Unconventional Spin-Orbit Torques by 2D Multilayered MXenes for Future Nonvolatile Magnetic Memories.

MXenes have attracted attention in recent years owing to their 2D layered structures with various functionalities. To open a new application field for MXenes in the realm of electronic devices, such as ultrahigh-integrated magnetic memory, a spin-orbit torque (SOT) bilayer structure with MXene of CrN is developed: substrate//CrN/[Co/Pt]/MgO using the magnetron sputtering technique. Field-free current-induced magnetization switching in the bilayer structure is demonstrated, regardless of the charge current directions with respect to the mirror symmetry lines of CrN crystal. This is a specific characteristic for the 2D MXene-based SOT-devices. As the SOT efficiency increases with increasing the CrN thickness, the first-principles calculations predict an intrinsic orbital-Hall conductivity with the dominant out-of-plane component, comparing to the spin-Hall conductivity in the CrN. X-ray magnetic circular dichroism reveals the out-of-plane uncompensated magnetic moment of Cr ( ) in the CrN layer at the interface, induced by contact with the Co in the [Co/Pt] ferromagnetic layer. Therefore, the intrinsic bulk orbital-Hall effect in MXene and the interfacial contribution such as spin-filtering-like effect owing to are considered as possible major mechanisms for the unconventional out-of-plane SOT in the device, rather than a crystal symmetry and/or an interlayer exchange coupling.