Magnetic exchange in $\alpha $-iron from the ab initio calculations in   the paramagnetic phase
  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. 
P. A. Igoshev, A. V. Efremov, A. A. Katanin
cond-mat.str-el cond-mat.mtrl-sci