Magnetization relaxation and collective vortex pinning in the Fe-based superconductor SmFeAsO0.9F0.1

By measuring the dynamic and traditional magnetization relaxations we investigate the vortex dynamics of the recently discovered superconductor SmFeAsO0.9F0.1 with T-c = 55 K. 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. Combined with the resistivity 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 superconductor very well.