Impact of Ta Diffusion on the Perpendicular Magnetic Anisotropy of Ta/CoFeB/MgO

Effects of Ta diffusion on the perpendicular magnetic anisotropy (PMA) of Ta/Co_0.6Fe_0.2B_0.2 (12.5 Å)/MgO stacks were investigated. We found that Ta initially mixed with Co_0.6Fe _0.2B_0.2 and its diffusion became prominent above 300 °C. Initial diffusion of Ta into the Co_0.6 Fe_0.2B_0.2 was not detrimental to the PMA, but a significant PMA reduction occurred when Ta migrated to the Co _0.6Fe_0.2 B_0.2/MgO interface. This accounts for the fact that optimizing the PMA of Ta/CoFeB/MgO requires the tuning of both CoFeB thickness and annealing temperature.