Why can not heat treatment of magnetic material exceed Curie temperature?
Below the temperature of the Curie point, the substance becomes ferromagnetic, where the magnetic field associated with the material is difficult to change. When the temperature is higher than the temperature of the Curie point, the material becomes a paramagnetic material, and the magnetic field of the magnet can easily change with the change of the surrounding magnetic field. Therefore, heat treatment of magnetic material must not exceed the Curie temperature. Once it exceeds, the magnetism disappears.
The ferromagnetic material is magnetized with strong magnetism, but with the increase of temperature, the thermal motion of metal lattice intensifies will affect the ordered domain moment, when the temperature reaches the neat enough to break the domain magnetic moment, magnetic domain disintegrated, the average magnetic moment becomes zero, the ferromagnetic material magnetic disappear into CIS magnetic material, a series of ferromagnetic properties associated with magnetic domains (such as high permeability, hysteresis loop, magnetostrictive etc.) disappeared. The permeability of the ferromagnetic material of the corresponding permeability into paramagnetic substance.
The temperature of Curie is essentially a magnetic transition temperature point, which means the temperature at which the material can change between the ferromagnet and the magnet, i.e., the phase transition temperature of the ferromagnetic phase from the ferromagnetic phase to the paramagnetic phase.
