Special properties of overdoped 123 compounds; Cu(2) NQR and Tm NMR of TmBa2Cu30x at low temperatures

摘要

The 169Tm NMR and 63Cu(2) NQR spectra, as well as the spin-spin and spin-lattice relaxation of thulium nuclei, are studied in a series of oriented TmBa2Cu30( powders with an oxygen content x from 6.9 to 7.0 (in Ax=0.02 intervals). All the experiments are performed by the spin-echo technique at liquid helium temperatures. Additional measurements of the diamagnetic susceptibility at 1 kHz in a field H_1-1 Oe perpendicular to the c crystallographic axis show that the maximum critical temperature 7"c(onset)=92.2 K is achieved in the samples with j:=6.90-6.92. The results of the experiments with the overdoped compounds (j:^6.94) are consistent with the "ribbon model" of the quasi-one-dimensional spin and charge correlations in CuO2 planes [O. N. Bakharev, M. V. Eremin, and M. A. Teplov, JETP Lett. 61,515 (1995)]. A "disappearance" of 1/3 of the intensity of the Cu(2) NQR signal is discovered when the oxygen content is decreased from 7.00 to 6.98. Phase separation is discussed as a possible cause of this effect. It is theorized that in layers with a reduced concentration of holes in the CuO2 planes, the mobility of the holes decreases, the fluctuations of the strong internal fields from the spins of the Cu2+ ions slow, and the spin echo of the Cu(2) nuclei is not observed due to acceleration of the transverse nuclear relaxation.