Demagnetization field

The demagnetizing field has a complex effect on the micro-inhomogeneity of the external magnetic field of the permanent Strong Neodymium Magnets suppliers.

In engineering, permanent magnets are used in an open circuit, and there is a demagnetizing field, which is one of the significant differences between permanent magnets and electromagnets. When the permanent magnet is magnetized under its action, the internal magnetic field is not equal to the external magnetic field. The size and distribution of the demagnetizing field are mainly determined by the geometry and size of the permanent magnet. When a demagnetizing field exists, even if it is magnetized in a uniform external magnetic field, since the magnetic field generated inside the permanent magnet is not uniform, the permanent magnet cannot be guaranteed in most cases. Absolutely uniform magnetization of the magnet. The theory proves that only ellipsoidal permanent magnets can meet the requirements of uniform magnetization.

Due to the uneven magnetization caused by the demagnetization field, according to the ampere molecular current point of view, the internal molecular current of the permanent magnet cannot be completely offset, and the permanent magnet has only the surface macromolecular current. Under non-ideal conditions, the internal molecular current of the permanent magnet cannot be completely offset. The remaining part of the micro current, they also generate a magnetic field, which is equivalent to countless “small permanent magnets”. Macroscopically, the magnetic field generated by the “small permanent magnet” and the overall external magnetic field of the permanent magnet under non-ideal conditions are vectorially superimposed, which affects the remanence Distribution such as magnetization deflection angle produces complex systemic microscopic effects.

Process factors

From the analysis of the principles of magnetism and magnetic materials science, the inhomogeneity of the external magnetic field of a permanent magnet is essentially caused by the inhomogeneity of its magnetic structure. For anisotropic permanent magnets, the quality of the powder particles is to ensure that the permanent magnet has a good microscopic magnetic structure And the primary condition of orientation. The ideal magnetic powder particles are:

The powder particle size is small and the distribution is narrow, all powder particles are single crystals.

The powder particles are elliptical.

Few crystal defects of powder particles.

Less impurities and gas adsorbed on the surface of powder particles.

For NdFeB permanent magnets, using the fast scale (SC) + hydrogen crushing (HD) + jet mill (JM) process, the technical results of the manufactured powder particles are somewhat close to the ideal state, but the process also needs to be optimized. Improvements can produce powder particles close to the ideal model. For samarium-cobalt permanent magnets, due to the difference in alloy properties, it is impossible to simply apply the advanced powdering process of neodymium iron boron permanent magnets such as jet milling in actual production. The elliptical shape close to the ideal model can be manufactured through processes such as oxidation-reduction diffusion. Powder particles. If the traditional powder metallurgy process is adopted, the main problem is that the powder particle size distribution range is relatively wide, the shape is diverse, and the crystal defects are many.

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