HIGH-TEMPERATURE CU-63(2) NUCLEAR-QUADRUPOLE AND MAGNETIC-RESONANCE MEASUREMENTS OF YBA2CU4O8

We report data on the Gaussian transverse relaxation rate 1/T-2G, the Knight shift K-s, and the spin-lattice relaxation time T-1, in YBa2Cu4 O8 from 100 K up to 715 K, extending the upper temperature of previous studies by 200 K. The T-2G data are corrected for a small spin-lattic e fluctuation contribution to the echo decay. Calculations of T1T/T-2G and T1T/T-2G(2) show that there is a crossover in scaling behavior at a temperature T(cr)similar to 500 K; The Knight-shift data also exhib it a maximum at this temperature and decrease slowly with increasing t emperature above this. Calculations using an independent form for the susceptibility due to Sokol, Singh, and Elstner suggest that the corre lation length for antiferromagnetic fluctuations is on the order of on e: to two lattice spacings at this crossover temperature, in agreement with the proposal of Barzykin and Pines.