Hyperfine Fields in Dilute Alloys of Co in Fe

Spin-echo NMR spectra of ⁵⁷Fe and ⁵⁹Co in Fe alloys with 0.8, 2.6, 3.3, and 6 at.% Co have been decomposed to determine the influence of Co atoms on nearby Fe and Co hyperfine fields as a function of radial separation. Of the possible alternatives, the preferable solution of this long-standing question is similar, for the Fe sites, to that of Wertheim, Buchanan, and Wernick, but with second-nearest-neighbor effects only one-half as great. The model is interpreted in terms of an oscillatory radial variation affecting all sites, combined at Fe sites with changes in local moments to yield an over-all monotonic variation in hyperfine field with distance from Co atoms.