Increases in the Irreversibility Field and the Upper Critical Field of Bulk MgB2 by ZrB2 Addition

TL;DR

This study demonstrates that adding ZrB2 to bulk MgB2 significantly enhances its irreversibility and upper critical magnetic fields, improving superconducting properties up to 35 K.

Contribution

It is the first to show that ZrB2 addition increases critical fields and current density in MgB2, surpassing effects seen with SiC doping.

Findings

Bc2 increased from 20.5 T to 28.6 T

Birr increased from 16 T to 24 T

Critical current density improved across 4.2 K to 35 K

Abstract

In a study of the influence of ZrB2 additions on the irreversibility field, Birr and the upper critical field Bc2, bulk samples with 7.5 at. % ZrB2 additions were made by a powder milling and compaction technique. These samples were then heated to 700-900C for 0.5 hours. Resistive transitions were measured at 4.2 K and Birr and Bc2 values were determined. An increase in Bc2 from 20.5 T to 28.6 T and enhancement of Birr from 16 T to 24 T were observed in the ZrB2 doped sample as compared to the binary sample at 4.2 K. Critical field increases similar to those found with SiC doping were seen at 4.2 K. At higher temperatures, increases in Birr were also determined by M-H loop extrapolation and closure. Values of Birr which were enhanced with ZrB2 doping (as compared to the binary) were seen at temperatures up to 34 K, with Birr values larger than those for SiC doped samples at higher temperatures. The transition temperature, Tc, was then measured using DC susceptibility and a 2.5 K drop of the midpoint of Tc was observed. The critical current density was determined using magnetic measurements and was found to increase at all temperatures between 4.2 K and 35 K with ZrB2 doping.