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In this work, MgB2 (with C-coated boron powders) wires were fabricated using the Internal Magnesium Diffusion (IMD) method. To improve flux pinning within the superconducting matrix under applied magnetic fields up to 12 T, the central magnesium rods were coated with different metallic layers, namely Cu, Sn, and Ag, as low-temperature activators. The low-temperature activation effect of Cu coating in IMD-processed MgB2 wires has been previously demonstrated in our earlier work [1]. In the first stage, 200 nm Cu-, Sn-, and Ag-coated MgB2 wires were comparatively investigated to evaluate the effects of metallic activator coatings on MgB2 phase formation and superconducting performance. Subsequently, the effect of Cu coating thickness was further examined by preparing Cu-coated Mg rods with coating thicknesses of 200, 400, 600, and 800 nm, aiming to promote MgB2 formation at lower sintering temperatures and shorter reaction times. In addition, we have found that C-doping of 4% was effective for higher Jc values at low fileds below 7T, while 10% C coating on Boron was very effective in transport Jc measurements at 10 T. Regardless of the origin of Polaron and phonons for the pair mechanism, we will present the effects various dopants for Jc, and Tc performances of the manufactured wires.
The thermal behavior and associated microstructural evolution of the processed Cu-, Sn-, and Ag-coated MgB2 wires were investigated using Differential Thermal Analysis (DTA) and Scanning Electron Microscopy (SEM). Resistance–temperature (R–T) measurements were performed under various applied magnetic fields, and the corresponding superconducting transition behavior, upper critical field (Hc2), and irreversibility field (Hirr) were analyzed. The transport Jc results showed that the highest value among the mono-core wires was obtained for the 200 nm Cu-coated MgB2 wire, reaching 3.9 × 10⁴ A/cm² at 4.2 K and 10 T. Finally, based on the optimized Cu activator approach, 7-filament MgB2 wires were fabricated using 200 nm Cu-coated Mg rods, and a Jc value of 1.2 × 10⁵ A/cm² was achieved at 4.2 K and 10 T.