Cold work stored energy effect on the magnetic moment vs. temperature curve of Fe and of a Fe64Ni36 alloy

It is shown that lattice distortions introduced by cold work modify by a small, but not negligible amount the shap of the curve of the magnetic moment σsvs. temperature T, and the value of the Curie temperature Tcin ferromagnetic materials. Following some previous results relative to pure Ni, the cases of pure Fe and of a Fe64 Ni36 alloy, close to the Invar composition, are examined. The change of Tcobserved after cold work can be explained by taking into account the dependence of the Curie temperature upon strain. The overall slight change of the σsvs. T curve due to cold work can be accounted for by considering this curve as resulting from the sum of different ideal Brillouin curves, relative to small regions of the material characterized by different Tc´s, depending on the local lattice deformation. In the case of the Fe64 Ni36 alloy, the observed modifications after cold work of Tcand of the σsvs. T curve may also be due to some change of the local short range order.