Muon-spin rotation studies of SmFeAsO_0.85 and NdFeAsO_0.85   superconductors
  Measurements of the in-plane magnetic field penetration depth \lambda_{ab} in Fe-based superconductors with the nominal composition SmFeAsO_0.85 (T_c\simeq52K) and NdFeAsO_0.85 (T_c\simeq51K) were carried out by means of muon-spin-rotation. The absolute values of \lambda_{ab} at T=0 were found to be 189(5)nm and 195(5)nm for Sm and Nd substituted samples, respectively. The analysis of the magnetic penetration depth data within the Uemura classification scheme, which considers the correlation between the superconducting transition temperature T_c and the effective Fermi temperature T_F, reveal that both families of Fe-based superconductors (with and without fluorine) falls to the same class of unconventional superconductors. 
Rustem Khasanov, Hubertus Luetkens, Alex Amato, Hans-Henning Klauss,   Zhi-An Ren, Jie Yang, Wei Lu, and Zhong-Xian Zhao