Influence of Ag nano-powder additions on the superconducting properties of Mg <TEX>$B_2$</TEX> materials

Silver nano-powder was added to Ma <TEX>$B_2$</TEX> to make (Ag)<TEX>$_{(x)wt.%}$</TEX>(Mg <TEX>$B_2$</TEX>)<TEX>$_{(l00-x)wt.%}$</TEX> (A <TEX>$g_{x}$</TEX>-Mg <TEX>$B_2$</TEX>) (10 <TEX>$leq$</TEX> x <TEX>$leq$</TEX> 50) composite superconductors to investigate the effect of the Ag nano-powder on the vortex pinning. Pellets made out of the mixed powder were put inside stainless steel tubes, which were sintered at 85<TEX>$0^{circ}C$</TEX> in Ar atmosphere. No impurity phase was identified for as-rolled samples. However, both the Mg <TEX>$B_2$</TEX> and the A <TEX>$g_{x}$</TEX>-Mg <TEX>$B_2$</TEX> composite pellets, when sintered, contain small amount of Mg <TEX>$B_4$</TEX> and MgAg impurity phases. From the magnetization study, it was found that the flux pinning was improved in the high magnetic field region (> 3 T) only when 10w/o Ag was added to Mg <TEX>$B_2$</TEX>. The "two step" structures in ZFC M(T) curve gradually increased as the amount of Ag added increased. Pinning centers can be created by adding a suitable amount of Ag nano-powder which is not too large to increase the decoupling between the Mg <TEX>$B_2$</TEX> grains.crease the decoupling between the Mg <TEX>$B_2$</TEX> grains.