Physicochemical properties of powders of variable composition based on alpha -Fe//2O//3, BaFe//1//2O//1//9 and CoFe//2O//4 were investigated. Regions of formation of Co- and Ba-containing ferrite phases upon thermal treatment of their coprecipitated difficulty soluble compounds (hydroxides, carbonates) were established. Their magnetic properties were studied, and the possibility was shown of using them as fillers for elastic magnets and other magnetically rigid materials.