Acicular magnetic iron oxide particles and process for producing the same

摘要

Acicular magnetic iron oxide particles comprising: acicular magnetite core particles having a ferrous content of from 10 to 24% by weight; a magnetite coating which is formed on said core particles by epitaxial growth and which has maghemite at least in a part of the surface of said magnetite coating; and a cobalt-containing oxide layer which is provided on said magnetite coating and which contains from 1.5 to 2.5% by weight of cobalt based on the total weight of said acicular magnetic iron oxide particles.