J_c-B performance study of an OCMG (Nd-Eu-Gd)-123 material doped by sub-micrometre Gd-211 particles

A concentration profile of Gd₂BaCuO₅ (Gd-211) fine particles embedded in an oxygen-controlled melt-grown (Nd_0.33Eu_0.33Gd_0.33)Ba₂Cu₃O_7-y (NEG-123) material is studied. The secondary phase had a nominal content of 30 mol% and was refined by the addition of 0.5 mol% Pt and 1 mol% CeO₂. The main concern of this paper is devoted to the variation of the magnetic properties and Gd-211 phase distribution in a bulk NEG-123 pellet of 1.8 cm in diameter and 1 cm in height. J_c(B) dependences deduced from magnetic hysteresis curves measured by SQUID were analyzed with respect to the appearance of the central and second peaks. A successful fit of all the curves by an analytical function composed of two additive contributions representing the central and second peaks is reported. The separation of these two contributions revealed that the shape of the high-field part of the magnetization curves is mostly governed by the pinning mechanism(s) responsible for the second peak and no `background' from another source of pinning is involved.