SPIN DYNAMICS IN CUO AND IN LA2CUO4 UNDER CHARGE AND SPIN SUBSTITUTIONS FROM NQR NMR RELAXATION

NQR-NMR relaxation measurements in Cu1-xLixO and La2-xSrxCuO4 (for x<0 .05) are presented. The effects of the charge defects on the spin dyna mics of the parent AF compounds are first addressed, discussing how fl uctuations in the Cu2+ spin configuration are induced by the diffusion -like motion of the extra holes and deriving quantitative information on the correlation time and on the energy gap between localized and mo bile states. The similarities and the differences between CuO:Li and L a2CuO4:Sr are emphasized. The correspondent situation arising upon spi n substitution in La2Cu1-yZnyO4 and in La2Cu1-yNiyO4 is then briefly p resented.