SYNTHESIS AND CHARACTERIZATION OF FE16N2 IN BULK FORM

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, greater-than-or-equal-to 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-degrees-C. The gamma phase alloy, which forms under these conditions, was quenched to room temperature to form the alpha'-Fe-N phase and then heat treated at 120-150-degrees-C to form the alpha''-Fe-N phase. The alpha' phase has been prepared in 80% purity, the other phase being nonmagnetic gamma-Fe-N. The alpha'' phase has been prepared in 50% purity, the impurity phases being alpha-Fe and gamma-Fe-N. Magnetic measurements give saturation magnetizations at room temperature of 250+/-10 emu/g (2.6 muA(B)/Fe) for the alpha' phase, 285+/-10 emu/g (2.9mu(B)/Fe) for the alpha'' phase, and essentially zero for the gamma phase. Mossbauer measurements confirm that nitrogen austenite is nonmagnetic. The anisotropy of Fe16N2 is small but detectable.