Cobalt-doped ferrimagnetic iron oxides and process for producing them

摘要

Cobalt-doped acicular ferrimagnetic iron oxides with an FeO content of 16 to 24% by weight are described, in which the coercive force is at least 425 · Oe plus 175 Oe /% by weight of Co. The iron oxides are obtained by protecting acicular, cobalt-containing iron (III) oxide hydroxide obtained from aqueous iron (II) salt solutions by precipitation and oxidation at least partially in the presence of cobalt ions by modification with inorganic or organo-organic compounds against sintering, then reducing them to Fe3O4 and partially reoxidized to set an FeO content of 16-24% by weight of oxygen-containing gas, a temperature treatment being carried out at 600-800 ° C. under inert conditions after the FeO content has been set.