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

Abstract The NMR spectra and nuclear relaxation of 141 Pr 3+ and 169 Tm 3+ ions in oriented powders of high-T c superconductors Pr 1.85 Ce 0.15 CuO 4−y ( T c =24 K ) and TmBa 2 Cu 3 O 7−y ( c =91 K ) at temperatures well below T c 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.