Superconducting MgB2 films via precursor postprocessing approach

Superconducting ${\mathrm{MgB}}_2$ films with ${\mathrm{T}}_c\text{=38.6\hspace{0.17em}}\mathrm{K}$ were prepared using a precursor-deposition, ex situ postprocessing approach. Precursor films of boron, ∼0.5 μm thick, were deposited onto ${\mathrm{Al}}_2{\mathrm{O}}_3$ (102) substrates by electron-beam evaporation; a postanneal at 890 °C in the presence of bulk ${\mathrm{MgB}}_2$ and Mg metal produced highly crystalline ${\mathrm{MgB}}_2$ films. X-ray diffraction indicated that the films exhibit some degree of c-axis alignment, but are randomly oriented in plane. Transport current measurements of the superconducting properties show high values of the critical current density and yield an irreversibility line that exceeds that determined by magnetic measurements on bulk polycrystalline materials.