Evolution of the interfacial magnetic anisotropy in MgO/CoFeB/Ta/Ru based multilayers as a function of annealing temperature

We report effect of the annealing temperature on the dynamic and static magnetic properties of MgO/CoFeB/Ta/Ru multilayers. The angular resolved ferromagnetic resonance measurements results show that the as-deposited film exhibits in-plane magnetic anisotropy, whereas in the annealed films the magnetic easy-axis is almost along the direction perpendicular to the plane of the layers. The extracted interfacial anisotropy energy, Ki, is maximized at an annealing temperature 225 °C, in agreement with the vibrating sample magnetometry results. Although the magnetization is not fully out-of-plane, controlling the degree of the magnetization obliquity may be advantageous for specific applications such as spin-transfer oscillators.