Mn local moments prevent superconductivity in iron-pnictides Ba(Fe 1-x   Mn x)2As2
  75As nuclear magnetic resonance (NMR) experiments were performed on Ba(Fe1-xMnx)2As2 (xMn = 2.5%, 5% and 12%) single crystals. The Fe layer magnetic susceptibility far from Mn atoms is probed by the75As NMR line shift and is found similar to that of BaFe2As2, implying that Mn does not induce charge doping. A satellite line associated with the Mn nearest neighbours (n.n.) of 75As displays a Curie-Weiss shift which demonstrates that Mn carries a local magnetic moment. This is confirmed by the main line broadening typical of a RKKY-like Mn-induced staggered spin polarization. The Mn moment is due to the localization of the additional Mn hole. These findings explain why Mn does not induce superconductivity in the pnictides contrary to other dopants such as Co, Ni, Ru or K. 
Y. Texier, Y. Laplace, P. Mendels, J. T. Park, G. Friemel, D. L. Sun,   D. S. Inosov, C. T. Lin, J. Bobroff
cond-mat.supr-con cond-mat.str-el