INTRINSIC PARAMAGNETIC CENTERS IN 1-2-3-SUPERCONDUCTORS

The Tm-169 ''enhanced'' NMR in TmBa2Cu3O6+x (x = 0.5, 0.6) at temperatures below 4.2 K and the (CU)-C-63(1) NQR in YBa2Cu3O6.5 at temperatures above 4.2K are used to study properties of intrinsic paramagnetic centers incorporated into superconducting materials. The spin-lattice relaxation of thulium and copper nuclei reveals three types of paramagnetic centers to be present in oxygen-deficient 1-2-3 superconductors, those are (1) two-level ones with a spin S = 1/2, localized outside CuO2 bilayers, (2) singlet-ground-state paramagnetic centers with an integer spin S greater than or equal to 1 in CuO2 bilayers, and (3) exchange copper-oxygen clusters with a half-integer spin S greater than or equal to 5/2, localized in a nearest neighborhood of CuOx basal plane at boundaries of superconducting OrthoII microdomains.