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 mum. have been synthesised by wh at 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 coerci vity 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 13 0 degreesC, followed by calcination of the product phase at 850 degreesC fo r 45 min in air. The effects of the calcination temperature on the phase co mposition, particle size and shape as well as the magnetic properties of th e products have been investigated. It was found that the coercivity increas ed rapidly on increasing the calcining temperature from 650 to 750 degreesC and then exhibited a maximum at 850 degreesC. The saturation magnetisation increased on increasing the calcination temperature above 650 degreesC. (C ) 2001 Elsevier Science Ltd. All rights reserved.