When a magnet encounters a high temperature that exceeds its ability to withstand, it will immediately lose some of its magnetism. How high a temperature is needed? This depends on the coercivity of the magnet, which is usually indicated by the letters after the magnet grade, such as N40H, with a maximum magnetic energy product of 40, and H represents a temperature resistance of 120°C. The higher the coercivity, the less likely it is to lose magnetism (demagnetization), and the more dysprosium metal is added to the magnet.
How much magnetism will it lose?
This depends on how well it is magnetically protected, and it helps if there is some iron around. Of course, this depends on the temperature, but it is a highly nonlinear effect. It does not lose any magnetism until it reaches a certain temperature, and then it quickly loses all magnetism. Note that the amount of magnetism it loses depends on how high the temperature is, not the length of time at a particular temperature. Once the magnet reaches a certain temperature, it will lose all the magnetism it can achieve at that temperature. How long will it take to lose magnetism?
For some tiny magnets, demagnetization will occur immediately. However, even for small magnets, it takes time for heat to transfer from the outer surface to the center. For example, a 1cm3 part takes several minutes. However, parts of the magnet close to the surface will lose performance immediately. 200°, whether in Fahrenheit or Celsius, is very high for magnets. Unless you have special, higher-grade magnets (UH or AH or better), you will completely ruin it.
Introduction to the coercivity of each grade of NdFeB magnets:
N-grade neodymium magnets: low coercivity
M-grade neodymium magnets: medium coercivity
H-grade neodymium magnets: high coercivity
SH-grade neodymium magnets: ultra-high coercivity
Uh-grade neodymium magnets: ultra-high coercivity
EH-grade neodymium magnets: extremely high coercivity
From N to EH, the later ones have higher temperature resistance and higher costs. Other high-temperature resistant magnets include samarium cobalt, ferrite, aluminum nickel cobalt, etc.
