89Y NMR of the spin-chain system Ca2Y2Cu5O10

We report measurements of the Y-89 NMR lineshape, spin-lattice relaxation time T-1, and spin-spin relaxation time T-2 for the copper-oxide spin-chain compound Ca2Y2Cu5O10. The NMR data presented here, obtained at 17 MHz (8.1 T), show broad, asymmetric, two-peaked lineshapes with width Delta nu approximate to 90 kHz. The appreciable shift of the line, Delta H/H approximate to 0.7%, decreases with increasing temperature. T-2 increases with increasing temperature at lower temperatures, but plateaus at T-2 = 13 +/- 1 ms for temperatures above 325 K. For the spin-lattice relaxation, we observe a T-1 minimum around 275 K that is 100 times more shallow than expected for random Y-89-Cu2+ dipolar interactions. Such behavior indicates unusually strong spin correlations, and is surprising for the apparently small intrachain exchange coupling, J(nn)/k(B) approximate to 40 K. The long Cu2+ electronic timescale (tau(e) similar to 10(-8) s) evident at temperatures below the T-1 minimum indicates a slowing down of spin correlations far above T-N.