Changes in the electronic structure of iron induced by substitutional impurity W atoms

By means of Mössbauer-effect spectroscopy, we study changes in the electronic structure of iron induced by substitutional impurity W atoms in a series of ${\mathrm{Fe}}_{1-x}{\mathrm{W}}_x$ alloys containing up to about 9 at.% W. From the measured changes of the hyperfine (hf) fields and isomer shifts, and based on the correlations between the hf fields and isomer shifts as well as between the average hf field and the average number of W atoms in the two-shell environment of the Fe nuclei, we deduce that W atoms increase the Fe-site spin (charge) density when situated within the first two shells and decrease it when situated outside the first two shells. The average effect of this oscillatory behavior is that the average spin density follows the simple dilution behavior while the average charge density remains constant. We can account for this behavior by postulating that the majority spins flip into the minority-spin state at a constant rate of $\frac{1}{2}{\sigma }_{\mathrm{Fe}}, {\sigma }_{\mathrm{Fe}}$ being the net $s$-electron spin polarization in the nuclear volume of pure Fe. Finally, we evaluate the average change of the spin density caused by one W atom per unit cell, $\eta$, and find that it is consistent with the model predictions by Stearns [Phys. Rev. 147, 439 (1966)] and by Miedema [J. Less-Common Met. 32, 1117 (1973)].