Magnetoplumbite and W-type barium ferrites as magnetic mixture with hematite

Abstract

Magnetic properties were studied on polycrystalline composite mixtures of magnetoplumbite-type BaFe₁₂O₁₉ and W-type BaCo₂Fe₁₆O₂₇ ferrites with α-Fe₂O₃. The respective ferrite mixtures were prepared with hematite in 0 to 70 mol% using solid state reaction. X-ray diffraction (XRD) analysis and magnetic measurement suggested the products were simple mixtures of the ferromagnetic BaFe₁₂O₁₉ or BaCo₂Fe₁₆O₂₇ with α-Fe₂O₃ even after sintering at 1250°C. Their magnetization decreased with the increasing contents of α-Fe₂O₃. Their electrical resistivities of higher than 10² Ωm were too large to observe their magnetic field dependence, magnetoresistance (MR) effect. Electrical resistivity decreased to 0.36 Ωm by the post annealing of the as prepared BaCo₂Fe₁₆O₂₇ with a small amount of α-Fe₂O₃ in Ar at 1000°C for 5 h. The improved electrical conductivity in 4 orders of magnitude showed the MR effect of 0.86% on the post annealed BaCo₂Fe₁₆O₂₇ product.