The role of Hund's coupling in the stabilization of the (0, π) ordered spin density wave state within the minimal two-band model for iron pnictides

Spin wave excitations and the stability of the (0, π) ordered spin density wave (SDW) state are investigated within the minimal two-band model for iron pnictides including a Hund's coupling term. The SDW state is shown to be stable in two distinct doping regimes-for finite hole doping in the lower SDW band for small second-neighbour hoppings, and for low electron doping in the upper SDW band for comparable first-neighbour and second-neighbour hoppings. In both cases, Hund's coupling strongly stabilizes the SDW state due to the generation of additional ferromagnetic spin couplings involving the inter-orbital part of the particle-hole propagator. The spin wave energies for the two-band model are very similar to the one-band t-t' Hubbard model results obtained earlier, and are in agreement with the findings from inelastic neutron scattering studies of iron pnictides. (fast track communication)