Chemical control of hole-doped superconductivity and magnetism in Gd_2−xCe_xRuSr₂Cu₂O_10-δ

Three Gd_2−xCe_xRuSr₂Cu₂O_10-δ samples (x = 0.5, as prepared and after high pressure oxygenation and x = 0.7) have been investigated by synchrotron powder x-ray diffraction and magnetization measurements. Precise coordinates and site occupancies for the oxygen atoms have been refined from the x-ray experiments. Estimates of the hole doping of the copper oxide planes based on the bond lengths, via the bond valence sum method, are found to be inaccurate. However, doping estimates based on the refined oxygen contents are in good agreement with the variation of superconductivity, and show that chemical doping, rather Cu/Ru band overlap, is the doping mechanism. The magnetic ordering temperatures of the Ru moments are not a simple function of the doping concentration, but depend upon both the Gd/Ce ratio and the oxygen content.