Anomalous Thickness Dependence of the Saturation Magnetization in Fe–Ni Invar Alloy Films

Abstract

Invar alloy films with the fcc structure were prepared using the vacuum evaporation technique. Using the thickness graded film in the alloy compositions of 21%NiFe and 36%NiFe, the thickness dependence of saturation magnetization was studied. As the film thickness decreases from 1000 A to 200 A, the saturation magnetization of 36%NiFe decreases monotonically and that of 21%NiFe initially increases down to 350 A, and finally decreases. The temperature dependence of the saturation magnetization of 21%NiFe shows very flatter one compared with that of the theoretical Brilloin function.
These results are supposed to be origniated not from the existence of the gradient of the composition but from the appearance of γ₂ phase through the interface interraction between the substrate and film.