Comparison of model predictions with the measured Fe-site spin and charge-density changes in $\alpha$-iron: Mössbauer-effect study of ${\mathrm{Fe}}_{1-x}{\mathrm{Ge}}_x$ alloys

Using the Mössbauer effect we studied the influence of substituting Fe atoms by Ge atoms on the hf fields and isomer shifts for a series of ${\mathrm{Fe}}_{1-x}{\mathrm{Ge}}_x$ alloys containing up to about 9 at.% Ge. From the linear correlations between the hf fields and corresponding isomer shifts we calculated the hf coupling constants: ${\alpha }_0=460\mathrm{}$ kOe per $s$ electron for the non-localized electrons, ${\alpha }_{1,2}=780\mathrm{}$ kOe per $s$ electron for the electrons localized within the first two neighbor shells, $\overline{\alpha }=275\mathrm{}$ kOe per $s$ electron the average value. Using these hf coupling constants and assuming the linear correlation between the average hf field and the average number of Ge atoms within the first two neighbor shells, we calculated the change of spin (charge) density at the Fe site caused by one Ge atom per unit cell, $\eta$, to be equal to -0.21. This agrees well with the model of Stearns, but disagrees with those of Friedel and Miedema.