Thermally stable perpendicular magnetic anisotropy features of Ta/TaOx/Ta/CoFeB/MgO/W stacks via TaOx underlayer insertion

We report that a TaOx underlayer enhances the stability of perpendicular magnetic anisotropy (PMA) in TaOx/Ta/CoFeB/MgO stacks during annealing; control of oxygen content in the TaOx layer is critical. X-ray photoelectron spectroscopy observations revealed clear suppression of Ta atom diffusion towards the CoFeB/MgO interface or MgO regions. The TaOx underlayer possibly served as a diffusion sponge, permitting some thermally activated Ta atoms to impregnate the TaOx underlayer via a diffusion path, such as grain boundaries. We propose a possible mechanism for enhanced PMA stability based on diffusion of thermally activated Ta atoms.