Anomalous behavior of nickel-gallium substitutions in YBa 2Cu 3O 7−δ

Abstract

Substitution of Ni and Ga together for Cu in YBa 2Cu 3O 7−δ is found to produce markedly different changes in superconducting transition temperatures than would be expected from the individual dopants. These elements were selected for their physical similarity to copper, so that any anomalous behavior might be interpreted as due primarily to the differing valences and the nickel magnetic moment. Substitutions of Zn and Ga were also studied, and the smaller deviation from the individual dopant behavior suggests that the magnetic nature of Ni may be significant perturbation to the high-temperature superconducting state. These results are consistent with a transition temperature decrease from the Ni magnetic moment competing with an increase from the NiCu valence difference.