2000, Hinzke, Denise, Nowak, Ulrich, Usadel, Klaus-Dieter

We investigate the thermally activated magnetization switching in a classical Heisenberg spin chain driven by an external magnetic field. For small system sizes we expect that the magnetic moments rotate coherently, while in the case of larger system sizes the magnetization reversal is proposed to be due to soliton-antisoliton nucleation. We compare Monte Carlo simulations with the direct integration of the Landau-Lifshitz-Gilbert equation of motion with Langevin dynamics as well as with asymptotic solutions for the escape rates following from the Fokker-Planck equation, finding agreement for low temperatures and high damping. We also discuss deviations in the intermediate temperature regime.

2000, Acharyya, Muktish, Nowak, Ulrich, Usadel, Klaus-Dieter

2000, Roters, Lars, Hucht, Alfred, Lübeck, Sven, Nowak, Ulrich, Usadel, Klaus-Dieter

We analyze interface motion in the random field Ising model with quenched disorder by means of Monte Carlo simulations. In the absence of thermal fluctuations a depinning transition occurs at some critical threshold field. We study the interface motion in the vicinity of the threshold field by varying the temperature as well as the driving field. It turns out that thermal fluctuations yield a rounded transition which can be characterized by a critical exponent.