We measured Mössbauer spectra from bcc alloys of compositions near ${\mathrm{Fe}}_3$Al, ${\mathrm{Fe}}_3$Si, and ${\mathrm{Fe}}_3$Ge, and reanalyzed older data from ${\mathrm{Fe}}_3$Ga. All four alloys developed some D$0_3$ chemical order, and their Mössbauer spectra were qualitatively similar. The local (first-nearest-neighbor) could be distinguished from the nonlocal (beyond the first-nearest-neighbor) contributions to the ${}_{}{}^{57}{}_{}{}^{}\mathrm{Fe}$ isomer shifts from the solute atoms owing to differences in their hyperfine magnetic fields. The nonlocal isomer shift contributions correlated best to the valence of the solute atom, and not to the atomic volume. The local isomer shift contributions were best attributed to a loss of Fe 3d electrons at the solute sites.

• Received 2 September 1993

DOI:https://doi.org/10.1103/PhysRevB.49.6312