Magnetic Properties of Fe-N Gradient Foils Irradiated with Nitrogen Plasma

Abstract

We investigated the saturation magnetization and structure of iron foils treated by nitrogen plasma irradiation. The surface of each nitrided foil was removed step by step by electropolishing, and the saturation magnetization of the nitrided foil was then measured. X-ray diffraction patterns were taken from the electropolished surface at each step. Various iron nitrides were formed at all depths of foils nitrided for 5 hours or more, and their quantity increased with the nitriding time. The outermost region of the surface layer irradiated with nitrogen plasma was composed of γ' -Fe 4 N and e-Fe 3 N, and the inner region was composed of α'-martensite. The saturation magnetization of α'-martensite in a foil nitrided for 13 hours was 223 emu/g. The nitrogen content of α'-martensite in the nitrided foil was 0.5 at%. The nitrogen content of a'-martensite in the foil nitrided at a surface temperature of 260°C with the cathode cooled to 15°C was 1.5 at% and 0. 5 at% in the nitrided foils when the cathode was not cooled.