Synthesis and characterization of Fe16N2 in bulk form

Abstract

Using molecular beam epitaxy and ion implantation, Japanese workers have formed Fe16N2 in thin Fe films. They report a large magnetic induction for this nitride, ≥2.8 T. In the present study, Fe16N2 has been prepared in bulk form by treating Fe powder with NH3/H2 gas mixtures at temperatures in the range 660–670 °C. The γ phase alloy, which forms under these conditions, was quenched to room temperature to form the α′-Fe-N phase and then heat treated at 120–150 °C to form the α″-Fe-N phase. The α′ phase has been prepared in 80% purity, the other phase being nonmagnetic γ-Fe-N. The α″ phase has been prepared in 50% purity, the impurity phases being α-Fe and γ-Fe-N. Magnetic measurements give saturation magnetizations at room temperature of 250±10 emu/g (2.6μB/Fe) for the α′ phase, 285±10 emu/g (2.9μB/Fe) for the α″ phase, and essentially zero for the γ phase. Mössbauer measurements confirm that nitrogen austenite is nonmagnetic. The anisotropy of Fe16N2 is small but detectable.