ANGULAR-DEPENDENCE OF THE IRREVERSIBLE MAGNETIZATION OF YBA2CU3O7 SUPERCONDUCTING THIN-FILMS

YB2Cu3O7 superconducting thin films have been studied by magnetization measurements in oblique fields up to 0.8 T both at low temperature an d a temperatures close to T-c. Both components of magnetization parall el and perpendicular to the applied field could be measured with two p airs of crossed detection coils. In all cases the magnetisation is fou nd to be perpendicular to the film plane. This is due to the self-fiel d effects related to the thin-film geometry which force the critical c urrents to circulate along the film plane. At low temperature the prop erties are found to depend only on the component of the applied magnet ic filed perpendicular to this plane, as expected in the situation whe re 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.