Mössbauer and Magnetic Investigation of Iron Nitride with Martensite Structure Synthesised from Oxy-hydroxide Type Precursor

Fe16N2 fine particles were prepared by reduction in 5% H2/Ar gas mixture flow, starting from goethite or hematite precursors, followed by nitridation in ammonia gas flow. Small amounts of metallic iron and iron oxide are present besides the main phase which is an ordered iron nitride having martensite structure (α ’’ -Fe16N2) as revealed by Mössbauer spectroscopy measurements. However, X-ray diffraction data do not show any traces of oxides due to their high degree of amorphization. When nitridation is performed at about 150 0 C, Fe4N phase begins to form and its presence deteriorates the magnetic properties. The samples prepared by nitridation of goethite present better magnetic properties compared to those obtained by nitridation of hematite. Magnetic and Mössbauer measurements performed at ambient temperature were corroborated in order to extract the magnetization at saturation value for each phase which occurs in the obtained samples. The corresponding values are 226 emu/g for Fe16N2 and 198 emu/g for metallic iron contained in the prepared powders.