  Oxidation strongly influences the properties of magnetic layers employed in
spintronic devices. We study the effect of oxidation on the structural,
magnetic, and electrical properties as well as current-induced spin-orbit
torques (SOTs) in Pt/Co/AlOx, Pt/CoOx/Co/AlOx, and PtOx/Co/AlOx layers. We show
how the saturation magnetization, perpendicular magnetic anisotropy, anomalous
Hall resistance, and SOT are systematically affected by the degree of oxidation
of both the Pt/Co and Co/Al interfaces. Oxidation of the Co/Al interface
results in a 21% and 42% variation of the dampinglike and fieldlike SOT
efficiencies, which peak at 0.14 and 0.07, respectively. The insertion of a
paramagnetic CoOx layer between Pt and Co maintains a very strong perpendicular
magnetic anisotropy and improves the dampinglike and fieldlike SOT
efficiencies, up to 0.26 and 0.20, respectively. In contrast with recent
reports, we do not find that the oxidation of Pt leads to a significant
enhancement of the torques. Rather, we find that oxygen migrates from Pt to the
Co and Al layers, leading to a time-dependent oxidation profile and an
effective spin Hall conductivity that decreases with increasing oxygen
concentration. Finally, we study current-induced switching in Pt/Co/AlOx with
different degrees of oxidation and find a linear relationship between the
critical switching current and the effective magnetic anisotropy controlled by
the oxidation of Al. These results highlight the importance of interfaces and
oxidation effects on the SOT and magnetotransport properties of heavy
metal/ferromagnet/oxide trilayers and provide information on how to improve the
SOT efficiency and magnetization-switching characteristics of these systems.

Applied Physics;Materials Science