Dominant role of local-moment interactions in the magnetic ordering of iron pnictide superconductors: A comparative study of arsenides and antimonides from first principles

The magnetic properties of various iron pnictides are investigated using first-principles pseudopotential calculations. We consider three different families, LaFePnO, BaFe2 P n2, and LiFePn with Pn=As and Sb, and find that the Fe local spin moment and the stability of the stripe-type antiferromagnetic phase increases from As to Sb for all of the three families, with a partial gap formed at the Fermi energy. In the meanwhile, the Fermi-surface nesting is found to be enhanced from Pn=As to Sb for LaFePnO but not for BaFe2 P n2 and LiFePn. These results indicate that the local-moment interaction is the dominant factor over the Fermi-surface nesting in determining the stability of the magnetic phase in these materials and that the partial gap is an induced feature by a specific magnetic order.