In the application field of NdFeB magnets, there is a close relationship between the magnetism and temperature. When the temperature of the magnet exceeds a certain threshold, permanent demagnetization will occur, and the maximum operating temperature that different grades of NdFeB magnets can withstand varies.
Curie temperature
When studying the effect of temperature on magnetism, "Curie temperature" is a key concept. The naming of this term is closely related to the Curie family. In the early 19th century, the famous physicist Pierre Curie discovered in his experimental research that when a magnet is heated to a certain temperature, its original magnetism will completely disappear. Later, people named this temperature Curie point, also known as Curie temperature or magnetic transition point.
From a professional definition, Curie temperature is the critical temperature at which magnetic materials achieve the state transition between ferromagnetic and paramagnetic materials. When the ambient temperature is lower than the Curie temperature, the material exhibits ferromagnetic properties; when the temperature is higher than the Curie temperature, the material turns into a paramagnet. The height of the Curie point mainly depends on the chemical composition and crystal structure characteristics of the material.
When the ambient temperature exceeds the Curie temperature, the thermal motion of some molecules in the magnet intensifies, the magnetic domain structure is destroyed, and a series of ferromagnetic properties such as high magnetic permeability, hysteresis loop, magnetostriction, etc. associated with it will disappear, and the magnet will undergo irreversible demagnetization. Although the demagnetized magnet can be re-magnetized, the required magnetization voltage is much higher than the first magnetization voltage, and after re-magnetization, the magnetic field strength generated by the magnet is usually difficult to restore to the initial level.
Material | Curie temperature Tc (℃) | Maximum operating temperature Tw (℃) |
NdFeB | 312 | 230 |
Working Temperature
Refers to the temperature range that the neodymium magnet can withstand during actual use. Due to the differences in thermal stability of different materials, the corresponding operating temperature range is also different. It is worth noting that the maximum operating temperature of neodymium is significantly lower than its Curie temperature. Within the operating temperature range, as the temperature increases, the magnetic force of the magnet will decrease, but after cooling, most of the magnetic properties can be restored.
There is an obvious positive correlation between Curie temperature and operating temperature: Generally speaking, the higher the Curie temperature of a magnetic material, the higher its corresponding upper limit of operating temperature, and the better its temperature stability. Taking sintered NdFeB material as an example, by adding elements such as cobalt, terbium, and dysprosium to the raw materials, its Curie temperature can be effectively increased, which is why high coercivity products (such as H, SH, etc. series) generally contain dysprosium.
Even for the same type of magnet, different grades of products have different temperature resistance due to differences in composition and microstructure. Taking NdFeB magnets as an example, the maximum operating temperature range of different grades of products is roughly between 80℃ and 230℃.
Coercivity Level | Max Working Temperature | |
N | Normal | 80 ℃ |
M | Medium | 100 ℃ |
H | High | 120 ℃ |
SH | Super High | 150 ℃ |
UH | Ultra High | 180 ℃ |
EH | Extremely High | 200 ℃ |
AH | Aggressively High | 230 ℃ |
Factors affecting the actual working temperature of NdFeB magnet
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