Magnetic Properties of Layered Iron-Nickel Films

Abstract

A study of layered vacuum-deposited Fe–Ni films was made with varied layer thickness (15 to 180 Å) and deposition temperature (300° and 350°C); average film composition was held to a nominal value of 25% Fe. Magnetic property measurements included total flux, coercivity, magnetostriction, anisotropy field, and dispersion. Composition was determined by x-ray fluorescence and physical thickness by inter-ferometry. As expected, a lower limit of layer thickness (∼20 Å for 300°C substrates, ∼30 Å for 350°C substrates) has been observed below which the films have properties comparable to the nominally homogeneous films from a normal evaporation. At the other end of the range, a thickness is reached where interdiffusion of layers is negligible and further increase in layer thickness produces negligible change in properties. Variation of properties between these two extremes of layer thickness was used to obtain information about diffusion rates in the films and the effect of composition inhomogeneities on magnetic properties. Experimental results indicate that the equivalent rate constant associated with diffusion during deposition is consistent with a vacancy or surface mechanism and differs widely from high-temperature diffusion constants. Of the magnetic properties measured, dispersion and magnetostriction yield the most significant information regarding the relationship between magnetic properties and the extent of interdiffusion. The results show that composition homogeneity normal to the film surface will result only when the source vapor has the correct composition when averaged over any time interval corresponding to a film thickness no greater than 20–30 Å.