Copper NQR and NMR study of metal-substituted yttrium barium(2) copper(3) oxygen(7) and yttrium barium(2) copper(4) oxygen(8)

Pulsed nuclear quadrupole resonance (NQR) and nuclear magnetic resonance (NMR) have been used to investigate the effect of metal-substitution for copper in {dollar}rm YBasb2Cusb3Osb7{dollar} (YBCO123) and {dollar}rm YBasb2Cusb4Osb8{dollar} (YBCO124). Among many metal substitutions, Zn has an especially dramatic effect in suppressing the superconducting temperature T{dollar}sb{lcub}c{rcub},{dollar} and hence superconductivity. More interesting is that Zn and Fe have the same T{dollar}sb{lcub}c{rcub}{dollar} suppression effect in YBCO124. This study focuses on the Zn substitutions in YBCO123 and Zn, Fe, and Co substitutions in YBCO124.; In Zn doped YBCO123, Cu(2), plane site, NQR spectra and the frequency dependence of the spin-lattice relaxation rates have been measured over a temperature range from 77 K to 300 K to study the correlation of the suppression of the relaxation rate with the distance between the probe Cu nuclei and the impurity. It is found that the relaxation rate is insensitive to the variation of the NQR resonance frequency. However, by comparing the results of the Zn doped YBCO124 with those of YBCO123, it can be concluded that the suppression of the relaxation rate for both YBCO compounds in the normal state is caused by destruction of short-range antiferromagnetic correlation with substitution of nonmagnetic ion Zn on the Cu(2) sites.; NQR and NMR measurements were carried out on both Cu(2), plane, and Cu(1), chain sites, for various concentrations of Zn, Fe, and Co dopants in YBCO124 over a temperature range from 77 K to 300 K. A strong correlation of the enhancement of Cu(2) spin lattice relaxation rate and suppression of superconductivity by impurities was found. The temperature dependence of the Cu(2) NMR linewidth exhibits a strong RKKY type exchange interaction below 225 K for Zn and Fe doped samples, which indicates the formation of the local magnetic moment. The enhancement of the relaxation rate is caused by the local magnetic moment Fe{dollar}sp{lcub}+3{rcub}{dollar} ion and the moments on Cu(2) neighbors when Zn{dollar}sp{lcub}+2{rcub}{dollar} is substituted on Cu(2).; This study gives us a clear picture of the spin pseudogap behavior in the high temperature superconductor cuprates. It also suggests that the magnetic moment on the CuO{dollar}sb2{dollar} plane may relate to the suppression of T{dollar}sb{lcub}c{rcub}{dollar} in metal-substituted YBCO124.