Why and How to Demagnetize

Demagnetization is necessary

The demagnetization of the sample refers to the case where the magnetic intensity H and the magnetic induction intensity B are zero together. Sometimes it is called the magnetic neutrality case, and the process of demagnetization of the sample is called the magnetic neutralization. Because the hysteresis loop is the process that the sample magnetism changes with the change of the external magnetic field, if the sample has magnetism at the beginning, the hysteresis loop does not start from zero, and there will be irregular hysteresis loop.

Two methods of demagnetization

1. Thermal demagnetization is to heat the sample above Curie point and then cool it slowly to room temperature without external field. Although the operation process of this method is complex and may lead to structural changes of the sample, it can achieve complete demagnetization.

Curie temperature, also known as Curie temperature or magnetic change point, refers to the temperature at which the material can be changed between ferromagnet and paramagnet, that is, the phase transition temperature at which the ferromagnet changes from ferromagnetic phase to paramagnetic phase.