Comparative study of in situ and ex situ MgB2 films prepared by pulsed laser deposition

Two types of MgB2 film were prepared by pulsed laser deposition with in situ and ex situ annealing processes, respectively. Significant differences in properties between the two types of films were examined. The ex situ annealed MgB2 film has a Tc of 38.1 K, while the in situ film has a suppressed Tc of 34.5 K. The resistivity at 40 K for the in situ film is larger than that of the ex situ film by a factor of 6. The residual resistivity ratios are 1.1 and 2.1 for the in situ and ex situ films, respectively. A large slope of the Hc2-T curve was achieved in the in situ annealed film. The Jc-H curves of the in situ film show a much weaker field dependence than those of the ex situ film, attributable to stronger flux pinning in the in situ film. The small-grain (<100 nm) feature and high oxygen level detected in the in situ annealed MgB2 film may be decisive for the significant improvement of Jc and Hc2