Superconducting Properties and Microstructures of ${\rm MgB}_{2}$ Thin Films Fabricated With the Precursor and Post-Annealing Method

The critical current densities (
J

_c
) of MgB
₂
thin films deposited on alpha-Al
₂
O
₃
fabricated with a precursor and post-annealing process have been investigated in high magnetic fields of up to 30 T. The
H

_c2
(0) estimated from the resistivity measurements was ~45 T. High
J

_c
values were obtained at 4.2 K in external magnetic fields applied parallel to the film surface. These values were comparable to that of Nb
₃
Sn in fields up to 18 T and surpassed them in fields over 18 T. To reduce the number of droplets, the Eclipse PLD method was one of the most useful techniques.