SPIN DYNAMICS IN SR14CU24O41 FROM CU-63 NQR-NMR AND SUSCEPTIBILITY MEASUREMENTS

Cu-63 NMR-NQR relaxation measurements in oriented powders of Sr14Cu24O 41, in the temperature range 4.2 K less than or equal to T less than o r equal to 600 K and for magnetic-field intensities up to 9.4 T, are p resented. This compound has a complex structure comprising alternating layers containing Cu(1)O-2 chains and Cu(2)(2)O-3 two-leg ladders. At high temperatures Cu-63(2) nuclear relaxation rates probe the Cu(2)(2 +) spin dynamics in the two-leg ladders and an overall agreement with the theoretical predictions for the temperature and field dependence o f T-1 and T-2G is observed. In particular, 1/T-1 proportional to ln(1/ omega(e)+/-omega(R)), With omega(e) the electron Larmor frequency and omega(R) the nuclear resonance frequency. At low temperatures (T less than or equal to 150 K), an extra contribution to Cu-63(2) NMR-NQR rel axation rates is observed and tentatively related to the Cu(1)(2+) cor related spin dynamics. In this temperature range the magnetic field is observed to cause an anomalous reduction of 1/T-1, 1/T-2G, and of the de susceptibility. The analysis of the temperature dependence of the Cu-63(2) NQR frequency evidences a stabilization in the local lattice distortions below similar or equal to 85 K, where also Cu(1)(2+) spin dimerization is observed. The relevance of these distortions in drivin g the Cu(1)(2+) spin dimerization is thus discussed.