Asymmetric magnetization reversal in dipolarly coupled spin valve structures with perpendicular magnetic anisotropy

Magnetization reversal has been studied in a Co₇₄Tb₂₆/Cu/Co₈₈Tb₁₂ system, which is a perpendicularly magnetized ferrimagnetic bilayer separated by a nonmagnetic layer. The Co₈₈Tb₁₂ (soft) layer (SL) exhibits a switching field much lower than the Co₇₄Tb₂₆ (hard) layer (HL), which enabled us to study the magnetization reversal of the SL for different magnetic states of the HL. We found an asymmetric hysteresis loop for the SL, when the HL is not fully saturated. Using careful analysis of magnetic force microscopy measurements we conclude that the asymmetry originates from magnetic domains formed in the HL that affect the SL reversal. A simple model based on magnetic dipolar interaction between the two layers is found to be in good agreement with the experimental data.