High critical current density and improved flux pinning in bulk MgB 2 synthesized by Ag addition

Abstract

In the present investigation, we report a systematic study of Ag admixing in Mg B2 prepared by solid-state reaction at ambient pressure. All the samples in the present investigation have been subjected to structural microstructural characterization employing x-ray diffraction and transmission electron microscopic (TEM) techniques. The magnetization measurements were performed by physical property measurement system. The TEM investigations reveal the formation of MgAg nanoparticles in Ag admixed samples. These nanoparticles may enhance critical current density due to their size (∼5-20 nm) which is compatible with the coherence length of Mg B2 (∼5-6 nm). In order to study the flux pinning effect of Ag admixing in Mg B2, the evaluation of intragrain critical current density (Jc) has been carried out through magnetic measurements on the fine powdered version of the as synthesized samples. The optimum result on intragrain Jc is obtained for 10 at. % Ag admixed sample at 5 K. This corresponds to ∼9.23× 107 A cm2 in self-field, ∼5.82× 107 A cm2 at 1 T, ∼4.24× 106 A cm2 at 3.6 T, and ∼1.52× 105 A cm2 at 5 T. However, intragrain Jc values for Mg B2 sample without Ag admixing are ∼2.59× 106, ∼1.09× 106, ∼4.53× 104, and 2.91× 103 A cm2 at 5 K in self-field, 1 T, 3.6 T, and 5 T, respectively. The high value of intragrain Jc for Ag admixed Mg B2 superconductor has been attributed to the inclusion of MgAg nanoparticles into the crystal matrix of Mg B2, which are capable of providing effective flux pinning centers. A feasible correlation between microstructural features and superconducting properties has been put forward. © 2007 American Institute of Physics.