Magnetic Materials Series Report Overview – 1
Overview of Magnetic Materials
Magnetic materials are the third-level sub-category industry of special metal functional materials in the overall industry of new materials
magnetism of matter Magnetic Materials Overview
Magnetism is the effect of magnetic force on a substance placed in a non-uniform magnetic field. Any substance can be more or less magnetized in an external magnetic field, but the degree of magnetization is different. According to the properties of substances in external magnetic fields, substances can be divided into five categories: paramagnetic substances, diamagnetic substances, ferromagnetic substances, ferrimagnetic substances, and antiferromagnetic substances:
1. Paramagnetic material: When the material is close to the magnetic field, it can be magnetized according to the direction of the magnetic field, but the degree of magnetization is quite weak, which requires precision instruments to measure. If the material loses the external magnetic field, the internal magnetic field will also return to zero, that is, it will no longer be magnetized. Such as aluminum, oxygen, etc.
2. Diamagnetic substance: a substance with a negative magnetic susceptibility. When subjected to an external magnetic field, an induced electron circulation is generated in the molecule, and the magnetic moment generated by it is opposite to the direction of the external magnetic field, that is, the direction of the magnetic field after magnetization is the same as the direction of the external magnetic field. on the contrary. All organic compounds are diamagnetic, graphite, lead, water, etc. are diamagnetic substances.
3. Ferromagnetic substances: After being magnetized under the action of an external magnetic field, even if the external magnetic field disappears, it can still maintain its magnetized state.
4. Ferrimagnetic material: The macroscopic magnetism is the same as that of ferromagnetic material, and the relative magnetic susceptibility is low. The typical ferrimagnetic material is ferrite. The most significant difference between ferrimagnetic substances and ferromagnetic substances is the internal magnetic structure.
5. Antiferromagnetic substances: Inside antiferromagnetic substances, the spins of adjacent valence electrons tend to be in opposite directions. This substance has a net magnetic moment of zero and produces no magnetic field. This material is relatively uncommon, and most antiferromagnetic materials exist only at low temperatures. If the temperature exceeds a certain threshold, it usually becomes paramagnetic. For example, chromium, manganese, etc. are all antiferromagnetic.
Most materials are diamagnetic or paramagnetic, and they respond weakly to external magnetic fields. Ferromagnetic substances and ferrimagnetic substances are ferromagnetic substances, and the so-called magnetic materials usually refer to ferromagnetic materials. Ferromagnetic materials are generally iron Fe, cobalt Co, nickel and Ni elements and their alloys, rare earth elements and their alloys, and some compounds of manganese and Mn.
Common magnetic performance parameters
Coercive force Hc: It is a quantity indicating the difficulty of magnetization of a material, and depends on the composition and defects (impurities, stress, etc.) of the material.
The maximum magnetic energy product BH: refers to the product of the magnet Bm and Hm. The larger the magnetic energy product, the less magnetic material is required to produce the same effect.
Curie temperature Tc: The magnetization of ferromagnetic substances decreases as the temperature increases. When a certain temperature is reached, the spontaneous magnetization disappears and becomes paramagnetic. The critical temperature is the Curie temperature. It determines the upper temperature limit for the operation of magnetic devices.
Magnetic material classification and development history
Magnetic material classification
Magnetic materials can be divided into soft magnetic materials and hard magnetic materials according to the difficulty of demagnetization after magnetization.
Soft magnetic material: The maximum magnetization can be achieved with the minimum external magnetic field, and it is a magnetic material with low coercivity and high permeability. Soft magnetic materials are easy to magnetize and also easy to demagnetize.
Hard magnetic material: also known as permanent magnet material, refers to the material that is difficult to magnetize and difficult to demagnetize once magnetized. Its main feature is high coercivity, including rare earth permanent magnet materials, metal permanent magnet materials and permanent magnet ferrites .
-Classification of common magnetic materials-
magnetism of matter Magnetic Materials Overview
In general, permanent magnet materials are commonly understood as magnets. The initial discovery came from natural permanent magnets in nature. After Maxwell, Tesla and other physical scientists laid the foundation of electromagnetism, academia began to pay attention to and study permanent magnet materials. The general permanent magnet materials studied in the early stage are mainly AlNiCo and ferrite. Due to the development of science and technology and the expansion of industrial use, the general permanent magnets such as AlNiCo and ferrite can no longer meet the application and use requirements. With the deepening of scientific research understanding and the improvement of rare earth element smelting and application technology, rare earth permanent magnet materials have emerged with the vigorous development of economy and industry due to their excellent performance. The two main materials represented are samarium cobalt and NdFeB rare earth permanent magnet material.
The research and industrial applications of magnetic materials have developed over time as follows:
The first generation of rare earth permanent magnet 1:5 type samarium cobalt SmCo5 material came out in 1967, its maximum magnetic energy product (BH) 5.1-20MGOe, coercivity Hc=17.09KOS.
The second-generation rare earth permanent magnet 2:17 type samarium cobalt Sm2Co17 material came out in 1972, the maximum magnetic energy product reached 15-35MGOe, and the coercivity Hc=10.05KOS.
The development of the previous two generations of permanent magnet materials was limited due to the scarcity and high price of samarium cobalt raw materials. The third-generation rare earth permanent magnet was updated to NdFeB rare earth element-based material in 1983, which was developed by General Electric GE Company in Japan Sumitomo Company, and the magnetic energy product reached 25-38MGOe.
Later, with the development and iteration of technology, the maximum magnetic energy product of NdFeB permanent magnets from Neomax Corporation of Japan reached an astonishing 59.5MGOe. This magnet is the second most magnetic permanent magnet after absolute zero holmium magnets today.
The most prominent point of samarium cobalt rare earth material is that it can work at a temperature of 300 degrees, and the Curie temperature is as high as 700 degrees, but the material is brittle as a whole, and attracting and impacting the magnet may cause the magnet to smash. The NdFeB material has excellent magnetic strength and high coercivity. The structure is stable and not easy to break. Its maximum operating temperature is 180 degrees, when the temperature reaches 150 degrees, 5% demagnetization will occur, and the Curie temperature is around 300 degrees.
Permanent magnet materials are widely used in electronics, general machinery, automobiles and transportation industries. Common products include: motors, electronic components, etc. Under the condition of general use temperature (<200 degrees), new energy vehicles driven by NdFeB permanent magnet motors have spread all over the country. At the same time, NdFeB permanent magnet materials are widely used in general machinery, such as air compressors, centrifugal pumps and other rotating machinery. When the operating temperature exceeds 200 degrees and the working temperature conditions are harsh, such as key high temperature scenarios such as mines and smelters, samarium cobalt materials can well exert their high Curie temperature characteristics.
The third generation of rare earth permanent magnets
NdFeB permanent magnet Magnetic Materials Overview
NdFeB permanent magnet material is the representative of rare earth permanent magnet material. According to different production processes, it can be divided into three types: sintering, bonding and hot pressing. Sintered NdFeB is the rare earth permanent magnet material with the highest output and the most extensive application.
After the successful development of NdFeB in 1983, my country followed the developed countries and quickly realized industrialization. Sanhuan Company of the Chinese Academy of Sciences has purchased the patents of General Electric and Sumitomo Corporation of Japan, and has become the leading company of permanent magnet materials in China, leading my country in the leading position of rare earth permanent magnet industry and performance. my country is rich in rare earth elements and has a monopoly in the world industrial chain. China’s current status is inseparable from the development and price advantage of NdFeB industry.
NdFeB permanent magnet application field
NdFeB permanent magnets are the most powerful permanent magnet materials in contemporary magnets. Its maximum magnetic energy product is 5-12 times that of ferrite magnets and 3-10 times that of AlNiCo magnets; its coercivity is equivalent to 5-10 times that of ferrite magnets and 5 times that of AlNiCo magnets. -15 times, its potential magnetic performance is extremely high, and it can absorb heavy objects equivalent to 640 times its own weight.
The main raw material iron of NdFeB permanent magnet material is very cheap, and the reserve of rare earth neodymium is 10-16 times more than that of samarium, so its preparation cost is much lower than that of samarium cobalt permanent magnet. The mechanical properties of NdFeB magnets are better than those of samarium cobalt magnets and alnico magnets, and they are easier to cut and drill and process complex shapes. The disadvantage is that the temperature performance of NdFeB is poor, and it has a large demagnetization when used at high temperatures, and the Curie temperature is lower than that of samarium cobalt permanent magnets. In summary, the application fields of NdFeB permanent magnet materials are quite extensive