MOSSBAUER-SPECTROSCOPY OF FE60NI40 ALLOY-FILMS

Films of the alloy Fe60Ni40 are prepared by thermal evaporation of the alloy powder onto Al foils. Mossbauer spectra of the films on the Al substrate show a dominent central paramagnetic line during the first month after their preparation, which is attributed to the Fe;rich gamma' f.c.c. phase. The spectrum collected four months after preparation shows a 25% decrease in the relative intensity of the paramagnetic signal. However, the paramagnetic intensity drops by 65% upon removal of the film from the substrate, reaching a value close to that for the original alloy powder. This is interpreted as due to the atomic diffusion of Fe atoms from Fe-rich clusters into the surrounding Fe-Ni matrix, and the occurrence of a phase relaxation to a state similar to that of the original powder, implying that the relative proportion of the gamma' phase could be dictated by the chemical composition of the alloy.