Characterization of pinning in (Y, Nd)Ba₂Cu₃O _7-δ melt-textured superconductors

The pinning properties of (Y, Nd)Ba₂Cu₃O _7-δ [(Y, Nd)123] melt-textured samples have been studied using dc magnetic-based measurements and different scaling approaches over the temperature range 60 K ≤ T ≤ 84 K. The field dependence of the magnetically induced current density showed a peak effect with a shape which appeared to be sensitive to the morphology of the (Y, Nd)₂BaCuO _5-δ [(Y, Nd)211] inclusions, particularly at high temperatures >77K. Scaling of the normalized pinning force density (F_p/F _p,max) versus normalized applied field (h = B/B_irr) showed a clear indication that the dominant pinning mechanism is caused by spatial variations of critical temperature (T_c), [δ(T _c)-pinning effect], due to spatial fluctuations in the matrix composition. The increased concentration of Nd and the increased number of rare earth elements (RE) involved in the (123) structure appeared to significantly shift the scaled field position (h₀) corresponding to the maximum scaled pinning force density, highlighting the importance of RE/Ba and RE/ RE exchanges for the δK(T_c)-pinning effect. In the low field region, the scaling was not perfect due to an additional pinning effect caused by 211 inclusions. Scaling using peak effect coordinates implied a close relationship to a small bundle pinning regime.