141Pr and 169 Tm NMR study of superconducting PrCeCuO and TmBaCuO

Abstract

The NMR spectra and nuclear relaxation of 141Pr3+ and 169Tm3+ ions in oriented powders of high-Tc superconductors Pr1.85Ce0.15CuO4-y (Tc=24K) and TmBa2Cu3O7-y (c=91K) at temperatures well below Tc were investigated. The relaxation of Pr nuclear transverse magnetization at temperatures down to 0.05K gives an evidence for the trivalent state of Ce ions in the superconducting phase of the PrCeCuO compound. Two types of Tm centers inTmBaCuO were observed (of orthombic and tetragonal symmetry), exhibiting similar parameters of NMR spectra, but completely different relaxation rates. Anomalously slow nuclear transverse relaxation of tetragonal Tm centers at liquid helium temperatures allows one to conclude that those centers are formed by single Tm ions and/or small clusters. © 1991.