Internal Magnetic Fields, Isomer Shifts, and Relative Abundances of the Various Fe Sites in FeSi Alloys

The "Mössbauer" technique was used to measure the internal magnetic fields and isomer shifts of ${\mathrm{Fe}}^{57}$ atoms residing at various sites in the FeSi series. The relative abundances of the various sites present in a given alloy were obtained by measuring the relative intensities of the components in the resolved spectrum of the alloy. Alloys with Si content varying from 0 to ∼27 at.% were studied. In the disordered region (<10 at.% Si) three different type sites were observed. These corresponded to Fe atoms having 8, 7, and 6 nearest-neighbor Fe atoms. The internal field decreased by $0.08 H_{\mathrm{Fe}}$ for each Si nearest neighbor. In the ordered region the alloys try to go into a ${\mathrm{Fe}}_3$Al type structure. Sites having 8 through 3 nearest-neighbor iron atoms were observed. For $A$-type sites (4 nearest-neighbor Fe atoms and 4 nearest-neighbor Si atoms at 25 at.% Si), the internal field decreased by $0.14 H_{\mathrm{Fe}}$ for each Si nearest neighbor. Over the whole series the isomer shift indicated that there was progressively less electronic charge density at the origin as the number of nearest-neighbor Si atoms increased. A measure of the relative intensities of the various magnetic field components in the spectra of an alloy series is shown to give direct evidence on the type of ordering. No tendency to form intermediate compounds other than ${\mathrm{Fe}}_3$Si was observed. An average internal magnetic field for each alloy could be obtained from the data. This average internal field does not vary in the same way as the magnetization on the FeSi series.