Composition dependence of the Néel temperature and the entropy of the magnetic transition in the fcc phase of Fe-Mn and Fe-Mn-Co alloys

A key feature of the fcc-to-hcp martensitic transformation (MT) in Fe-Mn based alloys is that the fcc structure is strongly stabilized by a paramagnetic-to-antiferromagnetic ordering reaction, which partially or completely inhibits the MT. In order to treat this phenomenon in thermodynamic terms it is necessary to account for the composition dependence of the Néel temperature (TN) of the alloy and the entropy change (ΔSmg) associated to the loss of the antiferromagnetic ordering. In the present work the composition dependence of these properties in Fe-Mn and Fe-Mn-Co alloys have been established by performing systematic measurements of the heat capacity. The current results are critically compared with experimental data from the literature, as well as estimates and correlations based on previous analyses by the present authors. The relevance of the reported data for the understanding of the fcc-to-hcp MT in the Fe-Mn and Fe-Mn-Co alloys is highlighted.