When it comes to the relationship between temperature and magnetism, we must first understand a concept - "Curie temperature". Do you feel familiar when you hear the word, Curie? Did you think of the famous Mrs. Curie? This concept barely has a little relationship with Mrs. Curie.
More than 200 years ago, a famous physicist discovered a physical characteristic of the magnet in his laboratory, that is, when the magnet is heated to a certain temperature, its original magnetism will disappear. This great physicist is Ju Mrs. Rie's husband—Pierre Curie, later people called this temperature the Curie point, also known as the Curie temperature (Tc) or magnetic transition point.
Definition: The Curie temperature is the temperature at which a magnetic material changes between a ferromagnet and a paramagnet. When it is lower than the Curie temperature, the substance becomes a ferromagnet. At this time, the magnetic field related to the material is difficult to change. When the temperature is higher than the Curie temperature, the substance becomes a paramagnet, and the magnetic field of the magnet is easily changed with the change of the surrounding magnetic field.
Value: Curie temperature represents the theoretical working temperature limit of magnetic materials. The Curie temperature of NdFeB is 320-380 degrees Celsius. The Curie point is related to the crystal structure formed by magnet sintering.
What happens when the Curie temperature is exceeded? If the temperature reaches the Curie temperature, the molecules in the magnet move violently and demagnetize, which is irreversible.
After talking about the Curie temperature, let’s talk about the working temperature (Tw). In fact, the Curie temperature is only the temperature under laboratory conditions, or it can be said to be the ideal temperature, and the working temperature of the magnet is the material at the highest temperature at which the magnetism can be maintained in practice. The maximum working temperature of sintered NdFeB is much lower than its Curie temperature. Within the working temperature, the magnetic force will decrease as the temperature rises, but most of the magnetic force will recover after cooling.
The relationship between working temperature and Curie temperature: The higher the Curie temperature, the higher the working temperature of the magnetic material, and the better the temperature stability. Adding cobalt, terbium, dysprosium and other elements to sintered NdFeB raw materials can increase its Curie temperature.
The maximum service temperature of sintered NdFeB depends on its own magnetic properties and the selection of working point. For the same sintered NdFeB magnet, the closer the working magnetic circuit is, the higher the maximum operating temperature of the magnet and the more stable the performance of the magnet.
Therefore, the maximum operating temperature of the magnet is not a definite value, but changes with the degree of closure of the magnetic circuit. Under the premise of a given working point for sintered NdFeB magnets, the maximum working temperature and Curie temperature of each brand are as follows:
