Critical magnetic field for lifting the degeneracy of monochiral domain walls with strong interlayer antiferromagnetic coupling

The addition of spatial inversion asymmetry and significant spin-orbit coupling to synthetic antiferromagnets (SAFs) has led to a lot of fundamental discoveries and technological applications. Here, we experimentally demonstrate that the critical magnetic field for breaking the degeneracy of monochiral domain walls (DWs) to realize the spin-orbit torque (SOT)-induced magnetization switching can be varied in a wide range from field free to $3000\phantom{\rule{4pt}{0ex}}\mathrm{Oe}$ in perpendicularly magnetized CoPt/Ru/CoPt SAFs with strong interlayer antiferromagnetic coupling, which strongly depends on the interfacial Dzyaloshinsky-Moriya interaction (DMI) and SOT at the bottom and top interfaces with multiple inversion asymmetries. Our DW dynamical calculations further reveal that the field-free magnetization switching is caused by SOT-induced left-handed chiral N\'eel DW displacement under the condition that the interfacial DMI of the upper magnetic layer has a significantly smaller value than that of the lower magnetic layer. These findings provide key insights for understanding the role of SOT and DMI in magnetization switching of magnetically coupled chiral systems and pave the way to practical applications of SAFs.