Examination of precise measurement of DC magnetic properties of permalloy under low flux density more than a few mT

Permalloy is used in a magnetically shielded room to inhibit the penetration of external magnetic field, etc. The flux density in permalloy used in the shielded room is of the order of a few mT or lower. In order to examine the performance of such a shielded room, the dc magnetic properties at low flux density is necessary. In this paper, we developed a measurement method of dc (5 mHz) magnetic properties of permalloy under such a low flux density. It is shown that the dc magnetic properties could be measured more than 4 mT by paying the attention to the degaussing of specimen and applying the correction of drift and offset of measurement system.