Strong local moment antiferromagnetic spin fluctuations in V-doped LiFeAs

Zhuang Xu, Guangyang Dai, Yu Li, Zhiping Yin, Yan Rong, Long Tian, Panpan Liu, Hui Wang, Lingyi Xing, Yuan Wei, Ryoichi Kajimoto, Kazuhiko Ikeuchi, D. L. Abernathy, Xiancheng Wang, Changqing Jin,  Xingye Lu, Guotai Tan &  Pengcheng Dai 

Abstract

We use neutron scattering to study Vanadium (hole)-doped LiFe_1−xV_xAs. 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_0.955V_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_0.7K_0.3Fe₂As₂ but with dramatically enhanced magnetic scattering and elimination of superconductivity. This is different from the suppression of the overall magnetic excitations in hole-doped BaFe₂As₂ 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.