Spin diffusion in the S=1/2 quasi one-dimensional antiferromagnet alpha-VO(PO3)(2) via P-31 NMR

Low-frequency spill dynamics in the S = 1/2 antiferromagnetic spin-chain co mpound alpha -VO(PO3)(2) has been studied by means of P-31 NMR. The nuclear spill-lattice relaxation rate 1/T-1 at the P site exhibits H-1/2 dependenc e on the applied magnetic field (H) at temperatures (T) well above the intr achain coupling strength J/k(B) = 3.50 K indicating one-dimensional diffusi ve spin dynamics. The diffusive contribution to 1/T-1 decreases on cooling as electronic spins acquire short-range antiferromagnetic correlations with in the chain, and vanishes almost entirely around T approximate to J/k(B). This is accompanied by an apparent increase of the spin-diffusion constant from the value expected in the classical limit. On the other hand, the fiel d-independent part of 1/T-1 increases with decreasing temperature, which ma y be a precursor for the true long-range antiferromagnetic ordering found b elow T-N = 1.93 +/- 0.01 K.