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Time-dependent spin-autocorrelation functions at T = ∞ for classical Heisenberg magnets in dimensionalities d = 1, 2., and 3 are investigated by means of a computer simulation. These functions are shown to exhibit power-law long-time tails of form t-ad with characteristic exponents αd which differ significantly from the values αd(SD) = d/2 predicted by the phenomenological spin-diffusion theory: α1 = 0.609 ± 0.005, α2 = 1.050 ± 0.025, α3≃1.6. The method to employ computer simulations for this problem differs from methods previously employed. Anomalous spin diffusion is confirmed by existing proton spin-lattice relaxation data for the quasi-1D s = 5/2 Heisenberg antiferromagnet (CH3)4 NMnCl3.

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© 1988 The American Physical Society