Structural and Magnetic Characterization of Single-phase Sponge-like Bulk α-Fe16N2

Improvements of the two-step reaction sequence starting from gamma-Fe2O3 enabled us to synthesize alpha-Fe16N2 in single phase according to the applied diffraction methods. Simultaneous Rietveld refinements were carried out on powder X-ray and neutron diffraction data. Scanning electron microscopy images of the in situ formed alpha-Fe and alpha-Fe16N2 indicate the formation of pores during reduction and ammonolysis reaction, respectively, resulting in a sponge-like morphology of the alpha-Fe16N2 particles and simultaneously a large surface area facilitating a complete reaction at comparably low temperatures of 125 degrees C. The large surface area is susceptible to the sorption of impurities and indeed chemical analysis reveals significant oxygen and hydrogen contamination of the sample. From EDX measurements in combination with the results of chemical analysis a sorption of humidity to the surface seems to be more likely to explain this contamination than an incorporation of oxygen into the bulk of the sample. Magnetization measurements on the bulk sample of alpha-Fe16N2 did not reveal any indication for the presence of a proposed giant magnetic effect.