Strong local moment antiferromagnetic spin fluctuations in V-doped LiFeAs

We use neutron scattering to study Vanadium (hole)-doped LiFe 1− x V x As. In the undoped state, LiFeAs exhibits superconductivity at T c = 18 K and transverse incommensurate spin excitations similar to electron overdoped iron pnictides. Upon Vanadium doping to form LiFe 0.955 V 0.045 , the transverse incommensurate spin excitations in LiFeAs transform into longitudinally elongated ones in a similar fashion to that of potassium (hole)-doped Ba 0.7 K 0.3 Fe 2 As 2 but with dramatically enhanced magnetic scattering and elimination of superconductivity. This is different from the suppression of the overall magnetic excitations in hole-doped BaFe 2 As 2 and the enhancement of superconductivity near optimal hole doping. These results are consistent with density function theory plus dynamic mean field theory calculations, suggesting that Vanadium doping in LiFeAs may induce an enlarged effective magnetic moment S eff with a spin crossover ground state arising from the inter-orbital scattering of itinerant electrons.