Acicular ferromagnetic iron oxide particles and process for producing the same

A process for producing acicular magnetic iron oxide particles having a saturation magnetization of 90 emu/g or more, comprising crystalline particles expressed by the formula FeOx (1.0<x<1.33) and modified with 2 to 15 atomic percent by weight zinc ions as expressed as Zn/Fe, which comprises the steps of:

• (a) heating and dehydrating acicular hydrous iron oxide particles containing a zinc component at a temperature of 300.degree. to 750.degree. C., reducing the dehydrated particles at a temperature of 300.degree. to 500.degree. C., and then heat-treating the reduced particles at a temperature of 400.degree. to 700.degree. C. in an inert atmosphere, or (b) reducing acicular iron oxide particles containing a zinc component at a temperature of 300.degree. to 500.degree. C., and then heat-treating the reduced particles at a temperature of 400.degree. to 700.degree. C. in an inert atmosphere, or (c) heat-treating acicular iron oxide particles expressed by the formula FeOx (1.0<x<1.33) containing a zinc component at a temperature of 400.degree. to 700.degree. C. in an inert atmosphere.