Critical Currents at the Grain Boundary of Sm1Ba2Cu3O7−δ Film Under Oblique Magnetic Fields

We measured critical current densities (J_cb) at a [001]-tilt grain boundary (GB) of a bicrystalline Sm₁Ba₂Cu₃O₇ film under various magnetic fields (Halpha) applied obliquely. The mis-orientation angle, thetas, of the [001] tilt GB was 30deg. Halpha was varied between -0.65 KOe and +0.65 KOe. The angle, phi, between the applied fields and the film surface was varied from 0deg to 90deg. The curves of J_cb vs. H_alpha at the different phi s were qualitatively explained by a simple formula suggested in [8]. The formula was expressed by multiplication of the two factors which include the effects of Hperp and H_par. One fitting parameter, alpha, in this formula was large for the sample of thetas = 30deg in our previous paper. On the contrast, alpha for the present sample in this paper is almost zero. The absolute values of J_cb for this sample are larger than those for the previous sample by one order of magnitude. These results indicate that the parameter, alpha, closely related to the quality of GB: alpha gets smaller as the film quality at GB become better.