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

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 individual magnetic moments in each orbital in the leading-order approximation in the nonlocal 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 J0 ' 0.20 eV, while for nickel we obtain J0 ' 1.2 eV. The considered method also allows one to describe the spin-wave dispersion at temperatures T ti TC, which is in agreement with the experimental data.