Spinel-type ferrimagnetic particles process for producing the same, and magnetic recording medium using the same

Abstract

Spinel-type ferrimagnetic particles having a composition represented by the formula: (MO).n/2(Fe2O3) wherein M is a divalent metal; and n is a molar ratio of Fe to M (n=Fe/M) which is from more than 2.05 to less than 2.5 (2.05<n<2.5), containing a superparamagnetic component in an amount of not more than 2% by mass, and having an average particle diameter of 5 to 30 nm, said spinel-type ferrimagnetic particles being respectively coated on surface thereof with a hydroxide of at least one metal selected from the group consisting of Si, Al, P and Zn in an amount of not more than 10% by mass, calculated as the metal, as well as a magnetic recording medium containing the spinel-type ferrimagnetic particles. The spinel-type ferrimagnetic particles can exhibit a high coercive force irrespective of fine particles, and are excellent in dispersibility and chemical stability, as well as the magnetic recording medium for high-density recording can exhibit not only excellent frequency characteristics and high output characteristics, but also an excellent weather resistance and a high reliability.

Dependencies are inferred from the claim text.