The role of orbital order in the stabilization of the (π, 0) ordered magnetic state in a minimal two-band model for iron pnictides

Abstract

Spin wave excitations and stability of the (π, 0) ordered magnetic state are investigated in a minimal two-band itinerant-electron model for iron pnictides. Presence of hopping anisotropy generates a strong ferro-orbital order in the dxz and dyz Fe orbitals in the (π, 0) state. The orbital order sign is as observed in experiments. The induced ferro-orbital order strongly enhances the spin wave energy scale and stabilizes the magnetic state by optimizing the strength of the emergent antiferromagnetically and ferromagnetically spin couplings through optimal band fillings in the two orbitals. The calculated spin-wave dispersion is in quantitative agreement with neutron scattering measurements. Finite inter-orbital Hund's coupling is shown to further enhance the spin wave energies state by coupling the two magnetic sub-systems. A more realistic two-band model with less hopping anisotropy is also considered, which yields not only the circular hole pockets but also correct ferro-orbital order and emergent F spin coupling.