Magnetic moment evolution and spin freezing in doped BaFe${}_2$As${}_2$

Abstract

Fe-K${}_{\hat{I}}^2$ X-ray emission spectroscopy measurements reveal an asymmetric doping dependence of the magnetic moments $\hat{I}{¼}_{\text{bare}}$ in electron- and hole-doped BaFe${}_2$As${}_2$. At low temperature, $\hat{I}{¼}_{\text{bare}}$ is nearly constant in hole-doped samples, whereas it decreases upon electron doping. Increasing temperature substantially enhances $\hat{I}{¼}_{\text{bare}}$ in the hole-doped region, which is naturally explained by the theoretically predicted crossover into a spin-frozen state. Our measurements demonstrate the importance of Hund's coupling and electronic correlations, especially for hole-doped BaFe${}_2$As${}_2$, and the inadequacy of a fully localized or fully itinerant description of the 122 family of Fe pnictides.