Angular dependence of the irreversible magnetization of Y Ba2 Cu3 O7 superconducting thin films

Y${\mathrm{Ba}}_{2}$${\mathrm{Cu}}_{3}$${\mathrm{O}}_{7}$ superconducting thin films have been studied by magnetization measurements in oblique fields up to 0.8 T both at low temperature and at temperatures close to ${T}_{c}$. Both components of magnetization parallel and perpendicular to the applied field could be measured with two pairs of crossed detection coils. In all cases the magnetization is found to be perpendicular to the film plane. This is due to the self-field effects related to the thin-film geometry which force the critical currents to circulate along the film plane. At low temperature the properties are found to depend only on the component of the applied magnetic field perpendicular to this plane, as expected in the situation where demagnetizing field effects are dominant. However, at temperatures close to ${T}_{c}$ the critical currents and therefore the pinning are found to increase when the applied field approaches the film plane. This is attributed to the effect of intrinsic pinning which may be related to the kink structure of the vortices in oblique fields.