EVIDENCE FOR CROSSOVER EFFECTS IN THE SPIN DYNAMICS OF THE 2-DIMENSIONAL ANTIFERROMAGNET SR2CUO2CL2 FROM CL-35 NUCLEAR-MAGNETIC-RESONANCE

Cl-35 nuclear magnetic resonance (NMR) and relaxation measurements hav e been performed in stacked Sr2CuO2Cl2 single crystals with Neel tempe rature T-N = 257 K for two crystal orientations with respect to the ap plied field: H parallel to c and H perpendicular to c. All the paramet ers of Cl-35 NMR are found to exhibit a strong orientation dependence varying in temperature. In particular, the unconventional anisotropy a nd strong temperature dependence of the Cl-35 nuclear spin-spin relaxa tion rate, T-2(-1), are presented and discussed in terms of a crossove r of the Cu2+ spin dynamics from Heisenberg to XY-like correlation for T --> TNN+. The onset of anisotropic broadening and shift of the Cl-3 5 NMR line was observed well above T-N, which is in agreement with the previous results. (C) 1996 American Institute of Physics.