Preparation of Strontium Hexaferrite-Based Materials by Solution Combustion: Effects of Charges Arising in the Precursors and an External Magnetic Field

The generation of electric charges during the combustion of nitrate organic precursors in the synthesis of strontium hexaferrite SrFe₁₂O₁₉-based complex oxide materials, including those doped with lanthanum and cobalt ions, was established. The precursors included polyvinyl alcohol or glycine. The intensity of charge generation was lower for precursors containing a larger amount of the organic component. Magnetic characteristics of the samples (magnetization, coercive field) were measured. An external magnetic field applied during the hexaferrite synthesis significantly affected the coercive field of the samples, which could be increased via the formation of extended ensembles of nanoparticles. The effect was more pronounced for samples with a moderate level of charge generation. The relationship between the factors influencing the formation of extended aggregates was analyzed. The maximum coercive field was found for Sr_0.8La_0.2Fe_11.8Co_0.2O₁₉. One way to increase the coercive field is a two-stage magnetic heat treatment including a low-temperature stage. The formation of branched extended structures at the macro- and micro-levels was found during the combustion of glycine-containing precursors.