LI-7 NUCLEAR-MAGNETIC-RESONANCE SPECTRA AND RELAXATION IN NI1-XLIXO

Li-7 nuclear magnetic resonance (NMR) spectra and relaxation rates in Ni1-xLixO, for 0.01 less than or equal to x less than or equal to 0.46 and for 20 less than or equal to T less than or equal to 550 K are pr esented. For x less than or equal to 0.2 the antiferromagnetic (AF) ph ase typical of NiO is still observed. The Neel temperatures T-N(x), th e temperature dependence of the field at the Li site, and the role of the extra holes in driving the correlated spin dynamics of Ni2+ are de rived. In particular, from Li-7 relaxation rates W the hopping frequen cies of the holes on the AF background and the energy gaps between iti nerant and localized states are extracted. In the mixed regime (x grea ter than or equal to 0.3, LiNiO2 structure-type) in which partial orde ring on alternate Li+ and Ni3+ layers occurs, Li-7 NMR data display th e features typical of disordered paramagnets, consistent with a pictur e of random distribution of Ni3+ (S=1/2), Ni2+ (S=1) and of spin vacan cies Li+ (S=0). In particular, for x=0.46, on cooling, paramagnetic-li ke divergence of the width and of the shift of the NMR line is observe d while Li-7 W's indicate slowing down of the spin fluctuations. The f luctuation frequency decreases in the MHz range below a freezing tempe rature T-f similar or equal to 40 K. (C) 1996 American Institute of Ph ysics.