Controlling the composition and magnetic properties of strontium hexaferrite synthesized by co-precipitation method

Nanocrystalline strontium hexaferrite (SrFe12O19) powders have been synthesized using the co-precipitation–calcination route. The ferrite precursors were obtained from aqueous mixtures of strontium carbonate and ferric chloride by precipitating strontium and iron ions using 5 M sodium hydroxide solution. These precursors were calcined at different temperatures ranging from 800 to 1100 °C for constant calcination time 2 h in a static air atmosphere. Effects of Fe3+/Sr2+ mole ratio, annealing temperature and pH on the formation, crystalline size, morphology and magnetic properties were systematically studied. The powders formed were investigated using X-ray diffraction (XRD), scanning electron microscope (SEM) and VSM. The results obtained showed that the single-phase SrFe12O19 powders were achieved by decreasing the Fe3+/Sr2+ mole ratio from the stoichiometric value 12 to 9.23 and increasing the annealing temperature up to 900 °C for 2 h and pH 10. The maximum saturation magnetization (84.15 emu/g) was achieved by decreasing the Fe3+/Sr2+ mole ratio to 9.23 and the annealing temperature 1000 °C, annealing time 2 h and pH 10 due to the formation of a plate-like hexagonal-shape structure. Wide coercivities (2937–5607 Oe) can be obtained at different synthesis conditions. Moreover, the microstructure and the magnetic properties of the produced Sr–M ferrite powders were strongly dependent on he synthesis conditions.