Cooperative order in the weakly magnetic domain of   LaFeAsO$_{1-x}$F$_{x}$ near the doping phase boundary
  Spatial phase separation into mesoscopic domains of non-magnetic [superconducting (SC) below Tc = 25.5 K] and two kinds of magnetic phases, one showing disordered spin density wave (d-SDW) order and another associated with glassy weak magnetism (WM), are observed below ~100 K by muon spin rotation (muSR) in LaFeAsO1-xFx for x = 0.057(3) which is near the boundary of these phases on the doping phase diagram. In contrast to the competing order observed in the regular SDW phase of Ba(Fe1-xCox)2As2, the WM domain exhibits cooperative coupling of superconducting and magnetic order parameters as inferred from strong diamagnetism and associated negative shift of muSR frequency just below Tc. 
M. Hiraishi, R. Kadono, M. Miyazaki, I. Yamauchi, A. Koda, K. M.   Kojima, M. Ishikado, S. Wakimoto, and S. Shamoto
cond-mat.str-el