Muon spin relaxation studies of magnetic order and superfluid density in   antiferromagnetic NdOFeAs, BaFe2As2 and superconducting (Ba,K)Fe2As2
  Zero-field (ZF) muon spin relaxation ($\mu$SR) measurements have revealed static commensurate magnetic order of Fe moments in NdOFeAs below $T_{N} \sim 135$ K, with the ordered moment size nearly equal to that in LaOFeAs, and confirmed similar behavior in BaFe$_{2}$As$_{2}$. In single crystals of superconducting (Ba$_{0.55}$K$_{0.45}$)Fe$_{2}$As$_{2}$, $\mu$SR spectra indicate static magnetism with incommensurate or short-ranged spin structure in $\sim$ 70 % of volume below $T_{N} \sim$ 80 K, coexisting with remaining volume which exhibits superfluid-response consistent with nodeless gap below $T_{c}\sim 30$ K. 
A. A. Aczel, E. Baggio-Saitovitch, S. L. Budko, P.C. Canfield, J. P.   Carlo, G. F. Chen, Pengcheng Dai, T. Goko, W. Z. Hu, ...