Thermal conversion of an iron nitride-silicon nitride precursor into a ferromagnetic nanocomposite

Iron nitride films, FeN, in a pure form and in the form of a nanocomposite in silicon nitride were prepared by reactive sputtering using iron or iron disilicide, respectively, as targets in a nitrogen plasma. Iron nitride decomposes into the elements by heating in vacuum to 800 °C. Intermediate phases such as Fe₂N or Fe₄N form at lower temperatures. The nanocomposites contain the iron phases as particles with an average size of ∼5 nm dispersed in the amorphous silicon nitride matrix. The magnetic properties of the nanocomposites were established. The precursor FeN-Si₃N₄ film is paramagnetic, while the Fe-Si₃N₄, obtained by heating in vacuum, is ferromagnetic and shows typical superparamagnetic behavior. These films are of interest as recording media with superior chemical and mechanical stability and may be encoded by localized heating.