Magnetic exchange in α -iron from ab initio calculations in the paramagnetic phase

Abstract

Applying the local density approximation (LDA) and dynamical mean field theory to paramagnetic α-iron, we reinvestigate the origin of its ferromagnetism. The analysis of local magnetic susceptibility shows that at sufficiently low temperatures T<1500 K, both eg and t2g states equally contribute to the formation of the effective magnetic moment with spin S=1. The self-energy of t2g states shows sizable deviations from Fermi-liquid form, which accompany earlier found nonquasiparticle form of eg states. By considering the nonuniform magnetic susceptibility we find that the nonquasiparticle form of eg states is crucial for ferromagnetic instability in α-iron. The main contribution to the exchange interaction, renormalized by the effects of electron interaction, comes from the hybridization between t2g and eg states. We furthermore suggest the effective spin-fermion model for α-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. © 2015 American Physical Society.