A citric acid precursor method was used to prepare MnFe/sub 2/O/sub 4/ and (Mn,Zn)Fe/sub 2/O/sub 4/ powder. Citric acid was added into an aqueous solution, which contained nitrates of iron, manganese, or zinc in stoichiometric ratios to form the required ferrites, to chelate the metallic ions. The pH values of stating aqueous solutions were adjusted using NH/sub 4/OH. After adding glycol into the solution and raising the solution temperature to 353 K, esterification caused the formation of the required solid precursors. The dried solid precursors so obtained were then pyrolyzed to form the corresponding oxides. The characteristics of solid powder were studied using XRD and SEM. Crystalline MnFe/sub 2/O/sub 4/ powder was obtained at 623 K for all pH of the starting solutions used. In air , Mn/sup 2+/ in MnFe/sub 2/O/sub 4/ powder was oxidized to form Mn/sub 3+/ at temperatures about 873 K, resulting in phase segregation. Zn/sup 2+/ or Mg/sup 2+/ was added into the compositions and succeeded, in some extent, preventing the oxidation of Mn/sup 2+/. Crystalline (Mn,Zn)Fe/sub 2/O/sub 4/ powder was obtained at 1,273 K for all pH range of starting solutions used.
