Comparative study of the electronic and magnetic properties of BaFe2As2 and BaMn2As2 using the Gutzwiller approximation

To elucidate the role played by the transition-metal ion in the pnictide materials, we compare the electronic and magnetic properties of BaFe2As2 with BaMn2As2. To this end we employ the LDA+Gutzwiller method to analyze the mass renormalizations and the size of the ordered magnetic moment of the two systems. We study a model that contains all five transition-metal 3d orbitals together with the Ba 5d and As 4p states (ddp-model) and compare these results with a downfolded model that consists of Fe/Mn d states only (d-model). Electronic correlations are treated using the multiband Gutzwiller approximation. The paramagnetic phase has also been investigated using the LDA+Gutzwiller method with electron density self-consistency. The renormalization factors for the correlated Mn 3d orbitals in the paramagnetic phase of BaMn2As2 are shown to be generally smaller than those of BaFe2As2, which indicates that BaMn2As2 has stronger electron correlation effect than BaFe2As2. The screening effect of the main As 4p electrons to the correlated Fe/Mn 3d electrons is evident by the systematic shift of the results to the larger Hund’s rule coupling J side from the ddp-model compared with those from the d-model. A gradual transition from paramagnetic state to the antiferromagnetic ground state with increasing J is obtained for the models of BaFe2As2 which has a small experimental magnetic moment, while a rather sharp jump occurs for the models of BaMn2As2, which has a large experimental magnetic moment. The key difference between the two systems is shown to be the d-level occupation. BaMn2As2, with approximately five d electrons per Mn atom, is for the same values of the electron correlations closer to the transition to a Mott insulating state than BaFe2As2. Here an orbitally selective Mott transition, required for a system with close to six electrons, only occurs at significantly larger values for the Coulomb interactions.