Investigation of Metallic/Oxide Interfaces in Pt/Co/AlO $_{\rm x}$ Trilayers by Hard X-Ray Reflectivity

X-ray reflectivity (XRR) is used to determine the oxidation front at the nanometer scale in sputtered perpendicular semi tunnel junctions, as the form Pt/Co/AlO_x , by varying the oxidation time t_Ox of the capping layer. From XRR simulations, we show that the nature of the stack is gradually defined according to the value of t_Ox. For low t_Ox values (< 40 s), a simple Pt/Co/Al/AlO_x multilayer is appearing whereas a Pt/Co/CoO/AlO_x architecture takes place for higher t_Ox. The oxygen-induced magnetic properties obtained by extraordinary Hall effects measurements are explained by the structural results. The increase of Co-O bondings with t_Ox is at the origin of the appearing of the perpendicular magnetic anisotropy (PMA).