Spin Diffusion in the S=1/2 Quasi One-Dimensional Antiferromagnet α-VO(PO₃)₂ via ³¹P NMR

Abstract

Low-frequency spin dynamics in the S=1/2 antiferromagnetic spin-chain compound α-VO(PO₃)₂ has been studied by means of ³¹P NMR. The nuclear spin-lattice relaxation rate 1/T₁ at the P site exhibits H^-1/2 dependence on the applied magnetic field (H) at temperatures (T) well above the intrachain coupling strength J/k_B = 3.50 K indicating one-dimensional diffusive spin dynamics. The diffusive contribution to 1/T₁ decreases on cooling as electronic spins acquire short-range antiferromagnetic correlations within the chain, and vanishes almost entirely around T ≈ 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 field-independent part of 1/T₁ increases with decreasing temperature, which may be a precursor for the true long-range antiferromagnetic ordering found below T_N = 1.93 ± 0.01 K.