Exchange interactions in iron and nickel: DFT+DMFT study in paramagnetic phase

TL;DR

This study develops a method within DFT+DMFT to calculate magnetic exchange interactions in paramagnetic iron and nickel, successfully matching experimental spin-wave data and providing insights into their magnetic properties.

Contribution

The paper introduces a generalized approach to evaluate magnetic exchange interactions in paramagnetic metals using DFT+DMFT, extending previous methods and applying it to iron and nickel.

Findings

Calculated exchange interactions: ~0.20 eV for iron, ~1.2 eV for nickel.

Method describes spin-wave dispersion at temperatures near T_C.

Results align with experimental magnetic data.

Abstract

We analyze possible ways to calculate magnetic exchange interactions within the density functional theory plus dynamical mean-field theory (DFT+DMFT) approach in the paramagnetic phase. Using the susceptibilities obtained within the ladder DMFT approach together with the random phase approximation result for the Heisenberg model, we obtain bilinear exchange interactions. We show that the earlier obtained result of Stepanov et al. [Phys. Rev. Lett. 121, 037204 (2018); Phys. Rev. B 105, 155151 (2022)] corresponds to considering individual magnetic moments in each orbital in the leading-order approximation in the non-local correlations. We consider a more general approach and apply it to evaluate the effective magnetic parameters of iron and nickel. We show that the analysis, based on the inverse orbital-summed susceptibilities, yields reasonable results for both, weak and strong magnets. For iron we find, in the low-temperature limit, the exchange interaction $J_0\simeq 0.20$ eV, while for nickel we obtain $J_0\simeq 1.2$ eV. The considered method also allows one to describe the spin-wave dispersion at temperatures $T\sim T_C$, which is in agreement with the experimental data.