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

TL;DR

This paper introduces a method based on the alloy analogy model to calculate temperature-dependent response functions in solids, effectively incorporating thermal vibrations and spin fluctuations, and compares results with experimental data.

Contribution

It presents a novel scheme combining the alloy analogy model with Monte Carlo spin configurations to accurately compute temperature-dependent magnetic and electrical properties.

Findings

The alloy analogy model reproduces Monte Carlo magnetic moments across models.

Response quantities are highly sensitive to spin fluctuation models.

Thermal vibrations and spin fluctuations both significantly affect conductivity and damping.

Abstract

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.