Normal state exchange couplings in high-TC superconductors doped with Gd as revealed by ESR

Measuring the electron spin resonance of Gd3+ - spies doped in Y Ba2 Cu3 O7-δ oriented powders we have studied the spin-spin interactions between the conduction electrons and localized spins. The data give evidence for an exchange coupling of these paramagnetic ions to the doped charge carriers. By analyzing the spin dynamics in terms of the metal theory the corresponding exchange integrals were evaluated. We discuss the different contributions to the exchange interaction and a comparison with similar results obtained for intermetallic superconducting materials is given. (authors)