Mössbauer study of atomic order inNi3Fe. I. Determination of the long-range-order parameter

By means of Mössbauer spectroscopy we studied the structural order in a series of stoichiometric ${\mathrm{Ni}}_3$Fe foils, which had been given different heat treatments. The long-range-order parameter $\eta$ was determined with an accuracy of ±0.02 by analyzing the profiles of the outer lines of ${}_{}{}^{57}{}_{}{}^{}\mathrm{Fe}$ absorption spectra, recorded at room temperature. From the analysis it appeared that the hyperfine field at ${}_{}{}^{57}{}_{}{}^{}\mathrm{Fe}$ nuclei depends linearly on the numbers of iron atoms in the first and second neighboring shell, and that contributions from more distant atoms are negligible. Further anisotropic hyperfine interactions in ${\mathrm{Ni}}_3$Fe are small. A comparison with $\eta$ as determined from x-ray diffraction indicates that the wrongly placed atoms in partly ordered ${\mathrm{Ni}}_3$Fe are distributed at random over the lattice sites.