Comparative Study of Dense Bulk MgB$_2$ Materials Prepared by Different Methods

TL;DR

This study compares dense MgB$_2$ bulk materials prepared by hot deformation, high pressure sintering, and mechanical alloying, revealing improved superconducting properties in the latter methods and identifying anisotropy in hot deformed samples.

Contribution

It provides a comparative analysis of different preparation methods for MgB$_2$ and their effects on superconducting properties, highlighting the advantages of high pressure sintering and mechanical alloying.

Findings

High upper critical fields ($rac{1}{2}23$ T) in sintered and alloyed samples

Enhanced irreversibility fields ($rac{1}{2}0.8H_{c2}$) in improved samples

Critical current density of $10^5$ A/cm$^2$ at 20 K and 1 T in selected samples

Abstract

We report on the results of a comparative investigation of highly dense bulk MgB$_2$ samples prepared by three methods: (i) hot deformation; (ii) high pressure sintering; and (iii) mechanical alloying of Mg and B powders with subsequent hot compaction. All types of samples were studied by ac-susceptibility, dc-magnetization and resistivity measurements in magnetic fields up to $\mu_0H=160$ kOe. A small but distinct anisotropy of the upper critical field $H_{c2}^{a,b}/H_{c2}^{c}\sim1.2$ connected with some texture of MgB$_2$ grains was found for the hot deformed samples. The samples prepared by high pressure sintering as well as by mechanical alloying show improved superconducting properties, including high upper critical fields $H_{c2}$ ($\mu_0H_{c2}(0)\sim23$ T), irreversibility fields $H_{irr}$ which are strongly shifted towards higher values $H_{irr}(T)\sim0.8H_{c2}(T)$ and high critical current $J_c$ ($J_c=10^5$ A/cm$^2$ at 20 K and 1 T).