Ni-substituted sites and the effect on Cu electron spin dynamics of YBa2Cu{3-x}NixO{7-\delta}

TL;DR

This study investigates how Ni substitution affects Cu electron spin dynamics in YBa2Cu3-xNixO7-δ using Cu nuclear quadrupole resonance, revealing site-specific impacts on superconducting transition temperature.

Contribution

It provides new insights into the site distribution of Ni and its role in suppressing superconductivity through nonmagnetic depairing effects.

Findings

Plane-site Ni(2) density is higher in quenched samples.

Quenched samples show faster Cu(2) relaxation, indicating more Ni(2).

Suppression of Tc linked to nonmagnetic effects of Ni(2).

Abstract

We report Cu nuclear quadrupole resonance experiment on magnetic impurity Ni-substituted YBa$_2$Cu$_{3-x}$Ni$_x$O$_{7-\delta}$. The distribution of Ni-substituted sites and its effect on the Cu electron spin dynamics are investigated. Two samples with the same Ni concentration $x$=0.10 and nearly the same oxygen content but different $T_c$'s were prepared: One is an as-synthesized sample (7-$\delta$=6.93) in air ($T_c$$\approx 80 K$), and the other is a quenched one (7-$\delta$=6.92) in a reduced oxygen atmosphere ($T_c$$\approx 70 K$). The plane-site $^{63}$Cu(2) nuclear spin-lattice relaxation for the quenched sample was faster than that for the as-synthesized sample, in contrast to the $^{63}$Cu(1) relaxation that was faster for the as-synthesized sample. This indicates that the density of plane-site Ni(2) is higher in the quenched sample, contrary to the chain-site Ni(1) density which is lower in the quenched sample. From the analysis in terms of the Ni-induced nuclear spin-lattice relaxation, we suggest that the primary origin of suppression of $T_c$ is associated with nonmagnetic depairing effect of the plane-site Ni(2).