  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.
