Superconducting properties of nanocrystalline MgB2 thin films made by an in situ annealing process

We have studied the structural and superconducting properties of MgB2 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 MgB2 with very small grain sizes. A zero-resistance transition temperature (Tc0) of 34 K and a zero-field critical current density (Jc) of 1.3×106 A/cm2 were obtained. The irreversibility field was ∼8 T at low temperatures, although severe pinning instability was observed. The result is a step towards making the in situ deposition process a viable technique for MgB2 Josephson junction technologies.