Precursor-directed synthesis of quasi-spherical barium ferrite particles with good dispersion and magnetic properties

Abstract

The precursor-directed method has been firstly used for the preparation of M-type barium ferrite (BaFe₁₂O₁₉) particles in this article, where Fe₃O₄ microspheres were selected as the precursor. During the preparation process, it can be found that the volume ratio of water to ethanol plays an important role in determining the crystalline phase, and a high-purity magnetoplumbite structure can be achieved under the optimized conditions. Thanks to the morphology and dispersion of Fe₃O₄ microspheres, the obtained product presents a quasi-spherical shape, good dispersion, and relatively uniform particle size even after high-temperature heat treatment. Especially, the as-prepared barium ferrite exhibits excellent magnetic properties with both high intrinsic coercivity (5342 Oe) and large saturation magnetization (68.3 emu g⁻¹), which are better than most results from some unconventional techniques. A series of Co–Ti substituted barium ferrite particles [Ba(CoTi)_xFe_12−2xO₁₉, 0.25 ≤ x ≤ 1.0] are also prepared through the same technique by using Co–Ti substituted Fe₃O₄ microspheres as precursors, and they also display high-purity crystalline phase, quasi-spherical shape, and good dispersion, indicating that this route can be versatile for barium ferrite with different chemical compositions. However, with an increasing heteroatom content, the intrinsic coercivity and saturation magnetization drastically decrease because of the selective substitution of Fe³⁺ sites by Co²⁺ and Ti⁴⁺ in the magnetoplumbite structure.