The effect of rare-earth substitution at the Ba site on the flux pinning properties of Y(Ba 2− xR x)Cu 3O 7− δ (for R=La, Pr, and Nd)

Abstract

The behavior of the critical current density ( J c) and critical temperature ( T c) with rare-earth substitution at the Ba site in Y(Ba 2− x R x )Cu 3O 7− δ (0⩽ x⩽0.15) (for R=La, Pr, and Nd) has been investigated. In the case of magnetic rare-earth substitutions (Pr and Nd), a specific secondary peak appears and grows in the J c– H curves with increasing x, whereas no such peak emerges in a case of nonmagnetic rare-earth (La) substitution. This result suggests that the magnetic moment at the Ba site is an important factor generating defects that act as effective “field-induced type” pinning centers. However, the magnetic moment does not directly affect the variation in T c. That is, while the T c of Pr-substituted samples decreases monotonically with increasing x, the T c of Nd-substituted samples exhibits a maximum at low x (∼0.05), as is the case for La-substituted samples. Accordingly, Nd substitution is considered to be the most effective way of enhancing J c, because of its ability to generate defects that can act as effective pinning centers without inducing any noticeable suppression of superconductivity in the matrix.