Magneto-optical study of Ba(Fe$_{1-x}$T$_{x}$)$_2$As$_2$ (T=Co, Ni) single crystals irradiated with heavy-ions

TL;DR

This study demonstrates that heavy-ion irradiation can significantly enhance the critical current densities in Ba(Fe$_{1-x}$T$_x$)$_2$As$_2$ superconductors, with effects varying based on compound, temperature, and magnetic field.

Contribution

It provides new insights into how heavy-ion irradiation improves current-carrying capacity in pnictide superconductors, highlighting dose-dependent effects and compound-specific responses.

Findings

Enhanced critical current densities observed after irradiation.

Magneto-optical imaging revealed increased Bean penetration fields.

Irradiation effects depend on compound, temperature, and magnetic field.

Abstract

Optimally doped single crystals of Ba(Fe$_{1-x}$T$_x$)$_2$As$_2$ (T=Co, Ni) were irradiated with 1.4 GeV $^{208}$Pb$^{56+}$ ions at fluences corresponding to matching fields of $B_{\phi}=0.1, 0.5, 1$ and 2 T. Magneto-optical imaging has been used to map the distribution of the magnetic induction in the irradiated samples. The imaging is complemented by the magnetization measurements. The results show a substantial enhancement of the apparent critical current densities as revealed by the much larger Bean penetration fields and an increase of the hysteretic magnetization. However, the effect depends on the compound, temperature and applied magnetic field. In \FeCo crystals, at 15 K and low fields, the enhancement appears to scale with the irradiation dose at a rate of about 0.27 MA$\cdot$cm$^{-2}$T$^{-1}$, whereas in \FeNi crystals, higher irradiation doses are less effective. Our results suggest that moderate irradiation with heavy ions is a an effective way to \emph{homogeneously} enhance the current-currying capabilities of pnictide superconductors.