High-temperature post-annealing to improve J_c -B-T properties of MgB₂ thin film synthesized via hybrid deposition combining thermal evaporation of magnesium and sputtering of boron

Abstract

A new in situ process for depositing MgB2 film is being developed in the present study as a candidate method to facilitate the mass production of MgB2-thin-film superconducting tapes. Here, a MgB2 film was synthesized on a heated copper substrate via “hybrid deposition,” comprising thermal evaporation of magnesium and sputtering of boron. High-temperature post-annealing was performed to increase the critical current density (J c ) of the MgB2 thin films obtained via hybrid deposition. The J c of the MgB2 film deposited at 360 °C by hybrid deposition and post-annealed at 430 °C was drastically improved to 1100 A mm−2 at 20 K under 4 T, 79 000 A mm−2 at 15 K under 3 T, and 59 000 A mm−2 at 10 K under 5 T under a magnetic field parallel to the film. It was expected that the incorporation of hybrid deposition in processing using a reel-to-reel machine would facilitate the synthesis of high-J c , long MgB2-thin-film superconducting wires.