EFFECTS OF CHARGE DEFECTS ON THE CU2-DOPED CUO FROM NUCLEAR-RELAXATION( SPIN DYNAMICS IN LI+)

From a combination of NQR, NMR and AFNMR spectra in Cu1-xLixO informat ion on the electric and Magnetic electron-nucleus interactions is obta ined. In particular, it is argued that Li+ enters the CuO lattice up t o x congruent-to 4%, with a relatively small effect on the Neel temper ature T(N). Cu-63 NQR and AFNMR, and Li-7 NMR spin-lattice relaxation measurements are used to study the spin dynamics in the paramagnetic ( PA) and in the antiferromagnetic (AF) phase and the effects associated with the creation of holes upon lithium doping. The relaxation rates W indicate that the Cu2+ spin dynamics is almost unaffected by Li dopi ng for T >> T(N) and that it is possibly controlled by valence fluctua tions. Close to T(N) a crossover to an XY or to an Ising spin system d rives the transition to the ordered state. The Li doping modifies in a dramatic way the spin fluctuations in the AF phase, by increasing the relaxation rates by orders of magnitude and inducing temperature beha viour quite different from that in CuO. These effects are related to t he fluctuations in the local Cu2+ spin configuration due to the diffus ional motion of the extra holes in the electronic bands. A satisfactor y explanation of the temperature and frequency dependences of Li relax ation rates is given in terms of a correlation time tau(h) for the hol e motion controlled by an energy gap E(x) and quantitative information on tau(h) and E(x) are thus derived.