Synthesis of Fine Fe4N Powder and Its Magnetic Characteristics

Abstract

A pigment of Fe₄N particles for magnetic recording was prepared by nitrogenizing acicular metal iron powder. The chemical treatment needed to obtain stoichiometric Fe₄N powder was studied, and it was found that Fe₄N powder was obtained when the Fe powder was heated at about 400°C in a mixture of H₂–NH₃ (65–80 vol.%). The Curie point of the powder coincided well with that of bulk Fe₄N. The coercive force of Fe₄N 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.