SPIN DYNAMICS IN HOLE-DOPED S=1 2 CHAINS AND LADDERS FROM NMR AND SUSCEPTIBILITY MEASUREMENTS IN SR14-XNAXCU24O41/

The authors report on NMR-NQR, de susceptibility and resistivity measu rements in ST14-xNixCu24O41 for 0 less than or equal to x less than or equal to 2. The analysis of the de susceptibility points out that onl y a small fraction of Cu2+ spins are involved in the dimerization of C u(1)O-2 chains while the remaining spins possibly form Zhang-Rice sing lets with the localized holes. The role of structural distortions, evi denced either in NQR spectra or by anomalies in the resistivity measur ements, in assisting the dimerization is discussed. The introduction o f extra holes by Na+ doping is observed to slightly decrease the Cu(1) (2+) uniform static susceptibility at low temperatures, to reduce the amplitude of the gap between singlet and triplet states in the Cu(2)(2 )O-3 two-leg-ladders and to increase the conductivity. The amplitude o f the gap in the dimerized chain, derived either from de susceptibilit y or (23)Nal/T-1 was found to be the same, while a discrepancy is foun d in the estimate of the amplitude of the gap in the ladders by the sa me two techniques.