Vortex phase diagram of Ba(Fe0.93Co0.07)2As2 single crystals

TL;DR

This study investigates the vortex behavior in Ba(Fe$_{0.93}$Co$_{0.07}$)$_{2}$As$_{2}$ single crystals, revealing similarities to cuprate superconductors, including a fishtail magnetization effect and insights into vortex pinning and creep mechanisms.

Contribution

It provides detailed electromagnetic measurements and analysis of vortex dynamics in this Fe-based superconductor, highlighting its similarities to high-$T_c$ cuprates and elucidating pinning regimes.

Findings

Observation of fishtail magnetization in $M(H,T)$ loops.

Supercurrent density estimated at approximately 2.6×10^5 A/cm$^2$ at 5 K.

Identification of a crossover from collective to plastic creep regimes.

Abstract

Detailed measurements of the global and local electromagnetic properties of Ba(Fe$_{0.93}$Co$_{0.07}$)$_{2}$As$_{2}$ single crystals are reported. Analysis of the irreversible magnetic response provides strong evidence for similar vortex physics in this Fe-based pnictide superconductor to the high-$T_{c}$ cuprates, such as Y-Ba-Cu-O or Nd-Ce-Cu-O. In particular, we have found a nonmonotonic "fishtail" magnetization in $M(H,T=const)$ loops and its signature is also present in $M(H=const,T)$ scans. The supercurrent density is evaluated by using several techniques, including direct transport measurements. At 5 K we estimate its value to be a moderate $j \approx 2.6 \pm 0.2 \times 10^5$ A/cm$^2$. Analysis of the magnetic relaxation is consistent with the collective pinning and creep models (weak pinning and fast creep) and suggests a crossover from the collective to the plastic creep regime in fields exceeding the value corresponding to the maximum in fishtail magnetization.