nalformiga magnetic particles of gamma feŸ2oŸ3 seen to framstella them and magnetic tape comprising the particles

摘要

A process is disclosed for obtaining acicular magnetic particles of gamma -Fe2O3 modified with Fe++ and Co++ ions. The product thus obtained and magnetic tapes containing said product are also disclosed. A suspension of acicular gamma -Fe2O3 in an aqueous solution of soluble Fe++ and Co++ salts is prepared. NH3 is then added in such quantity that the molar ratio NH3/(Fe+++Co++) is between 2.1 and 3, and the whole mass is then heated up to 100 DEG -200 DEG C. When the molar ratio Fe++/Co++ is greater than about 2.5, it is necessary to operate in the presence of a metered quantity of oxygen or of an oxygen-containing gas; when the ratio is smaller or equal to about 2.5, the presence of a metered quantity of oxygen is optional.