Abstract
► The citrate sol–gel combustion route is used to synthesize BaFe12O19 particles. ► Sintering at temperatures up to 1100°C resulted in obtaining single domain particles. ► Unusually low initial Fe/Ba molar ratio of 4 gives the best magnetic properties. ► BaFe2O4 phase in the samples having Fe/Ba ratio ≤10.5 was removed by HCl etching.
BaFe12O19 particles have been synthesized by citrate sol–gel combustion route in a wide temperature range between 800 and 1200°C with initial Fe/Ba molar ratios between 12 and 2. Structural, morphological and magnetic properties of the powders have been investigated by XRD, FT-IR, SEM and magnetization measurements. It was observed that both coercivity and specific saturation magnetization increase with annealing at temperatures up to 1100°C, where a transition from single to multi domain structure occurs. To prevent formation of the hematite phase (α-Fe2O3), samples with different Fe/Ba molar ratios between 12 and 2 have been prepared and an intermediate phase, BaFe2O4, which may occur in Ba-rich samples has been removed by etching the powders in diluted hydrochloric acid. In this way, it was shown that single domain barium hexaferrite particles having high saturation magnetization, close to the theoretical value, and high coercivity can be synthesized with the initial Fe/Ba molar ratio of 4 in the sol–gel method. The chemical composition of this sample was determined as BaFe11.80O19.45 by the EDS analysis and Ba1.05Fe11.54O18.4 using an ICP-MS device. Both are very close to the theoretical formula.