Keeseong Park

89Y NMR of the Spin‐Chain System Ca2Y2Cu5O10

We report measurements of the 89Y NMR lineshape, spin‐lattice relaxation time T1, and spin‐spin relaxation time T2 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 Δν ≈ 90 kHz. The appreciable shift of the line, ΔH/H ≈ 0.7%, decreases with increasing temperature. T2 increases with increasing temperature at lower temperatures, but plateaus at T2 = 13 ± 1 ms for temperatures above 325 K. For the spin‐lattice relaxation, we observe a T1 minimum around 275 K that is 100 times more shallow than expected for random 89Y−Cu2+ dipolar interactions. Such behavior indicates unusually strong spin correlations, and is surprising for the apparently small intrachain exchange coupling, Jnn/kB ≈ 40 K. The long Cu2+ electronic timescale (τe ∼ 10 −8 s) evident at temperatures below the T1 minimum indicates a slowing down of spin correlations far above TN.