Investigation of Fluctuating Diamagnetism and Spin Dynamics in SmFeAsO1-xFx Superconductors

The superconducting iron-pnictides SmFeAsO1-xFx (x = 0.15 and x = 0.2) are studied by means of 19F-NMR spectroscopy and SQUID magnetometry. Fluctuating diamagnetism above Tc is briefly examined, stressing the analogy with the phenomenology in underdoped cuprates. The 19F relaxation rate allows us to infer an indirect magnetic coupling between Sm3+ moments, possibly involving conduction electrons in FeAs bands, with no appreciable effects on crossing the superconducting transition temperature. A comparison between the superconducting samples and the insulating SmOF, often present as spurious phase in SmFeAsO1-xFx pnictides, is also carried out. Relevant differences in the spin dynamics features are found.