We prepared MgB2 thin films using an electron-beam evaporation technique. TEM observation of the detailed microstructure for the films with and without substrate-spin during deposition revealed that the MgB2 columnar grains align in the direction of B flux. Jc of the film is higher in perpendicular fields than in parallel fields, whereas Bc2 and Birr have the opposite anisotropy. A detailed study on the relationship between the Jc anisotropy and the texture geometry of MgB2 columnar grains revealed that Jc becomes maximal where the magnetic field direction aligns in the direction of the MgB2 columnar-grain boundaries. The results indicate conclusively that the columnar-grain boundaries in MgB2 act as effective pinning centers.
