(${\mathrm{Fe}}_{100\mathrm{-}\mathit{x}}$${\mathrm{Cr}}_{\mathit{x}}$${)}_{100\mathrm{-}\mathit{y}}$${\mathrm{Sn}}_{\mathit{y}}$ alloys with 42.0≤x≤44.7 and 0≤y≤5.6 were annealed at 700 °C for a period of up to 1000 h in order to cause a transformation of the α phase into the σ phase. Room temperature ${}_{}{}^{57}{}_{}{}^{}\mathrm{Fe}$ Mössbauer spectra registered on the samples consist of a magnetic subspectrum, related to the α phase, and a nonmagnetic subspectrum, related to the σ phase. Evidence is found that the isomer shift of the nonmagnetic subspectrum changes continuously with the amount of its relative contribution in the spectrum and it reaches the value characteristic of a pure σ phase only when its contribution in the two-phase sample is larger than about 30%.

• Received 24 September 1992

DOI:https://doi.org/10.1103/PhysRevB.47.12257