The effect of austenitization heat treatment on magnetic properties was examined by means of M?ssbauer spectroscopy on an Fe-40wt/Ni-2wt/Mn alloy. The morphology of the alloy was obtained by using scanning electron microscopy (SEM) under dif-ferent heat treatment conditions. The magnetic behavior of the non heat-treated alloy is ferromagnetic. A mixed magnetic structure including both paramagnetic and ferromagnetic states was obtained at 800°C after 6 and 12 h heat treatments. In addition, the magnetic structure of the heat-treated alloy at 1150°C for 12 h was ferromagnetic. With the volume fraction changing, the effective hyperfine field of the ferromagnetic austenite phase and isomery shift values were also determined by M?ssbauer spectroscopy. The effect of austenitization heat treatment on magnetic properties was examined by means of Mössbauer spectroscopy on an Fe-40wt / Ni-2wt / Mn alloy. The morphology of the alloy was obtained by scanning electron microscopy (SEM) under dif-ferent heat treatment conditions. The magnetic behavior of the non heat-treated alloy is ferromagnetic. A mixed magnetic structure including both paramagnetic and ferromagnetic states was obtained at 800 ° C after 6 and 12 h heat treatments. In addition, the magnetic structure of the heat With the volume fraction changing, the effective hyperfine field of the ferromagnetic austenite phase and isomery shift values ​​were also determined by Mössbauer spectroscopy.