Spin-disorder resistivity in Fe–Ni and Mn–Ni alloys

Abstract

Two series of fcc Fe100−xNix and Mn100−xNix alloys were prepared for the purpose of testing the theory of spin-disorder scattering. The original theory, as proposed by deGennes and Friedel, was valid in a strict sense only for pure metals. For a binary alloy A1−xBx, we have modified the theory so that the average local spin S̄ for the alloy is defined and well incorporated in the whole scheme. Experimentally speaking, we have measured the high-temperature (from 300 to 1100 K) electrical resistivity ρ and the low-temperature (at 5 K) saturation magnetization MS of the alloys. From the resistivity measurement, the spin-disorder resistivity at or above the Curie temperature ρmag was found, and from the magnetization measurement, S̄ could be determined for each alloy. In our theory, we can express the quantity ρmag/S̄(S̄+1) as a function of the nickel concentration x explicitly. Then, the ρmag/S̄(S̄+1) data from the Fe–Ni and Mn–Ni alloys were plotted versus x, and then fitted by the modified theory. Note, the former alloy is on the straight line of the Slater–Pauling curve and the latter shows marked deviations. We have reached a conclusion that |JsdFe|>|JsdNi|>|JsdMn|, where |JsdFe|, |JsdNi|, and |JsdMn| are the magnitudes of the s-d exchange interactions between the spin s of the 4s electron and the local spin Si at the iron, nickel, and manganese sites, respectively.