Inter- and Intra-granular Interactions of REBa₂Cu₃O_7−δ , RE: Eu, Gd, Ho and Er

Abstract

Here, the superconducting and AC/DC magnetic properties of REBa₂Cu₃O_7−δ (RE: Eu, Gd, Ho and Er) are investigated in order to understand the inter-granular and intra-granular behavior of these compounds. These compounds were prepared by standard solid-state reaction route. ErBa₂Cu₃O_7−δ (Er-123) and HoBa₂Cu₃O_7−δ (Ho-123) (consisting of heavier rare earth) show higher orthorhombic splitting in their XRD patterns than those observed for EuBa₂Cu₃O_7−δ (Eu-123) and GdBa₂Cu₃O_7−δ (Gd-123) (consisting of lighter rare earth). Even though Eu, Gd, Ho and Er are magnetic elements, substitution of these at Y site in Y-123 does not change the superconducting transition temperature (T _c). Er-123 and Ho-123 exhibit very sharp superconducting transition while Eu-123 and Gd-123 exhibit relatively broad transition with little hump at the lower part of transition close to the long-range superconducting state with zero resistance. In addition to that, Eu-123 and Gd-123 show relatively higher normal state resistivity than those of Er-123 and Ho-123. The AC susceptibility measurements reveal that these compounds possess different strength of inter-granular couplings. The hump in the superconducting transition of Eu and Gd is not due to the lack of inter-grain couplings in these samples because of having better grain connectivity in the samples as compared to other rare earth elements in REBa₂Cu₃O_7−δ system. Though intra-grain peak is insensitive to the applied magnetic field, inter-grain peak is sensitive to the applied magnetic field.