Angular dependence of magnetic relaxation and remanent magnetization on YBCO/PBCO superlattice and YBCO thin film

We measured the angular dependence of magnetic relaxation and remanent magnetization at various temperatures on a YBCO/PBCO superlattice and a YBCO thin film to investigate the fluctuation of the anisotropy of flux pinning. The measuring temperatures were from 20 K to T-c,T-onset and the applied magnetic field was 1000 Oe. The angles between the applied magnetic field and the c-axis of superlattices were 0 degrees, 30 degrees, 45 degrees, 60 degrees,.... In the measurement of the angular dependence of remanent magnetization, the angles between the magnetometer and c-axis were from -90 degrees to 90 degrees. The Anderson-Kim model was introduced to derive the pinning potential. It was observed that only the component of applied magnetic field along c-axis of the samples contributed to flux pinning and we also obtained the relation, M(theta) = M(parallel to) cos theta, where M(parallel to) is the magnetization along the c-axis. The causes are discussed.