  In the present investigation, we report a systematic study of Ag admixing in
MgB2 prepared by solid-state reaction at ambient pressure. All the samples in
the present investigation have been subjected to structural/ microstructural
characterization employing x-rays diffraction (XRD) and transmission electron
microscopic (TEM) techniques. The magnetization measurements were performed by
physical property measurement system (PPMS). 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) compatible with
coherence length of MgB2 (~5-6 nm). In order to study the flux pinning effect
of Ag admixing in MgB2, 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 5K. This corresponds to 9.23x10^7
A/cm^2 in self-field,5.82x10^7 A/cm^2 at 1T,4.24 x10^6 A/cm^2 at 3.6T and
1.52x10^5 A/cm^2 at 5T. However, intragrain Jc values for MgB2 sample without
Ag admixing are 2.59x10^6 A/cm^2,1.09x10^6A/cm^2,4.53x10^4 A/cm^2 and
2.91x10^3A/cm^2 at 5 K in self field, 1T, 3.6T and 5T respectively.. The high
value of intragrain Jc for Ag admixed MgB2 superconductor has been attributed
to the inclusion of MgAg nanoparticles into the crystal matrix of MgB2, which
are capable of providing effective flux pinning centres. A feasible correlation
between microstructural features and superconducting properties has been put
forward.
