Flux-dynamics associated with the Second Magnetisation Peak in iron-pnictide Ba_{1-x}K_xFe_2As_2

TL;DR

This study investigates vortex dynamics in Ba_{1-x}K_xFe_2As_2 superconductors, revealing that the second magnetization peak is influenced by plastic vortex motion and collective pinning, with implications for understanding flux behavior.

Contribution

It provides detailed analysis of vortex regimes and pinning mechanisms associated with the second magnetization peak in iron-pnictide superconductors.

Findings

Irreversibility and peak position are time-dependent and governed by plastic vortex motion.

Vortex dynamics near the peak involve a transition from collective to plastic pinning.

Surface homogeneity ensures consistent superconducting properties across the sample.

Abstract

We report on isofield magnetic relaxation data on a single crystal of $Ba_{1-x}K_xFe_2As_2$ with superconducting transition temperature $T_c$= 32.7 K which exhibit the so called fish-tail effect. A surface map of the superconducting transition temperature shows that the superconducting properties are close to homogeneous across the sample. Magnetic relaxation data, M(t), was used to obtain the activation energy U(M) in order to study different vortex dynamics regimes. Results of this analysis along with time dependent measurements as a function of field and temperature extended to the reversible region of some M(H) curves demonstrate that the irreversibility as well the second magnetization peak position, $H_p(T)$, are time dependent and controlled by plastic motion of the vortex state. In the region delimited by a characteristic field Hon (well below $H_p$), and $H_p$, the vortex dynamics is controlled by collective pinning. For fields below Hon the activation energy, $U_0$, increases with field as expected for collective pinning, but the pinning mechanism is likely to be in the single vortex limit.