| Motivated by the itinerant magnetism of iron-based superconductors, we calculate magnetic excitations in the various ordered phases of these materials. In order to clarify the effect of the underlying orbital structure we compare two different scenarios in the antiferromagnetic phase: when the magnetic order either sets in on the on-site orbital level; or when it appears as an electron-hole pairing between different bands of electron and hole characters. In the superconducting phase a spin resonance emerges in the longitudinal channel below the superconducting transition temperature reflecting the unconventional symmetry of the order parameter. Assuming that in the coexistence regime the same electrons take part in the SDW, as well as, the SC ordering, we discuss the fate of the spin waves and the superconducting resonance. We compare our results with the available inelastic neutron scattering data and discuss the importance of the orbital degrees of freedom. |
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