PURPOSE: To obtain Co-containing iron oxide magnetic powder having excellent mangentic characteristics, age stability and thermal stability, by covering the surface of an acicular iron oxide magnetic particle with a layer of a bivalent iron oxide and with a Co-containing iron oxide layer, and heating the laminated powder under specific condition.
CONSTITUTION: An iron oxide layer is applied to the surface of an acicular iron oxide magnetic particles such as γ-Fe2O3 by using ferrous sulfate etc. containing bivalent iron ion. The coated surface is further coated with a Co-containing iron oxide layer using cobalt sulfate and ferrous sulfate. The laminated iron oxide particle is heat-treated at 200W400°C in an inert gas atmosphere or in vacuum. A high-quality iron oxide layer uniformly containing bivalent iron ion and cobalt is formed by the treatment. The cobalt ion is oriented along the surface magnetic field of the acicular iron oxide magnetic particle, and magnetic particles having large uniaxial anisotropy along the direction of long axis and having improved coercivity can be obtained by this process.
KITAOKA SUSUMU
KITAHATA SHINICHI
