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Magnetic relaxation in a classical spin chain

2000; American Physical Society; Volume: 61; Issue: 10 Linguagem: Inglês

10.1103/physrevb.61.6734

1095-3795

D. Hinzke, U. Nowak,

Advanced Thermodynamics and Statistical Mechanics

With decreasing particle size, different mechanisms dominate the thermally activated magnetization reversal in ferromagnetic particles. We investigate some of these mechanisms for the case of a classical Heisenberg spin chain driven by an external magnetic field. For sufficiently small system size the magnetic moments rotate coherently. With increasing size a crossover to a reversal due to soliton-antisoliton nucleation sets in. For even larger systems many of these soliton-antisoliton pairs nucleate at the same time. These effects give rise to a complex size dependence of the energy barriers and characteristic time scales of the relaxation. We study these quantities using Monte Carlo simulations as well as a direct integration of the Landau-Lifshitz-Gilbert equation of motion with Langevin dynamics and we compare our results with asymptotic solutions for the escape rate following from the Fokker-Planck equation. Also, we investigate the crossover from coherent rotation to soliton-antisoliton nucleation and multidroplet nucleation, especially its dependence on the system size, the external field, and the anisotropy of the system.