Coexistence and competition of the short-range incommensurate   antiferromagnetic order with superconductivity in BaFe2-xNixAs2
  Superconductivity in the iron pnictides develops near antiferromagnetism, and the antiferromagnetic (AF) phase appears to overlap with the superconducting phase in some materials such as BaFe2-xTxAs2 (where T = Co or Ni). Here we use neutron scattering to demonstrate that genuine long-range AF order and superconductivity do not coexist in BaFe2-xNixAs2 near optimal superconductivity. In addition, we find a first-order-like AF to superconductivity phase transition with no evidence for a magnetic quantum critical point. Instead, the data reveal that incommensurate short-range AF order coexists and competes with superconductivity, where the AF spin correlation length is comparable to the superconducting coherence length. 
Huiqian Luo, Rui Zhang, Mark Laver, Zahra Yamani, Meng Wang, Xingye   Lu, Miaoyin Wang, Yanchao Chen, Shiliang Li, Sung Chan...
cond-mat.supr-con cond-mat.str-el