Critical currents at the grain boundary of (Sm0.8Dy0.2)Ba2Cu3O7 film under oblique magnetic fields

We measured critical current densities (Jcb) at the 30° grain boundary of a bicrystalline (Sm0.8Dy0.2)Ba2Cu3O7 film under various magnetic fields (H→a), which were applied obliquely. We varied the field from −0.7 kOe to +0.7 kOe while the angles (θ) of the fields were 2°, 22.5°, 45°, 67.5° and 90° with respect to the film surface. The curves of Jcb vs H→a showed the well known butterfly-like hysteretic curves. We separated the two components of field, H⊥ and H∥, which are normal and parallel to the film surface, respectively. Our data indicate that the roles of these two components for the field dependence of Jcb are different. We combined the effect of H⊥ deduced from the data for the normal field (θ = 90°) and the effect of H∥ deduced from the data for the almost parallel field (θ = 2°). Multiplying the independent reduction factors deduced from these two cases, we found a new formula, which expresses Jcb vs H→a for general θs. All the experimental data for various θs fit well to this new formula.