Energy Transport in Magnetic Chains

Energy transport in magnetic chains with nearest-neighbor Heisenberg interactions is studied with emphasis on the high-temperature limit. Calculations are made of the energy diffusion constant $D_E$. The values obtained using standard approximations are compared with the results of a computer study of the dynamics of a chain of 2000 classical spins. It is found that the approximate values of $D_E$ are significantly smaller than the value obtained from the computer analysis. The discrepancy is shown to arise from the failure of the approximations to simulate the asymptotic behavior of the thermal-current correlation function. Energy diffusion in three-dimensional lattices is also discussed.