The effect of the Ge content on the paramagnetic-antiferromagnetic transition in γ-Fe-Mn alloys

The temperature T dependence of magnetic susceptibility chi in the range 77-600 K and the Mossbauer absorption spectra at 310 K were measured for gamma -Fe-30 at.% Mn alloys containing 2.01, 3.45, 5.63 and 8.73 at.% Ge. With increasing Ge content, the Neel temperature TN decreases linearly while chi increases markedly and becomes temperature dependent above TN, i.e., the Pauli paramagnetism of the alloys becomes a paramagnetism obeying the Curie-Weiss law. This behaviour of Fe-Mn-Ge is essentially similar to that of gamma -Fe-Mn alloys containing Al or Si. The behaviour of the chi -T curves as well as the Mossbauer spectra results reveal that the increase in Ge content has led to a decrease in the itinerant character of 3d electrons in gamma -Fe-Mn host alloys and to an increase in the localised net moment at the Fe atoms. These observations lead the authors to assume that alloying Fe-Mn with Ge alters the host density of states and consequently the Fermi level, which gives rise to a change in localised moment at Fe atoms. Finally, the Neel temperature of gamma -Fe-Mn host alloys as a function of the average electron concentration has been discussed in brief.