Popularization of magnetic knowledge-Magnetism and magnetic materials

Popularization of magnetic knowledge-Magnetism and magnetic materials

Sintered NdFeB magnet, we all know it is called "magnet king", because the magnetism made of this rare earth material is the strongest in the world, so what other magnetic materials similar to NdFeB? What is the difference between different magnetic materials? How to judge which magnetic material should be used in my products? Next, we will have a comprehensive understanding of the magnetic material family through several articles.

Magnetism and magnetic materials

Ferrite magnetic material

Samarium Cobalt Permanent Magnetic Material

Other magnetic materials

Performance comparison of various magnetic materials

When it comes to magnetic materials, we have to talk about "magnetism" first. Experiments show that any substance can be magnetized more or less in an external magnetic field, but the degree of magnetization is different. According to the characteristics of substances in the external magnetic field, substances can be divided into five categories: paramagnetic substances, diamagnetic substances, ferromagnetic substances, ferrimagnetic substances, and antiferromagnetic substances:

Paramagnetic substance: It is a kind of substance that can be magnetized according to the direction of the magnetic field when they are moved closer to the magnetic field, but it is very weak and can only be measured with precision instruments; if the external magnetic field is removed, the internal magnetic field will also return to zero, resulting in It is not magnetic. Such as aluminum, oxygen, etc.

Diamagnetic substance: It is a substance with a negative magnetic susceptibility. When subjected to an external magnetic field, an induced electron circulation is generated in the molecule. 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 external magnetic field. The direction is opposite. All organic compounds are diamagnetic. Graphite, lead, water, etc. are all diamagnetic materials.

Ferromagnetic substance: 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 with magnetism. Iron, cobalt, and nickel are all ferromagnetic substances.

Ferrimagnetic material: The macroscopic magnetism is the same as ferromagnetism, but the magnetic susceptibility is lower. The typical ferrimagnetic material is ferrite. The most significant difference between them and ferromagnetic substances is the difference in internal magnetic structure.

Antiferromagnetic substance: Inside the antiferromagnetic substance, the spins of adjacent valence electrons tend to opposite directions. The net magnetic moment of this substance is zero and no magnetic field is generated. This kind of substance is relatively uncommon, and most antiferromagnetic substances only exist in low temperature conditions. If the temperature exceeds a certain value, it will usually become paramagnetic. For example, chromium, manganese, etc. have antiferromagnetic properties.

We call paramagnetic materials and diamagnetic materials weakly magnetic materials, and call ferromagnetic materials and ferrimagnetic materials strong magnetic materials. Generally speaking, magnetic materials generally refer to ferromagnetic substances. Magnetic materials are classified according to their use and can be divided into:

Soft magnetic material: The maximum magnetization can be achieved with the smallest external magnetic field. It is a magnetic material with low coercivity and high permeability. Soft magnetic materials are easy to magnetize and also easy to demagnetize. For example: soft ferrite, amorphous nanocrystalline alloy.

Hard magnetic materials: also called permanent magnetic materials, which refer to materials that are difficult to magnetize and are difficult to demagnetize once magnetized. Its main feature is high coercivity, including rare earth permanent magnetic materials, metal permanent magnetic materials and permanent ferrites .

Functional magnetic materials: mainly magnetostrictive materials, magnetic recording materials, magnetoresistance materials, magnetic bubble materials, magneto-optical materials, and magnetic thin film materials.

neodymium magnet