Crystal structure, magnetism, and superconductivity of YBa2(Cu1−xFex)3O7+y with x=0.05–0.15

Abstract

Neutron scattering experiments and magnetic-susceptibility measurements have been performed to investigate the structural and magnetic properties of ${\mathrm{YBa}}_2$(${\mathrm{Cu}}_{1\mathrm{-}\mathit{x}}$ ${\mathrm{Fe}}_{\mathit{x}}$ ${)}_3$ ${\mathrm{O}}_{7+\mathit{y}}$ 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.