Comparison of paramagnetic- and nonmagnetic-impurity effects on superconductivity in Nd1.85Ce0.15CuO4

Abstract

The effects of substitution of Co, Ni, or Zn for Cu in the electron-doped superconductors, Nd1.85Ce0.15Cu1−xMxO4 (with M=Co, Ni, or Zn, x≤0.05), have been investigated by powder x-ray diffraction analysis and resistivity, magnetic-susceptibility, and Hall-coefficient measurements. It is observed that only 0.7% Co or 0.8% Ni substitution for Cu destroys superconductivity. On the contrary, for the Zn-substituted samples, it is observed that Tc decreases proportionally to x and the magnitude of Tc is ∼9 K even for the 2% Zn-substituted sample. This result suggests that the pair-breaking effect plays a dominant role in the suppression of superconductivity in the Co- or Ni-substitute samples. The absolute values of the exchange-interaction energy between an electron and a Co ion and of that between an electron and a Ni ion are estimated at ∼0.09 and ∼0.08 eV, respectively. These values are comparable to those of the conventional BCS-type superconductors containing paramagnetic impurities. Both the absolute value of the Hall coefficient (‖RH‖) and its temperature coefficient (d‖RH‖/dT) are found to decrease as x increases for all the samples at temperatures higher than 120 K. However, for the Co-substituted samples, it is clearly observed that ‖RH‖ increases proportionally to x at 30 K, while ‖RH‖ decreases monotonically with increasing x for the Ni- or Zn-substitute samples. Therefore, it seems that there are no clear relations between the temperature dependence of RH and the suppression in the magnitude of Tc due to the substitutional effects.

Source-reported materials — not catalogue approval

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