Preparation of Sr-based hexagonal ferrite by controlling the oxidation state of Fe

We have investigated synthesis conditions and magnetic properties of Sr2Fe2+2Fe3+12O22 (Sr2Fe2Y). The main Y-type phase was observed for the sample synthesized with the initial composition of Sr:Fe2+:Fe3+=1.5:2:8 sintered at TS=1200℃ and PO2 =10 Pa. The Curie temperature of Sr2Fe2Y was 643 K. The magnetization was 45.0 Am2/kg at T= 5 K and μ0H=7 T. The difference in magnetization from the ideal collinear spin arrangement of Sr2Fe2Y is due to the existence of a minor Fe3O4-like spinel phase. The yield of Sr2Fe2Y phase was estimated to be 83 wt.%, suggesting successful synthesis of the Sr2Fe2Y hexaferrite.