Influence of Ni, Fe, and Zn substitution on the superconducting and antiferromagnetic state of YBa2Cu3O7- delta.

TLDR: The concentration dependence of the Pauli susceptibility and the electrical conductivity indicates that the shift of the Fermi energy towards the mobility edge with increasing degree of substitution is one important mechanism for the suppression of the superconducting transition temperature.

Abstract: We report magnetic and electric measurements on $\mathrm{Y}{\mathrm{Ba}}_{2}{\mathrm{Cu}}_{3}{\mathrm{O}}_{7\ensuremath{-}\ensuremath{\delta}}$ with up to 15 at.% substitution of Ni, Fe, and Zn for Cu in the insulating state ($\ensuremath{\delta}\ensuremath{\simeq}1$) and the metallic state ($\ensuremath{\delta}\ensuremath{\simeq}0.1$). The concentration dependence of the Pauli susceptibility and the electrical conductivity indicates that the shift of the Fermi energy towards the mobility edge with increasing degree of substitution is one important mechanism for the suppression of the superconducting transition temperature. In the insulating antiferromagnetic state the Fe and Ni spins are very weakly coupled to the Cu spins. The Ni spins remain paramagnetic down to the lowest measuring temperature of 3 K, the Fe spins order at 5 K, independent of the Fe concentration. The N\'eel temperature depends weakly on the Fe and Zn concentration but decreases strongly with the Ni concentration. This different behavior reflects the different site preference for the substitution in the insulating state, namely Cu(2) for Ni and Cu(1) for Fe and Zn.