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Abstract: The effects of the Mo and Co on the magnetic properties and the characteristics of martensitic transformation of the Fe–Mn alloy have been investigated by scanning electron microscopy (SEM), transmission electron microscopy (TEM), differential scanning calorimeter (DSC), and Mössbauer spectroscopy. Experiments reveal that two types of thermal-induced martensites, ɛ(h.c.p.) and α′(b.c.c.) martensites, form in the as-quenched alloys and these transformations have athermal characters. The Mo or Co (5wt%) addition to the Fe-13%Mn alloy does not change coexistence of ɛ and α′ martensites between 10–15wt%Mn content. However, it stabilizes the parent phase leading to the depression of the transformation temperatures. In addition, Mössbauer spectra of the alloys reveal a paramagnetic character with a singlet for the γ(f.c.c.) austenite and ɛ martensite phases and a ferromagnetic character with a broad sextet for α′ martensite phase. The volume fractions of the phases change and the amount of α′ martensite increases significantly with the Mo or Co addition. Third element addition also influences internal magnetic field and particularly, the addition of the Mo considerably decreases the internal magnetic field in the Fe–Mn alloy. [Copyright &y& Elsevier]