Microscopic Structure and Flux Pinning Effect in the Sm_xBa_1-xCuO_y System

Abstract

The substitution for the Ba sites in Sm_1/3Ba_2/3CuO_y (=SmBa₂Cu₃O_y) by Sm induces the local oxygen disordering in the Cul-O planes since the Sm atoms located on the Ba sites are apt to have eight oxygen coordination. In order to investigate the effectiveness of the disordered oxygens as pinning centers for flux lines in Sm_xBa_1-xCuO_y, the magnetic hysteresis curves were examined by SQUID magnetometer. As a result, the critical current density J_c, which is estimated from the magnetic hysteresis curves, decreased with increase of degree of the oxygen disordering in the Cul-O planes of SmxBa_1-xCuO_y. Thus, the disordered oxygens do not act as effective pinning centers. This result is in contrast to the result in YBa₂(Cu_1-xFex)₃O_y system where the J_c has the maximum value at about x=0.02, and indicates that the increase of Jc in the YBa₂(Cu_1-xFe_x)₃O_y system is ascribed not to the disordering oxygens, but to the clustered Fe atoms.