Low-energy coherent Stoner-like excitations in CaFe2As2

Using linear-response density functional theory, magnetic excitations in the striped phase of CaFe2As2 are studied as a function of local-moment amplitude. We find a new kind of excitation: sharp resonances of Stoner-like (itinerant) excitations at energies comparable to the Neel temperature, originating largely from a narrow band of Fe d states near the Fermi level, and coexisting with more conventional (localized) spin waves. Both kinds of excitations can show multiple branches, highlighting the inadequacy of a description based on a localized spin model.