Cobalt-containing magnetic iron oxide and process for producing the same

Abstract

Cobalt-containing magnetic iron oxide particles extremely suitable for magnetic recording mediums, especially for image recording mediums and a process for producing the same from the precursor, .gamma.-FeOOH which is advantageous in industry are disclosed. Cobalt-containing magnetic iron oxide particles satisfying the following equations (1), (2) and (3): 20.ltoreq.SSA.ltoreq.50 (1) -16.70.ltoreq.log [V].ltoreq.-3.05 log [SSA]-11.35 (2) 0.10.ltoreq.Fe.sup.2+ /total Fe.ltoreq.0.30 (3) where SSA is a BET specific surface area (m.sup.2 /g), and V is a magnetic switching unit (cm.sup.3), can be produced by producing iron oxide particles having a concentration of Fe.sup.2+ of 0.10 to 0.36 as expressed by Fe.sup.2+ /total Fe from the precursor, .gamma.-FeOOH, and coating a cobalt compound or a combination of a cobalt compound and other metal compounds on the surfaces of the iron oxide particles.

Dependencies are inferred from the claim text.