A very large perpendicular magnetic anisotropy in Pt/Co/MgO trilayers fabricated by controlling the MgO sputtering power and its thickness

Abstract

The perpendicular magnetic anisotropy (PMA) properties of Pt/Co/MgO trilayers are investigated as a function of the MgO sputtering power (P-MgO) and its thickness (t(MgO)), both of which are important parameters affecting the degree of oxygen interpenetration into Co during sputtering. A strong PMA is achieved at small values of P-MgO and t(MgO), where the oxygen interpenetration into Co is expected to be small. The range of oxygen interpenetration is relatively extended in such a way that it affects both the Pt/Co and Co/MgO interfaces. The PMA properties of as-deposited samples are improved by post-annealing for temperatures up to 400 degrees C examined in this study, probably due to the diffusion of the interpenetrated oxygen atoms toward the Co/MgO interface. In a structure of Pt/Co (0.6 nm)/MgO (2 nm), which is fabricated at P-MgO = 50 W and then annealed at 400 degrees C, a huge saturation field is achieved (over 40 kOe) indicating a very strong PMA. Between the two interfaces of Pt/Co and Co/MgO, the PMA is mainly due to the former in the as-deposited state, but the contribution of the latter increases with the increase in the annealing temperature.