Calculating linear response functions for finite temperatures on the basis of the alloy analogy model

A scheme is presented that is based on the alloy analogy model and allows to account for thermal lattice vibrations as well as spin fluctuations when calculating response quantities in solids. Various models to deal with spin fluctuations are discussed concerning their impact on the resulting temperature dependent magnetic moment, longitudinal conductivity and Gilbert damping parameter. It is demonstrated that using the Monte Carlo (MC) spin configuration as an input, the alloy analogy model is capable to reproduce results of MC simulations on the average magnetic moment within all spin fluctuation models under discussion. On the other hand, response quantities are much more sensitive to the spin fluctuation model. Separate calculations accounting for either the thermal effect due to lattice vibrations or spin fluctuations show their comparable contributions to the electrical conductivity and Gilbert damping. However, comparison to results accounting for both thermal effects demonstrate violation of Matthiessen's rule, showing the non-additive effect of lattice vibrations and spin fluctuations. The results obtained for bcc Fe and fcc Ni are compared with the experimental data, showing rather good agreement for the temperature dependent electrical conductivity and Gilbert damping parameter

An ab initio investigation of how residual resistivity can decrease when an alloy is deformed

For a class of transition metal materials residual resistivity is observed to decrease when the materials are deformed and short-range order is removed. We investigate this counter-intuitive behavior with an ab initio theoretical study of the residual resistivity of several late transition metal-rich disordered alloys. The calculations are performed using the Korringa-Kohn-Rostoker (KKR) method applied to the Kubo-Greenwood formalism. The electronic effects arising from short-range ordering and clustering within the disorder are described using the non-local coherent-potential approximation (NL-CPA). We find a simple, general explanation of this K-state-like effect in terms of changes to the amplitude for d-electron hopping between majority late transition metal nearest-neighbor atoms at the Fermi energy. Copyright (C) EPLA, 201