A defect detection method for MgB_2 superconducting and iron-based Ba(Fe,Co)_2As_2 wires

摘要

In this article, a method allowing for the detection of damage in iron-based superconducting bulks and MgB_2 wires is presented. MgB_2 wires were made of in situ material with ex situ MgB_2 barrier. The iron superconductor studied was Ba(Fe,Co)_2As_2. This material was surrounded by Nb barrier and placed inside an iron tube. All samples were annealed in the isostatic pressure of 1 GPa. Transport measurements were made using a four-contact probe. The transition of Nb and ex situ MgB_2 barrier from superconducting into resistive state (first transition) was observed at a temperature range from 5 K to 10 K and can be attributed to damage in either the Nb or ex situ MgB_2 barrier in these samples. For samples with a damaged barrier, it was not possible to determine the critical current density of the wires. The analysis indicates that annealing at 1 GPa leads to the Ba(Fe,Co)_2As_2 material with critical temperatures of 27 K and 21.5 K at upper critical flux density (B_(c2))of 14 T.