Mössbauer study of the invar Fe–Ni and Fe–Ni–C alloys in magnetic field

F.C.C. Fe-30.3%Ni and Fe-30.5%Ni-1.5%C (wt.%) alloys were studied by means of Mossbauer spectroscopy in external magnetic field B ext=2.5, 5, 7 T parallel to the gamma-beam. It is shown that distribution of effective magnetic field in the alloys is broad and that carbon expands the range of B eff. The external magnetic field increases B eff in the Fe-Ni alloy and decreases it more evidently in the Fe-Ni-C alloy. Antiferromagnetic spin coupling along the ferromagnetic component is proposed to explain data.