Structural and magnetic features of the solid-state synthesis and martensitic transformations in Ni/Fe(0 0 1)/MgO(0 0 1) thin films

The results of the experimental study of phase transformations occurring in Ni/Fe(0 0 1)/MgO(0 0 1) thin films with 3Fe:1Ni atomic composition during annealing at temperatures up to 650 °C and cooling to liquid nitrogen temperature are presented. Comparative analysis of previous and current results suggests that the paramagnetic phase γpar present in the invar of Ni1−xFex alloys is the γ-Fe3Ni phase with the lattice parameter a=0.3600 nm. Measurements of magnetization of the samples in dependence of composition allowed one to determine a single-phase region of γpar phase existence in thin films limited by 75 at% Fe. It is shown that the temperature of γpar phase initiation during the solid-state synthesis coincides with the temperature AS of the reverse martensitic α′→γpar transition (AS=T0∼550 °C).