Interaction of Magnetization Centers of Different Signs as the Cause of the Nonmonotonic Field Dependence of the Domain Wall Velocity in Synthetic Pt/Co/Ir/Co/Pt Ferrimagnets

Abstract

The purpose of the work is to find the dependence of growth rate of magnetization centers of various types on their surrounding by other nucleation centers in a synthetic Pt/Co/Ir/Co/Pt ferrimagnet with perpendicular magnetic anisotropy. The following four types of nucleation centers exist in a sample with two ferromagnetic layers of different thicknesses: P⁺ centers correspond to the regions where the magnetizations of the thick and thin Co layers are directed along an applied field (↑↑); P^– centers are the regions where the magnetizations of the layers are opposite to an applied field (↓↓); and AP⁺ and AP^– centers correspond to the regions where the magnetizations of the thick and thin Co layers are opposite to each other and the total magnetic moment is along (↑↓) or opposite to (↓↑) an applied field, respectively. P^– nucleation centers are found to be surrounded by AP⁺ regions in any field and exhibit a monotonic field dependence of their boundary. The field dependence of the growth rate of AP^– nucleation centers is nonmonotonic since, as the field increases, they are surrounded by AP⁺ nucleation centers, AP⁺ and P^– regions, and only P^– nucleation centers in strong fields.