Susceptibility, crystal-structure, and specific-heat studies of the high-Tc superconductor and quenched YBa2(Cu0.91Fe0.09)3Ox

Magnetic susceptibility, poweder x-ray diffraction, and specific-heat measurements were used to study the high-temperature superconductor YBa2(Cu0.91Fe0.09)3O7.1 and the nonsuperconductor quenched YBa2(Cu0.91Fe0.09)3O6.1 samples. The crystal structure for both samples is tetragonal with almost the same lattice parameters. No magnetic spin-glass state of Fe is observed in the two samples at low temperatures and the quenched sample exhibits antiferromagnetic behavior, whereas the magnetization is nonlinear as a function of the applied field. For the superconducting sample, magnetic irreversibilities appear below a temperature Tg whose field dependence differs substantially from that observed in spin glasses. Tg scales with the applied field as H14. The linear term obtained from the specific-heat studies is extremely high, =73 mJ/molK2.