Anisotropic enhancement of flux pinning in mixed rare earth 123-type thin films

By transport measurements, we demonstrate that critical current density and irreversibility field are improved in the mixed rare earth NEG123 films for both field directions of H/spl par/c and H/spl perp/c. Angular dependence of the enhanced flux pinning force at low temperature and field is characterized by two peaks at H/spl par/c and H/spl perp/c, respectively. This may be attributed to favorite distribution of stress fields in such two directions due to 2D lattice misfits. With increasing temperature and field, the strongest improvement of flux pinning take places only at the field perpendicular to the (a, b) plane where intrinsic flux pinning is absent, thus allowing the stress field, such an uncorrelated disorder, to be most effective by collective pinning behavior.