Magnetic and magneto-optic characterization of the ternary compounds (Nd_0.33Eu_0.33Gd_0.33)Ba₂Cu₃ O_y,(Sm_0.33Eu_0.33Gd_0.33)Ba₂CU ₃O_y and (Nd_0.33Sm_0.33Gd_0.33) Ba₂Cu₃O_y

We have investigated the ternary compound superconductors (Nd_0.33Eu_0.33Gd_0.33)Ba₂Cu ₃O_y (NEG), (Sm_0.33Eu_0.33Gd_0.33)Ba₂Cu ₃O_y (SEG) and (Nd_0.33Sm_0.33Gd_0.33)Ba₂Cu ₃O_y (NSG) melt-processed in a reduced oxygen atmosphere with magnetic and magneto-optical measurements. Zero-field-cooled and field-cooled measurements were carried out in order to correlate the flux distributions with microstructure analysis. It was found that the critical state is well established in all three samples. The J_c(B) curves derived from magnetization loops exhibit a strongly developed secondary peak effect. Scaling of normalized J_c as a function of reduced field, b = B/B_pk, was performed. At 77 K and above, it was found that NSG and SEG samples have similar properties, which are different from those of the NEG sample. The current-carrying length scale was determined from the reverse leg of the magnetization hysteresis loops and was compared with the actual dimensions of the sample.