Synthesis of ultra-fine particles of strontium hexaferrite by a modified co-precipitation method

Uniform size and ultra-fine particles of strontium hexaferrite, SrFe12O19, with a particle size range from 0.1 to 0.2 μm have been synthesised by what is termed modified co-precipitation from mixed aqueous solutions of iron and strontium nitrates. The results obtained here show that single domain particles of strontium hexaferrite exhibiting a significantly higher coercivity of 444.5 kA/m (5.55 kOe) can be produced by hydrothermally processing a NaOH-precipitated precursor nitrate solution at a lower temperature of 130°C, followed by calcination of the product phase at 850°C for 45 min in air. The effects of the calcination temperature on the phase composition, particle size and shape as well as the magnetic properties of the products have been investigated. It was found that the coercivity increased rapidly on increasing the calcining temperature from 650 to 750°C and then exhibited a maximum at 850°C. The saturation magnetisation increased on increasing the calcination temperature above 650°C.