Effect of annealing temperature on the structural and magnetic properties of Ba-Pb-hexaferrite powders synthesized by sol-gel auto-combustion method

The annealing temperature (Ta) dependent development in phase purity, morphology and magnetic properties of BaxPb1-xFe12O19 (x = 0, 0.2, 0.4, 0.6, 0.8 and 1) powders synthesized via sol-gel auto-combustion route were studied. The hexagonal phase of PbFe12O19 forms directly via solid-state-reaction between α-Fe2O3 and PbO during annealing of the combustion product at Ta ~ 900 °C, but the BaFe12O19 phase forms at Ta ~ 1200 °C through the formation of BaFe2O4 and α-Fe2O3 as intermediate-phases at low Ta. The BaxPb1-x Fe12O19-phase purity of the samples depend on Ta. For Ta > 1000 °C, PbO evaporates from Pb-containing samples. With increasing Ta, growth of hexagonal-shaped sharp-edged particles was observed for Barium-rich samples, however, the sharp-edges dissolute for Lead-rich samples. High saturation magnetization was observed for Ba-rich samples annealed at 1100 °C. For all the studied samples, magnetic coercivity increases with x but decreases with Ta. The magnetic properties were correlated with the structure, microstructure and grain-size of the samples.