Nonequilibrium Dynamical Phase Transition of a Three-Dimensional Kinetic Heisenberg Spin System

We systematically investigate the dynamical response of a three-dimensional kinetic isotropic Heisenberg spin system (HSS) to an external driving field by Monte Carlo numerical simulation. The dynamical response of isotropic HSS differs obviously from those of the anisotropic Ising spin system in which no real stable ordered state and relevant dynamical phase transition were observed in the kinetic HSS. There is a threshold time after which the magnetization m(t) in the HSS driven by a symmetrical external field always tends asymptotically to a disorder state regardless of the initial state of the system. The threshold time depends on the reduced temperature T/T_C of the investigated spin system, amplitude H₀ and frequency of the external field, i.e., τ = C.ω^α.H^-β₀.(T/T_C)^-γ. C is a constant equal to 0.0302 for a three-dimensional lattice and exponents α = 1.18±0.01, β = 1.81±0.01 and γ = 1.68±0.01.