Magnetization Relaxation and Collective Vortex Pinning in the Fe-Based   Superconductor SmFeAsO_0.9F_0.1
  By measuring the dynamic and traditional magnetization relaxations we investigate the vortex dynamics of the newly discovered superconductor SmFeAsO_0.9F_0.1 with Tc = 55K. It is found that the relaxation rate is rather large reflecting a small characteristic pinning energy. Moreover it shows a weak temperature dependence in wide temperature region, which resembles the behavior of the cuprate superconductors. Combining with the resistive data under different magnetic fields, a vortex phase diagram is obtained. Our results strongly suggest that the model of collective vortex pinning applies to this new superconductor very well. 
Huan Yang, Cong Ren, Lei Shan, and Hai-Hu Wen