Basic knowledge of magnets
Overview of magnetic materials: Magnetism is one of the basic properties of matter. The phenomenon of magnetism is related to the movement of various forms of electric charge. Because the movement and spin of electrons inside the substance will produce a certain magnitude of magnetic field, magnetism is produced. All substances are magnetic. Nature can be divided into paramagnetic materials, diamagnetic materials, ferromagnetic materials, antiferromagnetic materials, and ferrimagnetic materials according to different magnetic properties. Among them, ferromagnetic materials and ferromagnetic materials belong to ferromagnetic materials. Such substances are collectively referred to as magnetic materials.
Classification, performance characteristics and uses of magnetic materials:
1 Ferrite magnetic material: generally refers to the conforming oxide of iron oxide and other metal oxides. Most of them are ferrimagnetic. Features: The resistivity is much higher than that of metals, about 1-10 (12th power) ohm/cm, so the eddy loss and skin effect are small, and it is suitable for high-frequency use. The saturation magnetization is low, so it is not suitable for high magnetic density occasions. The Curie temperature is relatively low.
2 Ferromagnetic materials: refers to materials with ferromagnetism. For example, iron-nickel-cobalt and its alloys, alloys of certain rare earth elements. Below the Curie temperature, the material has a larger magnetization intensity when external magnetization is applied.
3 Ferromagnetic materials: Refers to materials with ferrimagnetic properties, such as various ferrites, below the Neel temperature, the material has a greater magnetization strength when external magnetization is applied.
4 Permanent magnet material: The magnet is magnetized thick and the external magnetic field is removed, and it still has strong magnetism, which is characterized by high coercive force and large magnetic energy product. It can be divided into aluminum nickel cobalt, rare earth cobalt, neodymium iron boron and so on. Ferrite permanent magnets, for example, barium ferrite, strontium ferrite, other permanent magnets, such as plastic magnets.
5 Soft magnetic materials: materials that are easy to magnetize and demagnetize. Manganese-zinc ferrite soft magnetic material, its working frequency is between 1K-10M. Nickel-zinc ferrite soft magnetic material, the working frequency is generally 1-300MHZ.
6 Metal soft magnetic materials: Compared with ferrite, it has high saturation magnetic induction and low coercivity, such as engineering pure iron, iron-aluminum alloy, iron-cobalt alloy, iron-nickel alloy, etc., which are often used in transformers.
The terminology of magnets:
1 Saturation magnetic induction intensity: (saturation magnetic flux density) the magnetic induction intensity when a magnetic body is magnetized to a saturated state. In practical applications, saturation magnetic induction often refers to the magnetic induction under a certain specified magnetic field (basically the magnetic field when magnetic saturation is reached).
2 Residual magnetic induction intensity: From the saturation state of the magnetic body, the magnetic induction intensity (including the self-demagnetizing field) is monotonously reduced to 0.
3 Magnetic flux density coercive force, it is the magnetic induction intensity when the magnetic field intensity is changed monotonously along the saturation hysteresis loop from the saturation magnetization state of the magnetic body, so that the magnetic induction intensity B is reduced to 0.
4 Intrinsic coercive force: the magnetic field strength that reduces the magnetization M to 0 from the saturation magnetization state of the magnetic body.
5 Magnetic energy product: the product of the magnetic induction intensity and the magnetic field intensity at any point on the demagnetization curve of the permanent magnet.
6 Initial permeability: the limit value of the permeability of the magnetic body in the magnetic neutral state.
7 Loss tangent: It is the ratio of the imaginary part and the real part of the series complex permeability. Its physical meaning is the ratio of the loss energy to the stored energy of the magnetic material in each cycle of the alternating magnetic field.
8 Specific loss tangent: This is the ratio of the material's loss tangent to the initial permeability.
9 Temperature coefficient: Between two given temperatures, the measured change is divided by the temperature change.
10 The specific temperature coefficient of permeability: the ratio of the temperature coefficient of permeability to the permeability.
11 Curie temperature: At this temperature, the spontaneous magnetization is zero, that is, the critical temperature at which a ferromagnetic material (or submagnetic material) changes from a ferromagnetic state (or ferrimagnetic state) to a paramagnetic state.
