Effects of Atomic Configurational Changes on Hyperfine Interactions in Concentrated Iron-Cobalt Alloys

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Abstract
Room temperature 57Fe Mössbauer spectra were taken on atomically ordered and disordered iron‐cobalt samples as a function of composition between 25 and 75 at.% cobalt. The degree of long‐range order was determined in selected samples using neutron diffraction. The maximum values of the effective field (He) and isomer shift (I.S.) occur at 25 at.% cobalt where He=−365.5±0.5 kOe and I.S. = +0.037±0.005 mm/sec (relative to pure iron). In the composition range studied increasing the number of cobalt neighbors to an iron atom either by ordering or by increasing the cobalt concentration decreases both I.S. and He. The maximum decrease with ordering of I.S., He, and the line widths occurs at 50 at.% cobalt, where the decrease is about 0.02 mm/sec for I.S. and 10 kOe for He. These results indicate that local atomic configurations play a significant role in the competition between positive and negative contributions to He. The data suggest a positive spin polarization contribution at the nucleus.

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