Flux Pinning in Y_(1-x)M_(x)Ba_(2)Cu_(3)O_(7-δ)(M=Gd,Eu and Sm)System

In this paper,the flux pinning effects in Y_(1-x)M_(x)Ba_(2)Cu_(3)O_(7-δ)(M=Gd,Eu and Sm)samples are reported.It is found that there is another pinning mechanism under higher magnetic fields in addition to that under lower fields.This pinning effect may stem from the lattice stress field resulting from the partial substitution of the rare earth elements with different atomic radii for Y.