Synthesis of Fine Fe₄N Powder and Its Magnetic Characteristics

Abstract

A pigment of Fe 4 N particles for magnetic recording was prepared by nitrogenizing acicular metal iron powder. The chemical treatment needed to obtain stoichiometric Fe 4 N powder was studied, and it was found that Fe 4 N powder was obtained when the Fe powder was heated at about 400°C in a mixture of H 2 –NH 3 (65–80 vol.%). The Curie point of the powder coincided well with that of bulk Fe 4 N. The coercive force of Fe 4 N was 640 Oe, which is considerably smaller than that of the Fe powder used as the starting material. The dispersion of magnetic anisotropy was measured by a torque meter, and the decrease in the coercivity of nitrogenized iron powder was attributed to the exchange anisotropy of the surface layer.