Vortex dynamics and the critical current density in NdFeAsO0.9F0.1 single crystals

The importance of type-II superconductors with strong pinning comes from their ability to carry large transport currents in the presence of a magnetic field. We report on the results of the bulk magnetization measurements in the superconducting state in clean single crystals of NdFeAsO0.9F0.1 at various temperatures. The zero-temperature superconducting critical current density, Jc, where the superconducting transition temperature Tc reaches a maximum of 45(1) kelvin, displays a remarkable high value. The field dependence of the critical current density was analyzed within the collective pinning model. A remarkably good agreement between the experimental results and theoretical δ1 pinning curve is obtained. This indicates that pinning in NdFeAsO0.9F0.1 crystal originates from spatial variation of the mean free path. Additionally, the normalized pinning force density, Fp, curves verses H/Hirr (Hirr is the irreversibility field) were scaled using the Dew-Hughes model. Our analysis suggests that point pinning alone cannot explain the observed field variation of Fp.