What is the Hk of magnetic material?
Hk is only in the permanent magnetic material, it is the inflection point in the demagnetization process, the magnetic field size. The permanent magnetic material always keeps a strong magnetic state after magnetizing.
Only when the external magnetic field reaches the size of Hk, the permanent magnet begins to demagnetization rapidly and begins to lose magnetism. Therefore, Hk can generally reflect what kind of magnetic field environment, permanent magnet material can be used normally.
When there is a reverse external magnetic field acting on the permanent magnet, the magnetic field of the permanent magnet remains almost constant when the external magnetic field is not large enough.
