Dynamic properties of a classical anisotropic Heisenberg chain under external magnetic field

We investigate the dynamic properties of a classical anisotropic Heisenberg chain interacting with an external magnetic field at different temperatures. Properties such as time-dependent energy autocorrelation and space-time spin-spin correlation are obtained by solving the dynamic equation S˙i=Si×∇SiH. While the static spin-spin correlation length decreases as the system is heated up, it increases when an external magnetic field is present. The time-dependent spin-spin correlation decreases when the system is heated up, resulting in a decrease of the spin-diffusion speed. The presence of the magnetic field contributes to the order, and therefore produces an increase of the spin-diffusion speed. In contrast, the single-ion type anisotropy behaves dynamically as a local field, inducing disorder in the chain.