Crystal structure, magnetism, and superconductivity ofYBa2(Cu1−xFex)3O7+ywithx=0.05–0.15

Abstract

Neutron scattering experiments and magnetic-susceptibility measurements have been performed to investigate the structural and magnetic properties of ${\mathrm{YBa}}_{2}$(${\mathrm{Cu}}_{1\mathrm{\ensuremath{-}}\mathit{x}}$${\mathrm{Fe}}_{\mathit{x}}$${)}_{3}$${\mathrm{O}}_{7+\mathit{y}}$ with x=0.05, 0.10 (superconductors), and 0.15 (nonsuperconductor). Rietveld refinements of neutron diffraction at room temperature indicate that the Fe atoms occupy both the Cu(1) ``chain'' and Cu(2) ``plane'' sites---the occupation of the Cu(2) sites is about 30% of the total Fe content. Neutron-diffraction measurements down to 5.5 K indicate no evidence of long-range magnetic order; however, neutron small-angle scattering as a function of temperature shows a cusplike anomaly around 20 K. This suggests that the Fe-doped ${\mathrm{YBa}}_{2}$${\mathrm{Cu}}_{3}$${\mathrm{O}}_{7}$ system undergoes spin-glass ordering at low temperatures; accordingly, in the superconducting samples superconductivity and spin-glass coexist. Magnetic susceptibility for the nonsuperconducting sample gives further evidence for the spin-glass order. The results obtained are discussed in connection with the superconducting properties of this system.