PROPERTIES OF UPPER CRITICAL-FIELD AND PINNING POTENTIAL IN EPITAXIALGDBA2CU3O7-DELTA THIN-FILM

We have measured the resistive transition of epitaxial GdBa2Cu3O7-delt a thin film in magnetic field up to 7.5T. The angular dependence of up per critical field, H, measured at a constant field of 7.5T exhibits a behaviour of H(theta)proportional to sin theta, showing that only t he component of magnetic field perpendicular to CuO2 plane gives rise to the dissipation related to Lorentz force. The field dependence of a ctivated energy U for the flux motion follows a logarithmic dependence , U-0 proportional to lnH, a typical 2D behavior. The 2D behavior exhi bited in GdBa2Cu3O7-delta epitaxial thin film is argued that the magne tic moment of Gd3+ ion suppresses the coupling of CuO2 planes.