Extraordinary Hall effect and x-ray spectroscopy measurements have been performed on a series of Pt/Co/MOx trilayers (M=Al, Mg, Ta, etc.) in order to investigate the role of oxidation in the onset of perpendicular magnetic anisotropy at the Co/MOx interface. It is observed that varying the plasma oxidation time modifies the magnetic properties of the Co layer, inducing a magnetic anisotropy crossover from in plane to out of plane. We focused on the influence of plasma oxidation on Pt/Co/AlOx perpendicular magnetic anisotropy. The interfacial electronic structure is analyzed via x-ray photoelectron spectroscopy measurements. It is shown that the maximum of out-of-plane magnetic anisotropy corresponds to the appearance of a significant density of Co–O bondings at the Co/AlOx interface.

The influence of thermal annealing on Pt/Co/AlOx trilayers has been investigated up to 450°C as a function of the plasma oxidation time of the AlOx layer. Both magnetic properties of the Co layer and transport properties are strongly modified upon annealing. The perpendicular magnetic anisotropy reaches very large values, while the Hall angle increases with annealing temperature. This study reveals that this trilayer system possesses tunable magnetic anisotropy properties, which can be controlled by varying either oxidation time or annealing temperature. These results are compared with those obtained on standard Pt/Co/Pt trilayers which show, on the contrary, a continuous degradation of their magnetic properties upon annealing.