Pure BaFe 12 O 19 nanoparticles, having single magnetic domain sizes, were obtained at 700°C using a process combining the citrate precursor method and spray technique. A neutralized aqueous solution, containing Ba 2+ and Fe 3+ chelated by citric acid, was nebulized to undergo thermal decomposition in a flowing air with a maximum temperature of 250°C. The dried solid precursor so obtained was calcined at different temperatures and was then chemically and physically characterized. Crystalline barium hexaferrites were formed at temperatures as low as 650°C, but calcination temperatures higher than 680°C were required to produce pure barium ferrite powder. Based on the obtained experimental results, the reaction mechanism for the aerosol-derived precursor to form BaFe 12 O 19 was proposed and discussed in this study.