PT-195 SPIN DYNAMICS AND KNIGHT-SHIFT IN SINGLE-CRYSTALS OF UPT3

Pt-195 nuclear-magnetic-resonance measurements were performed on align ed single-crystal whiskers of UPt3 for temperatures from 4 to 50 K. A special alignment technique allows us to produce samples with very goo d c-axis alignment and to work with the field parallel to the c axis w ith an excellent signal-to-noise ratio. Combining the Knight shift and spin-lattice-relaxation data, we show a continuous cross-over from pa ramagnetic behavior above 40 K toward a degenerate-Fermi-liquid behavi or below 5 K. Antiferromagnetic spin fluctuations appear to be respons ible for this crossover process, and dominate all low-frequency magnet ic properties of this compound. The anisotropy ratios of both the spin -lattice and the spin-spin relaxation rates are found to be temperatur e independent. Analyzing these ratios we find that the imaginary part of the dynamic spin susceptibility is slightly stronger in the basal p lane.