Effects of MgO Barrier Thickness on Magnetic Anisotropy Energy Constant in Perpendicular Magnetic Tunnel Junctions of (Co/Pd)$_{n}$/MgO/(Co/Pt)$_{n}$

In this study, we report experimental results on perpendicular magnetic tunnel junctions composed of the binary multilayer Co/Pt and Co/Pd with various MgO barrier thicknesses. The coercivities of both Co/Pt and Co/Pd layers varied substantially with the MgO thickness. Very interestingly, the perpendicular anisotropy constant Ku of the Co/Pt multilayer measured by the extraordinary Hall effect oscillated with the MgO thickness, and the period of this oscillation was about 0.3 nm. Furthermore, both the Ku value and the oscillation amplitude decreased after annealing at 150
^deg
C and 200
^deg
C, which suggest that the oscillation may result from the film morphology.