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

TL;DR

This study investigates vortex behavior and the second magnetization peak in Ca$_{0.82}$La$_{0.18}$Fe$_{0.96}$Ni$_{0.04}$As$_2$, revealing pinning mechanisms, vortex phase transitions, and high critical current densities relevant for applications.

Contribution

It provides detailed magnetic relaxation and isothermal magnetization analysis of the vortex state, highlighting vortex phase transitions and pinning mechanisms in this iron-pnictide superconductor.

Findings

Second magnetization peak observed for H // c-axis across all temperatures below Tc.

Pinning crossover from elastic to plastic near Hp, indicating a vortex phase transition.

High critical current density exceeding 10^5 A/cm^2, suggesting potential for technological applications.

Abstract

We report the studies of detailed magnetic relaxation and isothermal magnetization measurements in the vortex state of the 112-type iron-pnictide Ca$_{0.82}$La$_{0.18}$Fe$_{0.96}$Ni$_{0.04}$As$_2$ superconductor with $T_c$ $\sim$ 22 K. In the isothermal $M(H)$, a well defined second magnetization peak (SMP) feature is observed in the entire temperature range below $T_c$ for measurements with $H$ $\parallel$ $c$-axis. However, for $H$ $\parallel$ $ab$-planes, the SMP feature is suppressed at low temperatures, which might be due to 2D Josephson vortices forming at low temperatures and high magnetic fields in such an anisotropic system. A rigorous analysis considering the magnetic relaxation data for $H$ $\parallel$ $c$-axis suggests an elastic to plastic pinning crossover across $H_p$, which also seems accompanied with a possible phase transition in vortex lattice near $H_p$. Moreover, point disorder and surface defects are likely to be the dominant sources of pinning, which contribute to the $\delta l$-type of pinning in the sample. A high $J_c$, in access of 10$^5$ A/cm$^2$ observed could potentially make this material technologically important.