Exchange spring structures and coercivity reduction in FePt∕FeRh bilayers: A comparison of multiscale and micromagnetic calculations

Abstract

Calculations of magnetization reversal mechanism and coercivity reduction in exchange coupled FePt∕FeRh bilayers are presented. It is shown by comparison with atomistic model calculations that the use of a standard micromagnetic model leads to an underestimation of the exchange energy at the interface, leading to a reduced coercivity decrease for small interfacial exchange energy constant. This is due to the failure of the domain wall (DW) to penetrate the hard FePt phase in the micromagnetic calculations. A multiscale model is proposed based an atomic level simulation in the interface region coupled with a micromagnetic approach elsewhere. This leads to improved calculations of DW structures at the interface, allowing a detailed study of the magnetization reversal mechanism. The new approach predicts a saturation in the coercivity reduction as a function of interface exchange energy at 4% of the bulk value, which is associated with complete continuity of the DW across the interface.