Magnetic moment evolution and spin freezing in doped BaFe(2)As(2)

Fe-K(β) X-ray emission spectroscopy measurements reveal an asymmetric doping dependence of the magnetic moments μ (bare) in electron- and hole-doped BaFe(2)As(2). At low temperature, μ (bare) is nearly constant in hole-doped samples, whereas it decreases upon electron doping. Increasing temperature substantially enhances μ (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.