Hysteretic magnetization in micron-thick YBa2Cu3O7-delta films in nearly parallel magnetic fields

In an attempt to characterize hysteresis losses in micron-thick and c-axis- oriented YBa2Cu3O7-delta films, we studied their magnetization behavior in moderately low magnetic fields (H less than or equal to 0.1 T) oriented nea r the nb plane (0 degrees less than or equal to theta less than or equal to 10 degrees, theta is the angle between the ab plane and the applied field) . It is demonstrated that for the field oriented very close to the ab plane (0 degrees less than or equal to theta less than or equal to 2 degrees), t he magnetization is dominated by its component along the nb plane (M-ab) Th e angular dependence of magnetization M(theta) followed the equation M(thet a) = M-ab cos theta + M-c, sin 8, where M, is the magnetization due to the screening currents in the nb plane. M, was estimated by (1) the transverse magnetization that is equal to M-c for small theta values, and by (2) measu ring magnetization with field applied along the c axis. However, in some sa mples, the former and M(theta) were less than the latter. We attribute it t o flux penetration along the ab plane. The penetrating flux can induce weak links at the grain boundaries thereby causing the screening currents to fl ow in smaller loops.