Revealing the dual nature of magnetism in iron pnictides and iron chalcogenides using x-ray emission spectroscopy

We report a Fe K beta x-ray emission spectroscopy study of local magnetic moments in various iron-based superconductors in their paramagnetic phases. Local magnetic moments are found in all samples studied: PrFeAsO, Ba(Fe,Co)(2)As(2), LiFeAs, Fe(1+x) (Te,Se), and A(2)Fe(4)Se(5) (where A = K, Rb, and Cs). The moment size is independent of temperature or carrier concentration but varies significantly across different families. Specifically, all iron pnictide samples have local moments of about 1 mu(B)/Fe, while FeTe and K(2)Fe(4)Se(5) families have much larger local moments of similar to 2 mu(B)/Fe and similar to 3.3 mu(B)/Fe, respectively. Our results illustrate the importance of multiorbital physics in describing magnetism of these compounds.