Influence of the extra layer on the transport properties of NdFeAsO1-0.14F0.14 and FeSe0.88 superconductors from magneto dynamic analysis

In this letter, the electromagnetic response of the NdFeAsO 1-0.14F 0.14 (Tc = 49 K) superconductor system, characterized by FeAs and NdO alternating layers, has been compared with that of FeSe 0.88.We have studied the flux dynamics of these two systems by means of ac multi-harmonic magnetic susceptibility. The analysis shows that although characterized by larger thermal fluctuations due to its higher Tc, NdFeAsO 1-0.14F 0.14 exhibits a stronger pinning force relative to FeSe 0.88. The further Irreversibility Line (IL) analysis also points out that both superconductors have a 3D flux pinning behavior.We associate the stronger pinning force in the NdFeAsO 1-0.14F 0.14 structure to the presence of the extra NdO layer. Different pinning contributions can be associated to the structural stress associated to FeAs superconducting layers and/or to the Nd3+ ions magnetic moment (μ ∼ 3.6 μB) contribution on the flux cores. We will also show that these pinning are over imposed to a weak collective contribution due to the dopant F atoms. ©Springer Science+Business Media, LLC 2012.