Micromagnetics simulation for magnetization switching of permalloy films with pure spin current injection

Pure spin current injection has recently been developed as an effective method of controlling magnetization in spintronic devices. In order to investigate the dynamics of the magnetization reversal process in magnetic films with pure spin current injection, we performed micromagnetics simulations based on the Landau-Lifshitz equation and taking into account a term representing spin transfer torque caused by the pure spin current. We studied the time evolution of magnetization in permalloy films and estimated the probability of magnetization switching to show how the probability depends on the width of the film and the intensity of the injected spin current. We found that, in narrow films, a transverse domain wall is formed in the film and that this wall moves outside the film when magnetization switching occurs. The switching time becomes shorter as the intensity of the injected spin current is increased. In wide films, on the other hand, magnetization switching does not occur even if the intensity of injected spin current is increased. In such cases, either a magnetic vortex core is formed or the configuration of the moments hardly changes from the initial magnetic state.