Impurity effects on spin dynamics in magnetic and superconducting iron pnictides and chalcogenides

In this article, we summarize the effects of magnetic and nonmagnetic impurities on the spin dynamics in Fe-based superconductors and their parent compounds. The effects of chemical substitution, vacancies, and disorder on the suppression or stabilization of superconductivity and spin-density-wave phases are reviewed in the context of recent neutron-spectroscopy measurements of spin excitations. We also present new results on the structure of magnetic fluctuations in BaFe2As2 single crystals doped with Mn local moments and discuss them in relationship to the previously reported (π,π) branch of checkerboard magnetic excitations.