Correlation of magnetic and magneto-optical properties with microstructure analysis in melt-textured (Nd_0.33Sm_0.33Gd_0.33)Ba₂Cu₃O_y

Magnetic properties of the melt-processed ternary superconductor (Nd_0.33Sm_0.33Gd_0.33)Ba₂Cu₃O_y (`NSG') with non-homogeneously distributed NSG-211 particles were investigated by means of magnetic and magneto-optical measurements. Flux distributions obtained by means of magneto-optic imaging after zero field-cooling and field-cooling were analyzed in order to understand the flux penetration behavior of this compound. The current-carrying length-scale was determined from the reverse leg of the magnetization hysteresis loops and compared to the actual dimensions of the sample. This was done both on the whole sample and on three individual domains to which the sample was subsequently divided. Magnetization hysteresis loops of all samples exhibited a strongly developed secondary peak in the temperature range 30 K≤T≤77 K. The critical current and pinning force densities derived from these data were normalized to the values at the peak position, J_max and F_max, respectively, and analyzed as a function of applied field reduced both to the respective peak field and irreversibility field.