2019 Volume 60 Issue 6 Pages 1061-1065
The powder magnetic core having a spinel ferrite insulating layer has enabled high magnetic flux density and high electrical resistivity, because spinel ferrite exhibits magnetic insulating properties. However, its the electrical resistivity of the powder magnetic core was reduced after annealing at 873 K, since FeO was formed in the spinel ferrite insulating layer. The eutectoid transformation caused the decomposition of FeO, which decompose into Fe3O4 and α-Fe at the temperature range below 833 K. We verified the possibility of eutectoid transformation of FeO in the insulating layer by the two-step heat treatment at 873 K and 773 K. The presented results clearly showed that the two-step heat treatment increases the electrical resistivity of the insulating layer due to the disappearance of FeO by eutectoid transformation even in the insulating layer.
This Paper was Originally Published in Japanese in J. Jpn. Soc. Powder Powder Metallurgy 65 (2018) 171–175.
