1. Magnet materials
The magnetic properties of different materials vary. For example, Nd-Fe-B permanent magnets are one of the permanent magnet materials with the strongest magnetism nowadays. The microscopic structure and domain characteristics inside it enable it to generate a higher surface magnetic flux density under the same conditions such as size compared with materials like ferrite magnets. This is because Nd-Fe-B materials have a high remanence (Br). Remanence refers to the magnetic induction intensity remaining on the surface of the material when the magnetic field strength is reduced to zero after the magnetic material is magnetized to saturation, and the surface magnetic flux density is closely related to remanence.
SmCo magnets have good high-temperature resistance and corrosion resistance properties, and the magnetic characteristics of the material itself also determine that it can maintain a relatively stable surface magnetic flux density under certain working environments.
2. Shape and size of the magnet
• Shape
For magnets with regular shapes, such as cylindrical magnets, the magnetic field distribution is relatively symmetrical. The magnitude of the surface magnetic flux density will be affected by the shape and position of the magnetic poles. In the case of horseshoe-shaped magnets, the special shape of the magnetic poles makes the magnetic field distribution relatively concentrated between the two poles, and the surface magnetic flux density near the magnetic poles will be relatively high.
For magnets with irregular shapes, the magnetic field distribution is complex, and the surface magnetic flux density varies greatly at different positions. For example, if a magnet is processed into a complex special-shaped structure, the surface magnetic flux density at the protruding corners may be enhanced because the magnetic field is more likely to spread outward at these parts.
• Size
Generally speaking, for magnets with similar shapes and made of the same material, the larger the size, the higher the surface magnetic flux density may be. This is because magnets with larger sizes have a relatively larger number of magnetic domains inside and can generate a stronger magnetic field. For example, among two cylindrical magnets made of the same material, a longer and thicker magnet may have a higher surface magnetic flux density than a shorter and thinner one, provided that they are magnetized to the same extent.
3. Degree of magnetization
The magnetization process of a magnet has an important impact on the magnitude of the surface magnetic flux density. If a magnet is not fully magnetized during the manufacturing process, the surface magnetic flux density will be low. The higher the magnetization intensity, the higher the surface magnetic flux density usually is. For example, during the production process, by increasing the external magnetic field strength or extending the magnetization time, the magnetic domains inside the magnet can be better aligned, thereby increasing the surface magnetic flux density. However, each magnet material has its saturation magnetization intensity, and after reaching this limit, even if the magnetization conditions are further increased, the surface magnetic flux density will not continue to increase.
4. Working environment temperature
Temperature changes will affect the surface magnetic flux density of a magnet. For most magnet materials, as the temperature rises, their magnetism will gradually weaken and the surface magnetic flux density will also decrease. This is because the increase in temperature will lead to the intensification of the thermal motion of the magnetic domains inside the magnet and disrupt the orderly arrangement of the magnetic domains. For example, the magnetism of Nd-Fe-B magnets will decrease significantly in a high-temperature environment, and the surface magnetic flux density will also decrease accordingly. However, SmCo magnets have a relatively high working temperature range and can resist the impact of temperature on the surface magnetic flux density to a certain extent.
5. Internal structural defects of the magnet
Internal structural defects of a magnet will affect the surface magnetic flux density. If air holes, cracks or impurities appear during the production process of a magnet, they will interfere with the normal arrangement of magnetic domains and thus reduce the surface magnetic flux density. For example, during the sintering process of Nd-Fe-B magnets, if the sintering is incomplete and there are tiny air holes inside, the magnetic field will be disordered at these parts, resulting in a decrease in the surface magnetic flux density.
