Magnetic exchange in $\alpha $-iron from the ab initio calculations in the paramagnetic phase

TL;DR

This study uses advanced ab initio methods to analyze magnetic exchange in paramagnetic alpha-iron, revealing the roles of different electronic states and non-quasiparticle effects in its magnetic properties.

Contribution

It introduces a detailed ab initio analysis of magnetic exchange in alpha-iron, highlighting the importance of non-quasiparticle states and hybridization effects, and proposes an effective spin-fermion model.

Findings

Both e_g and t_2g states contribute to magnetic moments below 1500K.

t_2g states deviate from Fermi-liquid behavior, affecting magnetic properties.

Hybridization between t_2g and e_g states drives exchange interactions.

Abstract

Applying the local density approximation (LDA) and dynamical mean field theory (DMFT) to paramagnetic $\alpha $-iron, we revisit a problem of theoretical description of its magnetic properties. The analysis of local magnetic susceptibility shows that at sufficiently low temperatures $T<1500K$, both, $e_{g}$ and $t_{2g}$ states equally contribute to the formation of the effective magnetic moment with spin S=1. The self-energy of t_{2g} states shows sizable deviations from Fermi-liquid form, which accompanies earlier found non-quasiparticle form of e_{g} states. By considering the non-uniform magnetic susceptibility we find that the non-quasiparticle form of $e_{g}$ states is crucial for obtaining ferromagnetic instability in $\alpha $-iron. The main contribution to the exchange interaction, renormalized by the effects of electron interaction, comes from the hybridization between $t_{2g}$ and $e_{g}$ states. We furthermore suggest the effective spin-fermion model for $\alpha $-iron, which allows us to estimate the exchange interaction from paramagnetic phase, which is in agreement with previous calculations in the ordered state within the LDA approaches.