MAGNETIC PARTICLES AND METHOD OF PRODUCTION THEREOF

摘要

Magnetic particles, particularly magnetic iron oxide particles, magnetic cobalt-containing iron oxide particles and magnetic metallic iron particles, which have a long axis diameter of 300 nm or less, an axial ratio of 5 or less, and a specific surface area of 40 m<2>/g (measured by BET method), and are useful as a recording element for a magnetic recording medium, and a method for the production thereof, which comprises reacting an aqueous solution containing trivalent iron ion with an equivalent or more amount of an aqueous alkali solution at a temperature of 30 DEG C or lower, aging the produced ferric hydroxide, subjecting the ferric hydroxide to hydrothermal reaction in an autoclave to produce alpha -ferric oxyhydroxide particles, filtering and drying the particles, and then reducing the particles with heating and optionally further oxidizing them, and also a magnetic recording medium prepared from the magnetic particles.