NMR investigation of vortex dynamics in the Ba(Fe0.93Rh0.07)2As2 superconductor

75As NMR spin-lattice relaxation (1/T1) and spin-echo decay (1/T2) rate measurements were performed in a single crystal of Ba(Fe0.93Rh0.07)2As2 superconductor. Below the superconducting transition temperature Tc, when the magnetic field H is applied along the c axes, a peak in both relaxation rates is observed. Remarkably that peak is suppressed for H ⊥ c. Those maxima in 1/T1 and 1/T2 have been ascribed to the flux lines lattice motions and the corresponding correlation times and pinning energy barriers have been derived on the basis of a heuristic model. Further information on the flux lines motion was derived from the narrowing of 75As NMR linewidth below Tc and found to be consistent with that obtained from 1/T2 measurements. All the experimental results are described in the framework of thermally activated vortices motions.