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

Abstract

We report a Fe K$\ensuremath{\beta}$ 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, $\mathrm{Ba}{(\mathrm{Fe},\mathrm{Co})}_{2}{\mathrm{As}}_{2}$, LiFeAs, Fe${}_{1+x}$(Te,Se), and ${\mathrm{A}}_{2}{\mathrm{Fe}}_{4}{\mathrm{Se}}_{5}$ (where $\text{A}=\text{K}$, 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${\ensuremath{\mu}}_{B}$/Fe, while FeTe and ${\mathrm{K}}_{2}{\mathrm{Fe}}_{4}{\mathrm{Se}}_{5}$ families have much larger local moments of $\ensuremath{\sim}2{\ensuremath{\mu}}_{B}$/Fe and $\ensuremath{\sim}3.3{\ensuremath{\mu}}_{B}$/Fe, respectively. Our results illustrate the importance of multiorbital physics in describing magnetism of these compounds.