Effects of unreacted Mg impurities on the transport properties of MgB2

TL;DR

This study investigates how unreacted magnesium impurities affect the electrical transport properties of MgB2 superconductors, revealing that impurities influence critical temperature, resistivity, and magnetoresistance.

Contribution

It demonstrates the impact of unreacted Mg impurities on MgB2's transport properties and provides insights into optimizing synthesis conditions for better superconducting performance.

Findings

Samples with less unreacted Mg had higher Tc and sharper transitions

Unreacted Mg caused increased resistivity and magnetoresistance

Presence of Mg impurities led to resistivity upturns at low temperatures

Abstract

We synthesized polycrystalline MgB2 from a stoichiometric mixture of Mg and the 11 B isotope under different conditions. All the samples showed bulk superconductivity with Tc = 38~39 K. The samples containing the least amount of unreacted Mg showed the highest Tc and the sharpest transition width (Delta_Tc). A residual resistivity ratio (RRR) of ~ 5.8, and a magnetoresistance (MR), at 40 K, of 12% were obtained for these samples. Moreover, there was no upturn of resistivity in a low temperature region at 10 Tesla. The samples containing appreciable amounts of unreacted Mg showed quite different behaviors; the values of Delta_Tc, RRR, and MR were much larger. An upturn appeared in resistivity of the samples below about 50 K at 10 T and is thought to be due to the unreacted Mg.