Perpendicular exchange coupling in ferrimagnetic bilayers: An atomistic simulation modelling

Highlights: • Atomistic modelling of the Interfacial coupling between the soft/hard ferrimagnetic bilayers. • Tunable coercive field, exchange bias, and different switching time by engineering the strength of the exchange coupling. Understanding spin dynamics in perpendicular exchange coupled ferrimagnetic materials is an issue of crucial importance for progress in information processing and recording technology. In this paper, the Landau-Lifshitz-Gilbert equation at atomistic-level is employed to model the perpendicular interfacial exchange effect in ferrimagnetic FeGd/FeTb soft/hard bilayer structures. Three types of magnetization switching features are identified by tuning the interfacial exchange strength to be weak coupling, partial coupling, and strong coupling. These features have been further verified by the dynamical simulations, showing the switched soft layer could also help the hard layer magnetization switching. Based on the coercivity difference of the soft layer and hard layer, the left- or right-shift perpendicular exchange bias effect has been theoretically modelled.