PURPOSE: To synthesize a ferromagnetic material contg. Fe8N excellent in the magnetic characteristics in high selectivity and high growth velocity by impressing electromagnetic wave energy in the decompression for two gaseous molecules contg. iron atom and nitrogen atom respectively and allowing the above- mentioned both molecules to react each other with the generated plasma.

CONSTITUTION: An iron atom-contg. gaseous molecule [e.g. Fe(CO)3, iron chloride or the like] and a nitrogen atom-contg. gaseous molecule (e.g. N2, NH3 or the like) are introduced into the inside of a vessel decompressed in 10-2W10-1Torr. Thereafter electromagnetic wave energy such as microwave, high frequency and radio wave is impressed for two gaseous molecules contained in the above-mentioned vessel to generate plasma. Thereby the above-mentioned both molecules are decomposed at the temp. lower than 300°C decomposition temp. of Fe3N and allowed to react each other. As a result, the production of Fe4N and Fe3N inferior in the magnetic characteristics is controlled and Fe8N is obtained in excellent selectivity.