Composition Gradients in Ni–Fe Alloy Films Produced by Vapor Deposition from a Tungsten Boat

When an alloy film is produced by evaporation from a limited volume of material in a tungsten boat, differences in the vapor pressures of the constituents can produce different compositions through the thickness of the film. These composition changes can affect magnetic properties; e.g., it has been suggested that magnetization gradients produce anomalies in spin wave spectra. We have measured the variation of composition through the thickness of Ni–Fe films by moving a long substrate past a collimated source during deposition from a boat. It is observed that for a wide range of deposition temperatures and integrated thickness the results nearly coincide if all of the data are plotted as a function of normalized fractional thickness. For starting material of 80.89% Ni, evaporated to completion, the initial composition is 74% Ni and rises linearly to 81% Ni at 0.8 fractional thickness. A steeply rising exponential region follows. The origin of these regions will be discussed.