Glassy Transition in the Vortex Lattice of Ba(Fe0.93Rh0.07)2As2   superconductor, probed by NMR and ac-susceptibility
  By using Nuclear Magnetic Resonance and ac-susceptibility, the characteristic correlation times for the vortex dynamics, in an iron-based superconductor, have been derived. Upon cooling, the vortex dynamics displays a crossover consistent with a vortex glass transition. The correlation times, in the fast motions regime, merge onto a universal curve which is fit by the Vogel-Fulcher law, rather than by an Arrhenius law. Moreover, the pinning barrier shows a weak dependence on the magnetic field which can be heuristically justified within a fragile glass scenario. In addition, the glass freezing temperatures obtained by the two techniques merge onto the de Almeida-Thouless line. Finally the phase diagram for the mixed phase has been derived. 
L. Bossoni, P. Carretta, M. Horvati\'c, M. Corti, A. Thaler, P. C.   Canfield
cond-mat.supr-con cond-mat.str-el