  The evolution of 75As NMR parameters with composition and temperature was
probed in the Ba(Fe1-xRux)2As2 system where Fe is replaced by isovalent Ru.
While the Ru-end member was found to be a conventional Fermi liquid, the
composition (x=0.5) corresponding to the highest Tc (20K) in this system shows
an upturn in 75As 1/T1T below about 80 K evidencing the presence of
antiferromagnetic (AFM) fluctuations. These results are similar to those
obtained in another system with isovalent substitution BaFe2(As1-xPx)2 [Y.
Nakai, T. Iye, S. Kitagawa, K. Ishida, H. Ikeda, S. Kasahara, H. Shishido, T.
Shibauchi, Y. Matsuda, and T. Terashima, Phys. Rev. Lett. 105, 107003 (2010)]
and point to the possible role of AFM fluctuations in driving
superconductivity.
