Superconducting properties of nanocrystalline MgB${}_2$ thin films made by an in situ annealing process

Abstract

We have studied the structural and superconducting properties of MgB${}_2$ thin films made by pulsed laser deposition followed by in situ annealing. The cross-sectional transmission electron microscopy reveals a nanocrystalline mixture of textured MgO and MgB${}_2$ with very small grain sizes. A zero-resistance transition temperature ($T_{c0}$) of 34 K and a zero-field critical current density ($J_c$) of $1.3\times 10^6$ A/cm${}^2$ were obtained. The irreversibility field was $\sim$ 8 T at low temperatures, although severe pinning instability was observed. These bulk-like superconducting properties show that the in situ deposition process can be a viable candidate for MgB${}_2$ Josephson junction technologies.