Enhanced tunneling magnetoresistance and thermal stability in magnetic tunnel junctions with multiple CoFeB/Ta interfaces

We present a comparative study of perpendicular magnetic tunnel junctions (p-MTJs) incorporating either a single CoFeB free layer or a double free layer structure consisting of two 1.2 nm CoFeB layers separated by a 0.3 nm Ta spacer. Remarkably, despite the increased total magnetic thickness, the double free layer preserves strong perpendicular magnetic anisotropy (PMA), underscoring the robustness of interfacial anisotropy in these systems. After annealing at 320 °C, the CoFeB/Ta/CoFeB composite free layer shows and increase of TMR by ~ 50% relative to the single‑CoFeB free layer and maintains significantly higher TMR at elevated annealing temperatures, indicating a broadened annealing window. These results highlight the potential of multilayer CoFeB-based free layer designs for enabling thermally robust, high-performance spintronic devices.