2005 年 40 巻 11 号 p. 473-478
As-grown MgB2 thin films were prepared by an electron-beam evaporation method. In order to enhance the critical current density Jc in magnetic fields, the MgB2 thin film was deposited in an O2 atmosphere. E-J characteristics were measured in magnetic fields that were applied in various directions to investigate O2 doping effect and the angular dependence of pinning properties. The values of Jc and the glass-liquid transition temperature Tg of the O2-doped sample were larger than those of the non-doped sample and had peaks in the magnetic field applied parallel to the c-axis. It was found that c-axis correlated pinning centers were introduced by the deposition of the MgB2 thin film in an O2 atmosphere. The distributions of the local critical current density Jcl were derived by fitting obtained E-J characteristics with the theoretical expression based on the percolation transition model. As a result, it was found that the distribution of Jcl of the O2-doped sample became broad and shifted to the high current density region as compared to that of the non-doped sample. This is because pinning centers with strong pinning force were introduced by the deposition in the O2 atmosphere.