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. © 2007 Elsevier B.V. All rights reserved.