Spin waves in the (0,pi) and (0,pi,pi) ordered SDW states of the t-t' Hubbard model: Application to doped iron pnictides

Spin waves in (0,pi) and (0,pi,pi) ordered spin-density-wave (SDW) states of the t-t' Hubbard model are investigated at finite doping. In the presence of small t', these composite ferro-antiferromagnetic (F-AF) states are found to be strongly stabilized at finite hole doping due to enhanced carrier-induced ferromagnetic spin couplings as in metallic ferromagnets. Anisotropic spin-wave velocities, spin-wave energy scale of around 200meV, reduced magnetic moment, and rapid suppression of magnetic order with electron doping x (corresponding to F substitution of O atoms in La O_{1-x} F_x Fe As or Ni substitution of Fe atoms in Ba Fe_{2-x} Ni_x As_2) obtained in this model are in agreement with observed magnetic properties of doped iron pnictides.