Microwave absorption study of pinning regimes in $\bf Ba(Fe_{1-x}Co_x)_2As_2$ single crystals

TL;DR

This study investigates vortex pinning effects in Ba(Fe_{1-x}Co_x)_2As_2 superconductors using microwave absorption measurements across different doping levels, revealing how pinning mechanisms vary with doping and temperature.

Contribution

It provides a detailed analysis of how different pinning regimes dominate in underdoped, optimally doped, and overdoped Ba(Fe_{1-x}Co_x)_2As_2 superconductors, based on microwave absorption data.

Findings

Underdoped crystals exhibit extbackslash dtc-pinning due to magnetic order.

Optimally and overdoped samples show pinning governed by structural imperfections.

Pinning mechanisms depend on doping level and temperature.

Abstract

Magnetic field dependent modulated microwave absorption (MMWA) measurements have been carried out to investigate vortex pinning effects in single crystals of the iron-based high-Tc superconductor Ba(Fe_{1-x}Co_x)_2As_2 with three different cobalt doping levels of x = 0.07, 0.09, and 0.11. The dependence of the MMWA hysteresis loops on temperature, magnetic field, and Co-concentration have been measured and analyzed using a theoretical model of microwave absorption in superconductors. The analysis reveals that in an underdoped crystal (x = 0.07) the so called \dtc-pinning due to magnetically ordered regions defines the temperature dependence of the critical current density, while in the optimally doped (x = 0.09) and overdoped (x = 0.11) samples the pinning is governed by structural imperfections due to inhomogeneous distribution of cobalt dopant and has the so called \delta-l character.