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

We present a Fe K$\beta$ x-ray emission spectroscopy study of local magnetic moments in various iron-based superconductors in their paramagnetic phases. Our findings show that a local magnetic moments exists in all samples studied: PrFeAsO, $\rm Ba(Fe,Co)_2As_2$, LiFeAs, Fe$_{1+x}$(Te,Se), and $\rm A_2Fe_4Se_5$ (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 pnictides samples have local moments of about 1$\mu_B$/Fe, while FeTe and $\rm K_2Fe_4Se_5$ families have much larger local moments of $\sim\!\!2 \mu_B$/Fe and $\sim\!\! 3.3 \mu_B$/Fe, respectively. Our results illustrate the importance of multi-orbital physics in describing magnetism of these compounds.