HYPERFINE-FIELD STUDIES OF FE3AL AND FE3-XCRXAL ALLOYS

Measurements of hyperfine fields have been performed on ordered and disordered Fe3Al alloys and disordered Fe3-xCrxAl alloys for 0 less-than-or-equal-to x less-than-or-equal-to 1 with use of a Fe-57 Mossbauer technique. The Curie temperatures of all the samples were measured with use of the zero-velocity thermal-scan method. The Curie temperature decreases linearly with increasing chromium concentration. Mossbauer spectra of the samples show the presence of a paramagnetic peak coexisting with the hyperfine structure for x greater-than-or-equal-to 0.5. The spectra fitted with a hyperfine-field distribution show the presence of two hyperfine-field components. The lower of these in disordered Fe3Al is assigned to have 5 nearest-neighbor Al atoms and the higher-field one to have 2-3 nearest-neighbor Al atoms. A systematic replacement of Fe with Cr shows a linear decrease with increasing Cr concentration for both field components. The change in the lower field is only 65 kOe while that in the higher one is 120 kOe over the entire Cr-concentration range. The rapid decrease in the high-field component with increasing Cr concentration points to the fact that despite the considerable disorder which exists, Cr preferentially substitutes for iron at sites having 2-3 nearest-neighbor Al atoms.