Spin-Density Oscillations in Ferromagnetic Alloys. I. "Localized" Solute Atoms: Al, Si, Mn, V, and Cr in Fe

The internal magnetic fields and isomer shifts of ${\mathrm{Fe}}^{57}$ nuclei in a number of iron-rich bcc binary alloy systems were measured by the Mössbauer technique. The added solute atoms Al, Si, Mn, Cr, or V give structure to the individual lines of the spectra indicating that their effects are quite localized. These line shapes were analyzed by a computer program which interpreted them in terms of the effects of the solute atoms in the first five neighbor shells. It appears justifiable to attribute the observed hyperfine-field shifts in the FeAl series to the spatial variation of the spin polarization of the $4s$ conduction electrons around an Fe atom in pure iron. The observed $4s$ spin-polarization variation with distance had oscillations with a $k_F\simeq \mathrm{}(1.0-1.2)\mathrm{}\times {10}^8$ ${\mathrm{cm}}^{-1\mathrm{}}$ corresponding to 0.4-0.6 electrons/atom in the $4s$ conduction band. These oscillations are compared with those obtained by recent improved calculations of the indirect exchange polarization which take into account the full $k$ dependence of the conduction-electron wave functions. For all the alloy series reported here, internal field shifts at the first and second nearest neighbors decreased the internal field. This indicates that the $4s$ electrons produce an antiferromagnetic contribution to the magnetic coupling in iron. The average internal field of each alloy was also obtained, and for all the alloy series described here this quantity decreases more rapidly than the moment per Fe atom as a function of solute-atom concentration. The isomer shifts due to solute atoms in the first three neighbor shells are also reported.