Interfacial spin-orbitronic effects controlled by different oxidation levels at the Co / Al interface

Perpendicular magnetic anisotropy (PMA) and Dzyaloshinskii-Moriya interactions are key interactions in modern spintronics. These interactions are thought to be dominated by the oxidation of the Co/Al interface in the archetypal platinum-cobalt-aluminum oxide system. However, in this study, we observe a double sign change in the anisotropy and about threefold variation in interfacial chiral interaction, influenced not only by the oxidation, but also by the metallic Al thickness. Contrary to previous assumptions about negligible spin-orbit effects at light metal interfaces, we observe not only strong PMA with fully oxidized Al, decreasing and turning negative (in-plane) with less oxygen at the Co/Al interface, but also that the magnetic anisotropy reverts to positive (out-of-plane) values at a fully metallic Co/Al interface. These findings suggest modification in the Co d band via Co/Al orbital hybridization, an effect supported by x-ray absorption spectroscopy and ab initio theory calculations, highlighting the key impact of strain on interfacial mechanisms at a fully metallic Co/Al interface.