Field-free spin-orbit torque switching in a perpendicularly magnetized bilayer with a large interfacial saturation magnetization gradient

The deterministic spin-orbit torque (SOT) switching of a perpendicular magnetization requires the assistance of an external in-plane magnetic field to break in-plane inversion symmetry, which hinders the practical application of SOT devices. Here, we report on the large interfacial saturation magnetization gradient and field-free SOT switching in a perpendicularly magnetized Co2MnSi/D022-Mn3Ga bilayer. The high-quality sample grown by high-vacuum molecular-beam epitaxy not only exhibits nearly lattice-matching crystalline structure but also possesses large perpendicular magnetic anisotropy. The density functional theory calculations indicate a considerable magnetization gradient at the Co2MnSi/D022-Mn3Ga interface, which leads to a significant interlayer Dzyaloshinskii-Moriya interaction (DMI). Due to the symmetry breaking, efficient zero-field SOT switching has been realized in Hall-bar devices. The lateral shift of anomalous Hall loops under DC currents confirms a relatively high zero-field SOT efficiency chi SOT. Moreover, as revealed by the in-plane field Hx dependence of SOT switching behavior, the strength of DMI effective field Hg-DMI reaches up to 60 Oe. This work provides a promising strategy for realizing wafer-scale manufacture of all-electrically driven SOT devices.