圧粉磁心用スピネル型フェライト皮膜の電気抵抗に及ぼす熱処理の影響

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, the electrical resistivity of the powder magnetic core was decreased after annealing at 873 K, since FeO was formed in the spinel ferrite insulating layer. Based on the eutectoid transformation 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 2 steps heat treatment at 873 K and 773 K. The results showed that electrical resistivity was increased due to the disappearance of FeO by eutectoid transformation even in the insulating layer.