Significant enhancement of irreversibility field in clean-limit bulk MgB2

TL;DR

This study demonstrates that annealing clean-limit MgB2 bulk samples in Mg vapor significantly enhances their irreversibility and upper critical fields, making them more suitable for magnet applications, with minimal impact on critical temperature.

Contribution

It reveals a method to substantially increase the irreversibility field in MgB2 by annealing in Mg vapor, a novel approach for improving superconductor performance.

Findings

Hirr above 14 T at 4.2 K achieved

Resistivity increased from 1.0 to 18 microohm-cm

Tc decreased by only 1-2 K

Abstract

Low resistivity ("clean") MgB2 bulk samples annealed in Mg vapor show an increase in upper critical field Hc2(T) and irreversibility field Hirr(T) by a factor of 2 in both transport and magnetic measurements. The best sample displayed Hirr above 14 T at 4.2 K and 6 T at 20 K. These changes were accompanied by an increase of the 40 K resistivity from 1.0 to 18 microohm-cm and a lowering of the resistivity ratio from 15 to 3, while the critical temperature Tc decreased by only 1-2 K. These results point the way to make prepare MgB2 attractive for magnet applications.