superparamagnetische fine particles of iron oxide and magnetic intermediate forms which they contain.

摘要

Superparamagnetic fine particles of iron oxide, suitable for use in a magnetic recording medium, have an unsaturated fatty acid adsorbed on the surface thereof, a magnetization of not less than 50 Am2/kg (50 emu/g), a rate of change of magnetization of not more than 10%, and an Fe2+ content (calculated as a Fe2+:Fe3+ molar ratio) of from 0.16 to 0.5:1.