motors, magnetic reed switches, generators, hand tools, vending machines and other fields.
Ferrite permanent magnet material is one of the most widely used permanent magnet materials. Its main component is MoFe2O3.

With strong coercing force, light weight, rich source of raw materials, cheap price, oxidation resistance, corrosion resistance, magnetic crystal anisotropy constant is large, demagnetization curve is approximately straight line and other advantages.

The disadvantage is low remanence, high temperature coefficient, fragile.

The coercivity of ferrite permanent magnet material is between al-ni-co alloy material and rare-earth cobalt permanent magnet material. Due to its low residual magnetism, it is generally suitable for flat design.

Because of its low cost, ferrite magnets have a wide range of applications, from motors and speakers to toys and crafts, making them the most widely used permanent magnet materials at present.

Rare earth permanent magnet materials have high coercivity.
The maximum magnetic energy product is large;
Reversible permeability equals one.

As a result, it is far more magnetic than ferrite and other magnetic materials such as alnico.

The appearance of rare earth permanent magnet material makes the light weight and small size permanent magnet synchronous motor come out one after another, thus expanding the application range of permanent magnet synchronous motor.

Rare earth cobalt permanent magnet material has excellent performance, but its price is relatively high, so it must be carefully calculated in the design to achieve the expected effect with the smallest volume.

Due to its strong coercivity, rare earth cobalt permanent magnet can be made into thin sheet permanent magnet to reduce volume and save materials.
The common rare earth permanent magnet materials are SmPrCo, SmCoPeCo, SmPrNdCo, CeCoCuFe, Sm2Co17 and so on.

Soft magnetic materials

Soft magnetic materials can be divided into nine categories according to the composition, the following sequence of characteristics.

(1) pure iron and mild steel.
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, its low resistivity, large eddy current loss in the alternating magnetic field, only suitable for static use, such as the manufacture of electromagnetic core, pole boots, relays and speaker magnetic conductor, magnetic shield, etc.

(2) ferrosilicon alloy.
Silicon content of 0.5% ~ 4.8%, generally made into the use of thin plate, commonly known as silicon steel sheet.
The addition of silicon to pure iron can eliminate the phenomenon that the magnetism of magnetic materials changes with the service time.
With the increase of silicon content, thermal conductivity decreases, brittleness increases, saturation magnetization decreases, but its resistivity and permeability are high, and the forced force and eddy current loss decrease, which can be applied to the field of ac, making the iron core of motor, transformer, relay, transformer and so on.
(3) iron - aluminum alloy.
Aluminum 6% ~ 16%, with good soft magnetic performance, high permeability and resistivity, high hardness, good wear resistance, but brittle, mainly used in the manufacture of small transformers, magnetic amplifiers, relays, such as the iron core and magnetic head, ultrasonic transducers.

(4) fe-si-al alloy.
Silicon was added into binary fe - al alloy.
Its hardness, saturation magnetic induction intensity, permeability and resistivity are high.
The disadvantage is that the magnetic property to the component fluctuation sensitivity, brittleness, poor processing performance.
Mainly used for audio and BBB 0 head.

(5) nickel-iron alloy.
Nickel content of 30% ~ 90%, also known as permo alloy, through alloying element ratio and appropriate process, can control magnetic properties, obtain high permeability, constant permeability, magnetic moment and other soft magnetic materials.
Its high plasticity, more sensitive to stress, can be used as pulse transformer material, inductance core and functional magnetic material.

(6) iron cobalt alloy.
Cobalt content 27% ~ 50%.
It has high saturation magnetization and low resistivity.
Suitable for manufacturing pole boots, motor rotor and stator, small transformer core, etc.

(7) soft ferrite.
Non-metallic ferrous magnetic soft magnetic materials.
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.
An alloy without long range order and without grain, also known as metallic glass, or amorphous metal.
It is characterized by high permeability and resistivity, low coercivity, little sensitivity to stress, no magnetic anisotropy caused by crystal structure, corrosion resistance and high strength.
In addition, the Curie point is much lower than that of crystalline soft magnetic material, and the power loss is greatly reduced.

(9) ultracrystalline soft magnetic alloy.
A soft magnetic material discovered in the 1980s.
It is composed of crystalline phase and amorphous grain boundary phase less than 50 nanometers. It has better comprehensive performance than crystalline and amorphous alloy, not only with high permeability, low coercivity and small iron loss, but also with high saturation magnetic induction intensity and good stability.
Now the main research is iron - based ultrafine alloy.

Magnetic recording materials

Magnetic material that USES magnetic properties and effects to input (write), record, store, and output (read) information such as sound, images, figures, etc.

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

In 1898, Ponlsen, a Danish engineer, invented the recording telephone by recording sound magnetically on magnetic steel wire.

In 1950s, hard disk technology and magnetic recording technology were developed to store computer data.
The development and application of magnetic tape camera in 1980s is a new development of magnetic recording technology.

Magnetic materials with special functions

(1) magnetoelastic materials.
Under the action of the magnetic field, the shape of this magnetic material changes, which can be expressed as elongation or shortening in length, expansion and contraction in volume.

(2) magnetoresistive materials.
The resistance of this magnetic material changes under the action of a magnetic field.

(3) magnetic refrigeration materials.
Magnetic refrigeration is a kind of magnetic material as the working medium of refrigeration technology, the basic principle is the magnetic effect (magneto caloriceffect) magnetic refrigeration material isothermal magnetization to the outside world to release heat, and isothermal demagnetization from the outside world to absorb heat, in order to achieve the purpose of refrigeration.
The advantage of this material is environmental friendly, no environmental pollution and damage;
High efficiency and energy saving, carnot cycle efficiency can reach 60~ 70%;
Stable and reliable.

(4) magnetic fluid.
Also known as magnetic fluid or iron fluid.
It is a liquid magnetic material which is sensitive to magnetic field and can flow.
In this method, ferromagnetic particles (< 10nm) mixed into carrier fluid are evenly dispersed with dispersant to form a kind of fluid suspended colloidal liquid.

This liquid has the property of being attracted by magnets without settling and agglutinating under normal centrifugal and magnetic forces.

The magnetic fluid produced by nano metal and alloy powder has excellent performance, which can be widely used in the fields of sealing shock absorption, medical equipment, sound regulation and light display.

Magnetic material is an important basic functional material of electronic industry, which is widely used in computer, electronic devices, communication, automobile, aerospace and other industrial fields, and household appliances, children's toys and other daily necessities. With the rapid development of world economy and science and technology, magnetic materials will have unprecedented demand.

Magnetic materials play an important role in traditional and emerging fields such as electronics, computers, information communication, medical treatment, aerospace, automobiles, wind power, environmental protection and energy conservation.
Magnetic material has become an irreplaceable material to promote the development of high and new technology and contemporary economic progress.

At present, the development of magnetic materials in China ranks first in the world.
China has become the world's largest producer of permanent magnet materials.
At present, China has become the center of the magnetic material industry in the world.
China's total output value of magnetic materials is about 26.5 billion yuan, and the output value of permanent magnet ferrite is 6.2 billion yuan, with an average price of 15,000 yuan per ton.
According to this calculation, the output value of ferrite raw material is about 1 billion yuan.

In recent years, due to the substantial increase of energy, raw materials and labor costs, the costs have risen, and enterprises in the industry have generally shown a decline in volume and profit.
In the future, the key to the development of domestic magnetic materials enterprises is still to further accelerate the industrial upgrading, improve the product structure, so as to further increase the added value of products.

With the further warming of the global economy, the application of magnetic materials in energy-saving motors, LCD TVS, 4G, wind power, digital products, Internet of things and new energy vehicles and other emerging fields will grow rapidly.