NATURE OF THE 4F SPIN IN HIGH-TC SUPERCONDUCTORS CONTAINING PARAMAGNETIC RARE-EARTH ELEMENTS GDBA2CU3O7-Y, DYBA2CU3O7-Y, HOBA2CU3O7-Y, ERBA2CU3O7-Y, TMBA2CU3O7-Y

Single-phase high T//c superconductors, REBa//2Cu//3O//7// minus //y (RE EQUVLNT Gd, Dy, Ho, Er and Tm) were prepared and their magnetic susceptibilities were measured from 77 to 300 K. The obtained Curie-Weiss temperatures were minus 1. 2, minus 5. 8, minus 2. 1 and minus 14 K for Dy**3** plus , Ho**3** plus , Er**3** plus and Tm**3** plus respectively, indicating that the 4f spins are delocalized to a small extent and the orbital quenching occurs in the normal conducting range. This was supported by the results of electron spin resonance (ESR) measurements. The influence of the magnetic spins on the superconductivity and the relaxation mechanisms responsible for the ESR lineshapes are discussed.