Effects of growth order on perpendicular magnetic anisotropy of heavy metal/ferromagnet/MgO tri-layered structures

Previous experiments have shown that perpendicular magnetic anisotropy (PMA) in trilayers consisting of a CoFeB layer, an MgO layer, and a nonmagnetic metal (NM) layer depends strongly on whether the CoFeB layer was grown on the top of an NM layer or was capped by an NM layer. In this letter, we study the physical origin of this phenomenon through first-principles calculations. We took MgO/CoFe/Ta and Ta/CoFe/MgO as model structures and analyzed the magnetic anisotropy energy (MAE) therein. The “substrate/Ta/CoFe/MgO” structure had a notably higher MAE than the “substrate/MgO/CoFe/Ta” structure. This difference results mainly from different stresses in the Ta layers, and the latter gives rise to a difference in the hybridization strength of in-plane orbits ( ${d_{xy}}, {d_{{x^2} - {y^2}}}, {p_x},$ and ${p_y}$ ). The $p$ -orbital hybridization in the Ta layers contributes significantly to the PMA in both structures.