Electronic transport in ferromagnetic alloys and the Slater-Pauling Curve

TL;DR

This study uses ab-initio calculations to explain the anomalous residual resistivity behavior in Fe-Cr alloys, revealing the role of minority spin electrons and suggesting similar effects in related alloys along the Slater-Pauling curve.

Contribution

The paper provides a theoretical explanation for the resistivity plateau in Fe-Cr alloys using KKR and Kubo-Greenwood methods, linking electronic structure to transport properties.

Findings

Resistivity increases linearly with Cr concentration up to 10% then plateaus.

Minority spin electrons dominate conductivity, causing the resistivity plateau.

Similar resistivity behavior is predicted for Fe-V alloys on the same Slater-Pauling branch.

Abstract

Experimental measurements of the residual resistivity $\rho(x)$ of the binary alloy system Fe$_{1-x}$Cr$_x$ have shown an anomalous concentration dependence which deviates significantly from Nordheim's rule. In the low ($x < 10%$) Cr concentration regime the resistivity has been found to increase linearly with $x$ until $\approx$ 10% Cr where the resistivity reaches a plateau persisting to $\approx$ 20% Cr. In this paper we present $ab$-$initio$ calculations of $\rho(x)$ which explain this anomalous behavior and which are based on the Korringa-Kohn-Rostoker (KKR) method in conjunction with the Kubo-Greenwood formalism. Furthermore we are able to show that the effects of short-range ordering or clustering have little effect via our use of the nonlocal coherent-potential approximation (NL-CPA). For the interpretation of the results we study the alloys' electronic structure by calculating the Bloch spectral function particularly in the vicinity of the Fermi energy. From the analysis of our results we infer that a similar behavior of the resistivity should also be obtained for iron-rich Fe$_{1-x}$V$_x$ alloys - an inference confirmed by further explicit resistivity calculations. Both of these alloy systems belong to the same branch of the famous Slater-Pauling plot and we postulate that other alloy systems from this branch should show a similar behavior. Our calculations show that the appearance of the plateau in the resistivity can be attributed to the dominant contribution of minority spin electrons to the conductivity which is nearly unaffected by increase in Cr/V concentration $x$ and we remark that this minority spin electron feature is also responsible for the simple linear variation of the average moment in the Slater-Pauling plot for these materials.