The effect of porosity on coercive force in iron powder cores with different porosities was analyzed quantitatively. The coercive force of the iron powder cores decreased 11.0Am-1 with a decrease in porosity of 0.01. From in-situ observation by Kerr effect microscopy, nucleation of the reverse domain was observed in local areas along narrow gaps such as the contact interface between particles and fine pores among particles, and nucleation of the reverse domain did not occur at coarse pores. This indicates that the local decrease in the diamagnetic field with a decrease in porosity may be reduced in these areas, resulting in a decrease in coercive force. This result suggests that densification of iron powder cores can be an effective method for reducing coercive force.
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