Strong pinning in the hole-doped pnictide superconductor La0.34Na0.66Fe2As2

Abstract

We present magnetization studies as a function of time, temperature, and magnetic field for H ∥ c-axis, in a hole-doped pnictide superconductor, La0.34Na0.66Fe2As2, with Tc≈27K. The obtained vortex phase-diagram shows that the magnetic irreversibility line is very close to the mean-field superconducting transition line, similar to the low Tc superconductors, evidencing a strong pinning behavior. The irreversibility line does not follow a power law behavior with (Tc−T); however, it is well described using an expression developed in the literature, considering the effect of disorder in the system. The critical current density estimated using the Bean critical-state model is found to be of the order of 105A/cm2 below 12 K in the limit of zero magnetic field. A plot of the normalized pinning force density as a function of the reduced magnetic field at different temperatures shows good scaling, and the analysis suggests that the vortex pinning is due to normal point-like pinning centers. The temperature dependence of the critical current density suggests that the pinning due to the variation in the charge carrier mean free path alone is not sufficient to explain the experimental data. The magnetic relaxation rate as a function of temperature and magnetic field is also studied.