NMR investigation of vortex dynamics in 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 || ab. 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 an 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. 
L. Bossoni, P. Carretta, A. Thaler, P.C. Canfield
cond-mat.supr-con