| 摘要 |
PURPOSE:To obtain the titled powder which is excellent in dispersion properties, the distribution of coersive force and electromagnetic conversion characteristics and available for high-density recording, etc., by respectively forming an adsorption layer of ferrous compd., an inner layer of ferrous and cobalt compds. and an outer layer of cobalt compd. on the surface of specified nuclear crystal. CONSTITUTION:An alkaline solution suspended with magnetic iron oxide powder is prepared. At first, ferrous salt is added to this solution. Ferrous cpd. is absorbed on the surface of the suspended iron oxide powder and forms ferrous cpd. layer. After described time, which about half amount of the ferrous salt in the solution is consumed by adsorption, cobalt salt is added to the solution. Remained ferrous salt and cobalt salt in the solution are co-absorbed on the surface of the ferrous cpd. layer. In the proceeding of the co-absorption, formed layer is gradually become cobalt cpd. rich accompanied with consumption of firstly added ferrous salt in the solution by the adsorption. And finally, only cobalt cpd. is absorbed on the surface of the co-absorbed layer. Temperature of the solution have to always keep <30 deg.C. Then the obtained particles are subjected to drying. Cobalt-contg. ferromagnertic iron oxide powder has >=35m<2>/g specific surface area by BET method, >=700 Oe coercive force and <=0.08 ratio of bivalent iron to all amounts of iron.
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