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.