Flux Pinning of the Stress Field in Y1-xLnxBa2Cu3O7-δ

Our experimental results of flux pinning effects in Y1- x Ln x Ba2Cu3O7-δ(Ln=Gd, Sm and Eu) samples show that for each partially substituted sample, there exists strong flux pinning at higher field in comparison with the undoped samples, and the maximum pinning force density F m a x p increases with the increasing of the atomic radius of Ln. Furthermore, the F m a x p (x) vs x curve is symmetrical with respect to x=0.5 in Y1- x Eu x Ba2Cu3O7-δ. It is suggested that there are two different flux pinning mechanisms in these samples. The pinning effect at higher field may stem from the lattice stress field due to the partial substitution of Ln with different atomic radii for Y. The pinning effect at lower field is caused by the magnetic interaction between a vortex and the grain surfaces.