M-type Barium Hexaferrite with Excessive Divalent Iron Synthesized by Spark Plasma Sintering Method

The precursor of M-type barium hexaferrite(BaM) with excessive divalent iron BaFe3+11.8Fe2+0.3O19 was prepared by chemical coprecipitation process in Ar atmosphere.The phase compositions,microstructures,and densities of sintered products synthesized by spark plasma sintering(SPS) method were investigated with XRD,SEM and Archimedes methods.The optimizing SPS condition for synthesizing single-phase and high-compactness BaM materials with excessive divalent iron is holding for 30min at 850℃ and 10MPa.The crystalline reaction process is composed of the decomposition of the precursor into α-Fe2O3 and Fe3O4 or γ-Fe2O3 at low temperature and the crystallization of BaM with excessive Fe2+ at high-temperature,without intermediate phase BaFe2O4 forming in the whole process.Saturation magnetization and coercivity of single-phase BaM materials with excessive divalent iron are of 58.2A·m2·kg-1 and 255kA·m-1,respectively,which imply that the excessive divalent irons spin upward at 2a site in FeO6 octahedron.