Search for 2γ states in FCC iron alloys by investigation of the ⁵⁷Fe isomer shift in the paramagnetic state

The authors report on ⁵⁷Fe Mossbauer isomer shift measurements of Fe_0.64Ni_0.36, Fe_0.68Ni_0.32 and Fe_0.60Ni_0.20 FCC Fe alloys in the temperature range from 13 to 1010K. The Weiss 2 gamma -states model and a simple 'volume model' have been fitted to the experimental data in order to explain the observed temperature dependence of the isomer shift. To separate the isomer shift from the measured centre-of-gravity shifts of the spectra, the authors used the Debye approximation of the second-order Doppler shift. The Debye temperatures were assumed to be dependent on temperature.