The thin magnetic layer is permalloy (Fe0.20Ni0.80), sometimes alloyed with another element such as Cu. In a recent joint experimental/theoretical paper, we have compared some properties of of the Py_xCu_1-x alloy to measured data, and estimate the alloy scattering lifetime of the alloy.
The picture shows the alloy energy band structure of Py and Py0.8Cu0.2, computed with the Coherent Potential Approximation. Alloy scattering broadens out the energy bands, especially the conduction band, increasing the scattering rate. The scattering increases with Cu content. As explained in the paper, this can be simply interpreted in terms of misalignment of the transition metal d states