Investigation of Gd Addition Added on Magnetic and Structural Properties of Bi_(1.8)Pb_(0.35)Sr_(1.9)Ca_(2.1)Cu_3Gd_xO_y Superconductors by ac Susceptibility

摘要

This study reports the effect of Gd addition on magnetic and structural properties of Bi_(1.8)Pb_(0.35)Sr_(1.9)Ca_(2.1)Cu_3Gd_xO_y superconductor with x = 0, 0.1, 0.2, 0.3, 0.4 and 0.5 by means of ac susceptibility measurements at various ac fields (ranging from 270 to 1352 A/m) and scanning electron microscopy (SEM) images. Critical onset ((T_c)~(on)) and loss peak temperatures (T_p) were qualitatively estimated from the ac susceptibility curves. The peak temperature at zero ac-magnetic field (T_(p0)) and intergrain critical current densities (T_C) were theoretically calculated from the ac susceptibility plots via the critical state models. The results show that peak temperatures and critical current densities were found to decrease with increasing Gd addition. Moreover, using a self-field approximation together with J_c dependence on temperature, the characteristic length (L_c) associated with the pinning force is estimated to be approximately the same as the average grain size (R_g) of the pinning center because of the linear decrease in J_c with increasing temperature. Surface morphology and grain connectivity of the samples were also obtained to degrade with increase in the Gd addition from SEM investigations.