Influence of pH on characteristics of BaFe12O19 powder prepared by sol–gel auto-combustion

BaFe12O19 powders with nanocrystalline sizes were produced by sol–gel auto-combustion. Fe3+ and Ba2+, in a molar ratio of 11.5, were chelated by citric acid ions at different pH. After dehydration, auto-combustion and calcinations, BaFe12O19 powders were formed. TG/DSC indicated the action to form BaFe12O19 first occurred at about 800. XRD patterns of the annealed powders showed that the well-crystalline powder was produced when pH=10. In addition, the data from XRD showed the lattice parameters a and c, and the unit-cell volume V had a little decrease and the density went up with the increasing pH. The data from PPMS exhibited that pH in the starting solution had an important influence on magnetic properties. In this case, BaFe12O19 powder, of maximum magnetization M(3 T)≈60 A m2/kg, the remanent magnetization Mr≈33 A m2/kg and the intrinsic coercive Hc≈432 kA/m, was produced under the molar ratio of citric acid to the metal nitrate of 1.5 when pH=10.