Flux pinning mechanism in NdFeAsO0.82F0.18 superconductor: Thermally activated flux flow and charge carrier mean free path fluctuation pinning

TL;DR

This study investigates the flux pinning mechanisms in NdFeAsO0.82F0.18F superconductor, revealing charge carrier mean free path fluctuations as a key factor and demonstrating strong intrinsic pinning properties at high magnetic fields.

Contribution

It provides detailed analysis of flux pinning and flux flow in NdFeAsO0.82F0.18F, highlighting the delta-l pinning mechanism and thermal activation effects, which are less explored in this material.

Findings

Charge carrier mean free path fluctuations dominate pinning.

Thermally activated flux flow influences resistivity near Tc.

Stronger intrinsic pinning compared to Bi-2212 and MgB2 at high fields.

Abstract

The flux pinning mechanism of NdO0.82F0.18FeAs superconductor made under high pressure, with a critical temperature, Tc, of 51 K, has been investigated in detail in this work. The field dependence of the magnetization and the temperature dependence of the magnetoresistivity were measured in fields up to 13 T. The field dependence of the critical current density, Jc(B), was analyzed within the collective pinning model. A crossover field, Bsb, from the single vortex to the small vortex bundle pinning regime was observed. The temperature dependence of Bsb(T) is in good agreement with the delta-l pinning mechanism, i.e., pinning associated with fluctuations in the charge-carrier mean free path, l. Analysis of resistive transition broadening revealed that thermally activated flux flow is found to be responsible for the resistivity contribution in the vicinity of Tc. The activation energy U0/kB is 2000 K in low fields and scales as B (-1/3) over a wide field range. Our results indicate that the NdO0.82F0.18FeAs has stronger intrinsic pinning than Bi-2212 and also stronger than MgB2 for H > 8 T.