Formation of cobalt ferrites from aqueous solutions of metal nitrates containing PVA: effects of the amount of PVA and annealing temperature

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Controlling magnetic properties of sol–gel synthesized cobalt ferrites (CoFe2O4) have been studied by variations in amount of polyvinyl alcohol (PVA) and annealing temperature. PVA of 24, 32, 40 and 48 g in 10% w/v aqueous solutions was used in the reaction between 10.592 g of Co(NO3)2·6H2O and 29.407 g of Fe(NO3)3·9H2O. The decrease in PVA led to the reductions in coercive field and squareness. However, X-ray diffraction peaks indicated that iron oxide (α-Fe2O3) and iron oxide hydroxide [FeO(OH)] were also formed when the PVA was less than 48 g. The optimized amount for obtaining single phase CoFe2O4 was therefore 48 g which was used for studies of heat treatment effect. Both coercive field and squareness were increased with the increase in annealing temperature from 280 to 680°C and then reduced with the further increasing temperature up to 900°C as a result of particles agglomeration.