What is the mechanism of performance degradation of NdFeB Magnets in high temperature environments?

NdFeB magnet is the third generation of rare earth permanent magnet material developed in the 1980s. Its theoretical magnetic energy product reaches 64 MGOe, and the actual magnetic energy product of the magnet is also as high as 59 MGOe. However, the performance of this kind of magnet will degrade in high-temperature environments. The mechanism is mainly related to the Curie temperature, microstructure, exchange coupling between grains and coercive force mechanism of the magnet.
First, NdFeB magnets have a Curie temperature of 320°C, which is much lower than some other types of magnets, such as SmCo magnets. The Curie temperature is the critical temperature at which a magnetic material loses its ferromagnetism, so when the operating temperature of a magnet approaches or exceeds its Curie temperature, the magnetic performance will decrease significantly.
Secondly, the microstructure and composition of the magnet also have an important impact on its performance. Grain boundary diffusion (GBDP) is a method of heat treatment of magnets. By changing the microstructure and composition of the magnet, magnetic isolation between grains is achieved, thereby improving the exchange coupling between grains. However, even if the magnet structure is optimized through methods such as grain boundary diffusion, the coercive force of NdFeB magnets is still far smaller than its theoretical value, and there is a certain gap between it and the needs of practical applications.
Furthermore, coercive force is one of the important indicators to measure the magnetic properties of magnets. The intrinsic coercive field of NdFeB magnets is only about 20% of its magnetocrystalline anisotropy field, which means that the magnet is easily affected by external magnetic fields at high temperatures, resulting in the degradation of its magnetic properties.
To sum up, the mechanism of performance degradation of NdFeB magnets in high-temperature environments mainly includes its lower Curie temperature, the influence of microstructure and composition, and the limitations of the coercive force mechanism. These factors work together to cause the magnet to lose part or all of its magnetism at high temperatures, thus limiting its application in high-temperature environments.
In order to further improve the performance stability of NdFeB magnets at high temperatures, researchers are working on optimizing magnet materials, improving preparation processes, and exploring new heat treatment methods to increase their Curie temperature, enhance coercive force, and improve microscopic structure etc. These efforts are expected to open up broader prospects for the application of NdFeB magnets in high-temperature fields.