LOCAL AND NONLOCAL ISOMER-SHIFTS IN BCC FE-X ALLOYS (X=AL,SI,GA,GE)

We measured Mossbauer spectra from bcc alloys of compositions near Fe3 Al, Fe3Si, and Fe3Ge, and reanalyzed older data from Fe3Ga. All four a lloys developed some D0(3) chemical order, and their Mossbauer spectra were qualitatively similar. The local (first-nearest-neighbor) could be distinguished from the nonlocal (beyond the first-nearest-neighbor) contributions to the Fe-57 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 w ere best attributed to a loss of Fe 3d electrons at the solute sites.