Crystal structure and magnetic properties of α-Fe16N2 containing residual α-Fe prepared by low-temperature ammonia nitridation

Slight enhancement of saturation magnetization to 219 A m(2) kg(-1) was observed from 199 A m(2) kg(-1) for the original alpha-Fe on the intermediate nitrided mixture of alpha ''-Fe16N2 with residual alpha-Fe among the low temperature ammonia nitridation products under 5 T magnetic field at room temperature. The value changed not linearly against the yield as had been expected. Crystal structure refinement indicated that the phase similar to alpha ''-Fe16N2 had deviations on its lattice constants and positional parameters, compared to previously reported values for alpha ''-Fe16N2. Spin-polarized total energy calculations were performed using the projector-augmented wave method as implemented in the Vienna ab-initio simulation package (VASP) to calculate magnetic moment on the refined crystal structure of the intermediate alpha ''-Fe16N2. The calculations supported the observed magnetization enhancement in the intermediate nitridation product. (C) 2012 Elsevier Inc. All rights reserved.