Enhancement in Superconducting Properties of MgB₂ Prepared by Mechanical Milling

Abstract

The influence of mechanical milling of the corresponding powder elements on the formation of superconducting MgB₂ phase was investigated. Ma and B powders were attrition-milled, and then the milled power mixture was annealed under atmospheric pressure of argon. It was observed that amorphous B powders were embedded in Mg powders by the milling process. The composite layers of B and Mg had a thickness of ca. 1μm on the surface of Mg powders. After relatively low temperature annealing, superconducting MgB₂ phase formed from the composite surface layers. MgB₂ phase clearly appeared after annealing the 60 min milled powder mixture at 500℃. The results indicate that the Mg and B composite surface layers may be microscopically mixed, and may have a highly disordered crystal structure, which would provide a strong driving force for the formation of MgB₂ at lower temperature than can be achieved conventionally. In addition, it became apparent that the 60 min milled mixture led to much larger diamagnetism magnitude at 4 K than that was milled for 5 min. From the above results, it is clear that the mechanical milling of the powder elements can enhance the reactivity for the formation of MgB₂.