25. What's curie temperature
With rising of temperature, the thermal shock of basic particles will speed up, the arrangement of the microscopic magnetism inside the magnetic materials will disorder gradually. Macroscopically, the magnetic polarization intensity J will decrease with the rising of temperature. When the temperature rises to a certain degree, the magnetic polarization intensity turns to 0. At this time, the magnetism of the magnets will be equal with the nonmagnetic objects like air. The temperature at this moment is the Curie temperature (known as Tc). Curie temperature Tc is only relative to the ingredients of alloys, has no connection with the microstructure appearance and other distributions.
The Curie temperature Tc represents the theoretic highest working temperature. In fact, the actual working temperature Tw is far lower than Tc.
The Curie temperature of NdFeB is 312 °C. Tc is an important parameter of magnetic materials, the higher Tc is, the higher working temperature and temperature stability of the magnetic material will be. The Curie temperature of magnetic materials could be improved if Cobalt and Dysprosium are added, Therefore products in high coercive force like H, SH, UH, EH, AH series are usually added Dy to improve Tc.
What's more important, the working temperature of any permanent magnets was not only relevant to the Tc of the magnets, but also to the magnetic performance index, Hcj and the working status in magnetic circuit.
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