Perfect fits of J_c-B dependencies in NEG-123 bulk samples with 30% Gd-211 fine particles

Magnetization hysteresis loops (MHL) were measured on two NEG-123 bulk samples with addition of 30% Gd-211 fine (sub-micron) particles in the temperature range 65-88 K. These two samples possessed significantly different second-to-central peak heights ratios. Both sets of the J_c-B curves could be, however, fitted with a high precision by the same combined analytical function J_c(B) = J_cpexp(-αB/B_p) + J_spb_p exp[(1 - (B/B_p)ⁿ)/n] in all investigated temperatures. The pinning regimes governing formation of the central and second peak could be separated in this way. As far as the central peak contribution to the MHL becomes usually negligible at around B_p, the shape of J_c(B) above B_p is governed by only a high-field pinning mechanism. The central peak extends to this field region only at temperatures very close to T_c. Good scaling of the pinning force density with temperature gives a further support to the above conclusions.