Insight into the Slater-Pauling behavior of Permalloy-Cu alloys

Magnetic 3d transition alloys are of great importance, but a rigorous understanding of the magnetization for these systems remains elusive. While it is well-known that the average magnetic moment of 3d transition metal alloys obey Slater-Pauling, the oft-cited basis for our understanding of this ``law'' is suspect: The high-valence side of Slater-Pauling was originally explained by Slater via rigid-band theory (RBT), with the primary effect to be the filling of the minority d-band with valence electrons upon alloying. However, many ab-initio calculations do not support RBT since alloying affects the band-structure. We used X-ray magnetic circular dichroism to test the veracity of RBT as a model for Slater-Pauling behavior for Permalloy-Cu alloys, (Ni0.8Fe0.2)xCu1-x. We find that our data agrees with Slater-Pauling regarding average magnetic moments. Also, the dilution of Permalloy by Cu does result in some charge transfer from Cu to Ni/Fe, in qualitative agreement with RBT, but the charge transfer is inadequate to explain the dependence of spin moment on Cu concentration. Of equal importance is the decrease of exchange splitting due to the reduced number of magnetic neighbors.