Stability and dynamics of synthetic antiferromagnetic skyrmions in asymmetric multilayers

Synthetic antiferromagnetic (SAF) multilayers offer a highly versatile platform for skyrmionic devices, providing skyrmions with exceptional mobility and a negligible skyrmion Hall effect (SkHE). However, detecting antiferromagnetic skyrmions is challenging due to their antiparallel spin alignment, and their behavior within asymmetrically parametrized ferromagnetic layers remains unclear. Here, we theoretically investigate the stability and transport properties of antiferromagnetically coupled skyrmions in multilayer systems comprising two ferromagnetic layers with distinct interfacial Dzyaloshinskii-Moriya interactions (DMIs). We show that coupled skyrmion pairs of opposite charge are stable over broad parameter ranges, even when the DMI vectors differ in both magnitude and sense. Our investigation into the transport properties reveals that the SkHE cancellation due to the topological neutrality of the skyrmion pair is robust against imbalances in several material parameters, including DMI and Gilbert damping, but is highly sensitive to imbalance in the current densities and saturation magnetizations. This suggests that synthetic ferrimagnets are generally ineffective in eliminating the SkHE. In contrast, we show that magnetically compensated SAF stacks with antiparallel DMI vectors not only eliminate the SkHE but also facilitate skyrmion detection.