Enhancement of the critical current density of MgB 2 thick films by Ag- and Cu-impurity layers

Abstract

We report on Ag and Cu doping in MgB 2 thick films using amorphous Ag- and Cu-impurity layers with various thicknesses, 4, 8, 16, and 32 nm. Firstly, Ag- and Cu-impurity layers were deposited on Al 2O 3(0 0 0 1) substrates at room temperature by using pulsed laser deposition system. Subsequently MgB 2 films were grown on the top of Ag or Cu/Al 2O 3 substrates at 560 and 600 °C by using hybrid physical–chemical vapor deposition. The effect of Ag and Cu doping as well as growth temperature on the microstructure and critical current density ( J c) of MgB 2 films were investigated. It was found that both of Ag/Cu doping and low growth temperature can significantly enhance J c without suppression of T c. The increase in J c results from improved grain connectivity and strong flux pinning by high density of grain boundaries and other types of defects introduced by Ag- or Cu-impurity layers.