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, La 0.34 Na 0.66 Fe 2 As 2 , with, T c ≈ 27 K. 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 T c superconductors, evidencing a strong pinning behavior. The irreversibility line does not follow a power law behavior with (T c -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's critical-state model is found to be of the order of 10 5 A/cm 2 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 a 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 charge carrier mean free path alone is not sufficient to explain the experimental data. Magnetic relaxation rate as a function of temperature and magnetic field is also studied.

Vortex dynamics and second magnetization peak in the iron-pnictide superconductor Ca0.82La0.18Fe0.96Ni0.04As2

“…Figure 4 suggests that the mechanism responsible for the second magnetization peak appearing in M(H) curves in our sample is a crossover from collective to plastic pinning occurring as the SMP develops. It should be mentioned that such behavior, separating a low J c region from a higher J c region in U 0 vs. 1/J c isofield curves, has also been observed previously in systems which do not exhibit the second magnetization peak [11]. To further study this change in behavior, a more analysis of the activation energy was performed, as first presented in [45].…”

“…Vortex physics in iron-pnictide superconductors is of a great importance for many future technological advancements [1] as well as for the understanding of various exciting phases of vortex matter [2]. Among the various interesting phenomenon the crystal ab-plane [7] (and references therein), its occurrence has not been observed in some pnictide crystals even with H ∥ c-axis, as for instance in overdoped Ba-KFe 2 As 2 [8], in (Li-Fe)OHFeSe [9], in La-doped CaFe 2 As 2 [10] and in La 0.34 Na 0.66 Fe 2 As 2 [11]. The importance of the SMP appearing on isothermal magnetization curves relies on its direct association with the peak effect appearing in the magnetic field dependence of critical current density, J c (H) [12], which is of technological importance.…”

Second magnetization peak, anomalous field penetration, and Josephson vortices in KCa$$_2$$Fe$$_4$$As$$_4$$F$$_2$$ bilayer pnictide superconductor

“…This is due to more than one type of defect sites responsible for the vortex pinning in the sample. Such behavior has already been seen in other pnictide superconductors 44,81,82 . Since δl -type of pinning curve is closer to the experimental values, therefore δl -type pinning is likely to be the dominant one in the present case.…”

Vortex dynamics and second magnetization peak in the iron-pnictide superconductor Ca$_{0.82}$La$_{0.18}$Fe$_{0.96}$Ni$_{0.04}$As$_2$

“…Figure 4 that the mechanism responsible for the second magnetization peak appearing in M(H) curves in our sample is a crossover from collective to plastic pinning occurring as the SMP develops. It should be mentioned that such behavior, separating a low J c region from a higher J c region in U 0 vs. 1/J c isofield curves has also been observed previously in systems which do not exhibit the second magnetization peak [11]. To further study this change in behavior, a more rigorous analysis of the activation energy was performed, as first presented in Ref.…”

“…Such phenomenon is ubiquitous in various low-T c conventional [3,4] as well as in high-T c unconventional superconductors [5,6] and even in superconductors exhibiting multiple superconducting gaps, such as MgB 2 [4]. Also, the SMP has been investigated in nearly all families of iron-pnictide superconductors for magnetic field directions parallel and perpendicular to the crystal ab-plane [7] (and references therein), its occurrence has not been observed in some pnictide crystals even with H c-axis, as for instance in overdoped Ba-KFe 2 As 2 [8], in (Li-Fe)OHFeSe [9], in La-doped CaFe 2 As 2 [10] and in La 0.34 Na 0.66 Fe 2 As 2 [11]. The importance of the SMP appearing on isothermal magnetization curves relies on its direct association with the peak effect appearing in the magnetic field dependence of critical current density, J c (H) [12], which is of technological importance.…”