Perpendicular magnetic anisotropy of a Ta/NiFeB/MgO system and its magnetic coupling with [Pt/Co] multilayers

Highlights: • Stronger PMA is observed in Ta/NiFeB/MgO than in conventional in Ta/CoFeB/MgO. • PMA appears only after post-annealing. • Amorphous NiFeB transforms into bcc NiFe (001) upon post-annealing. • Ta/NiFeB/MgO is combined with [Pt/Co] multilayers to form even stronger PMA. -- Abstract: The perpendicular magnetic anisotropy (PMA) and crystalline structure of Ta/NiFeB/MgO stacks are investigated. When the stack is annealed, PMA is induced and the magnetic moment increases due to the crystallization of bcc NiFe from amorphous NiFeB. This structure is combined with [Pt/Co]₆ multilayers to study the change in the magnetic coupling and PMA behavior with the change in the Ta thickness inserted in-between and the annealing temperature. Among the [Pt/Co]₆/Ta/NiFeB/MgO stacks, the stack with a 0.5-nm-thick Ta layer shows the strongest PMA with an effective PMA energy density of 4.4 × 10⁶ erg/cm³ upon annealing at 400 °C. Further, the X-ray diffraction study of the crystalline structures confirms the formation of the NiFe (001) phase, which is essential for achieving a high tunneling magnetoresistance ratio.