Microscopic coexistence of superconductivity and antiferromagnetism in   underdoped Ba(Fe1-xRux)2As2
  We use $^{75}$As nuclear magnetic resonance (NMR) to investigate the local electronic properties of Ba(Fe$_{1-x}$Ru$_{x}$)$_2$As$_2$ ($x =$ 0.23). We find two phase transitions, to antiferromagnetism at $T_N \approx$ 60 K and to superconductivity at $T_C \approx$ 15 K. Below $T_N$, our data show that the system is fully magnetic, with a commensurate antiferromagnetic structure and a moment of 0.4 $\mu_B$/Fe. The spin-lattice relaxation rate $1/^{75}T_1$ is large in the magnetic state, indicating a high density of itinerant electrons induced by Ru doping. On cooling below $T_C$, $1/^{75}T_1$ on the magnetic sites falls sharply, providing unambiguous evidence for the microscopic coexistence of antiferromagnetism and superconductivity. 
Long Ma, G. F. Ji, Jia Dai, X. R. Lu, M. J. Eom, J. S. Kim, B.   Normand, Weiqiang Yu
cond-mat.supr-con cond-mat.str-el