19F NMR study of the coupling between 4f and itinerant electrons in the pnictide superconductors SmFeAsO1-xFx (0.15<x<0.2)

F-19 NMR measurements in SmFeAsO1-xFx, for 0.15 < x < 0.2, are presented. The nuclear spin-lattice relaxation rate 1/T-1 increases upon cooling with a trend analogous to the one already observed in CeCu5.2Au0.8, a quasi-two-dimensional heavy-fermion intermetallic compound with an antiferromagnetic ground state. In particular, the behavior of the relaxation rate either in SmFeAsO1-xFx or in CeCu5.2Au0.8 can be described in the framework of the self-consistent renormalization theory for weakly itinerant electron systems. Remarkably, no effect of the superconducting transition on F-19 1/T-1 is detected, a phenomenon which can hardly be explained within a single band model.