Abstract: It is not easy to determine the value of the needed reverse external magnetic field in the experiment of static magnetization curve and magnetic hysteresis curve measurement, when the remanent magnetism is very little （ no more than 2.5mT）, so it is hard to realize complete demagnetization. After analysis of the related theory, this paper makes a quantitative study on the relation of demagnetization process and reversible magnetic area. The results have shown that the effective, reverse, minimum external magnetic intensity is approximately equal to the critical external magnetic intensity of reversible and irreversible magnetic area, and the value is nearly 0.55 times of coercive force of the material.

Key words: demagnetization, reversible magnetic area, effective reverse external magnetization, coercive force