Out-of-Plane Polarization from Spin Reflection Induces Field-Free Spin-Orbit Torque Switching in Structures with Canted NiO Interfacial Moments

TL;DR

This paper demonstrates field-free spin-orbit torque switching in a CoFeB/MgO system by leveraging out-of-plane spin polarization generated through spin reflection at a NiO interface with canted moments, eliminating the need for an external in-plane magnetic field.

Contribution

The study introduces a novel method of achieving field-free SOT switching using NiO interfacial moments to generate out-of-plane spin polarization, advancing spintronics technology.

Findings

Achieved near 100% switching ratio without external magnetic field.

Confirmed out-of-plane spin polarization contribution via hysteresis shift measurements.

Demonstrated thermal stability and reduced current shunting with NiO incorporation.

Abstract

Realizing deterministic current-induced spin-orbit torque (SOT) magnetization switching, especially in systems exhibiting perpendicular magnetic anisotropy (PMA), typically requires the application of a collinear in-plane field, posing a challenging problem. In this study, we successfully achieve field-free SOT switching in the CoFeB/MgO system. In a Ta/CoFeB/MgO/NiO/Ta structure, spin reflection at the NiO interface, characterized by noncollinear spin structures with canted magnetization, generates a spin current with an out-of-plane spin polarization {\sigma}z. We confirm the contribution of {\sigma}z to the field-free SOT switching through measurements of the shift effect in the out-of-plane magnetization hysteresis loops under different currents. The incorporation of NiO as an antiferromagnetic insulator, mitigates the current shunting effect and ensures excellent thermal stability of the device. The sample with 0.8 nm MgO and 2 nm NiO demonstrates an impressive optimal switching ratio approaching 100% without an in-plane field. This breakthrough in the CoFeB/MgO system promises significant applications in spintronics, advancing us closer to realizing innovative technologies.