Evidence for a high-spin Fe state in fcc Fe 1- xNi x thin films in the invar region

Abstract

Fe 1- x Ni x alloy films with compositions in the Invar region (0.32 < x < 0.39) were prepared by simultaneous co-deposition of Ni and Fe under uhv conditions onto quatrz crystal substrates. The structure of the films was obtained by X-ray diffraction, the composition by electronprobe microanalysis (EPMA). The temperature and field dependence of the magnetization M( B, T) was measured for 0 T < B < 1 T between 4.2 and 300 K. After investigating the structural and magnetic properties of the as-prepared Fe 1- x Ni x electron Mössbauer spectra (CEMS) were taken at room temperature for each Fe 1- x Ni x film as-prepared and after annealing It is possible to achieve Fe 1- x Ni x films as-prepared with pure fcc-structure and also mixtures of bcc and fcc phases. As-prepared films show, in contrast to the behavior of bulk Fe - x Ni x samples, high magnetic saturation moments M s and and large mean hyperfine-fields B̄ hf which follow the Slater-Pauling curve. After annealing the films exhibit bulk behavior. We conclude that Fe 1- x Ni x films as prepared are in a magnetic state of the fcc-phase which is probably related to the occurence of γ 2-Fe. By annealing the films these states convert into the metastable γ-state of the fcc phase with corresponding changes of the magnetic moment and the mean hyperfine field BB̄ hf.