Mössbauer effect study of the magnetic state of iron atoms in Fe-Ni 36 wt.% Invar alloys

The⁵⁷Fe Mössbauer spectra of the Fe-Ni 36 wt.% Invar alloy at different temperatures (300-530 K) have been measured. The experimental results indicate that the hyperfine field distributions are characterized by dual peaks. The temperature dependence of the hyperfine field indicates that some iron atoms may transfer from the ferromagnetic state to the antiferromagnetic one with increasing temperature, and that the variation of the ratio of number N₀ of the iron atoms in the antiferromagnetic state to the number N_h in the ferromagnetic state with temperature will obey the thermodynamic relationship.