Morphological and magnetic properties of sol-gel synthetized meso and macroporous spheres of barium hexaferrite (BaFe₁₂O₁₉)

Highlights: • 1.5 µm porous spheres of BaFe₁₂O₁₉ were synthetized by the sol-gel method. • Surfactant Tween20 (C₅₈H₁₁₄O₂₆) enabled the creation of the mesoporous structure. • Polystyrene spheres (PS) were used as the template for the formation of macropores. • Spheres resembled a nest or ball-of-yarn type of elongated BaFe₁₂O₁₉ crystals. • Magnetic properties are evaluated as function of the calcination temperature. - Abstract: Porous spherical aggregates of barium hexaferrite (BaFe₁₂O₁₉) with 1.5 µm in diameter were synthetized by the surfactant-assisted sol-gel method. The surfactant Tween20 (C₅₈H₁₁₄O₂₆), which enables mesoporous structures, as well as polystyrene spheres (PS), as the template agent for the formation of macropores, were used. Two synthetic routes (hereafter named A and B), whose difference was the absence or presence of PS, were followed for synthesis. X-ray diffraction (XRD), scanning electron microscopy (SEM) and transmission electron microscopy (TEM) in high resolution mode (HRTEM) were used for characterization. Size and morphology of the spheres were similar in both cases and they resemble a nest or ball-of-yarn type structure. Pore size and BaFe₁₂O₁₉ crystal size produced by the two routes are different. The magnetic properties of the spheres were evaluated using a vibrating sample magnetometer (VSM) as function of the calcination temperature. The spheres present ferromagnetic behavior in both routes.