Cobalt-doped ferrimagnetic iron oxides and process for producing them

摘要

A cobalt-doped, acicular ferrimagnetic iron oxide having an FeO content of about 16 to 24%, by weight, and a cobalt content of about 0.7 to 2.4%, by weight, the coercive force amounting to at least about 425 Oe+175 Oe/%, by weight, of Co is produced by precipitating and oxidizing a cobalt-containing aqueous iron (ii) salt solution, reducing the precipitate to Fe3O4, partially reoxidizing to adjust the FeO content and heat treating under inert conditions at a temperature from about 600 DEG to 800 DEG C.