This study presents an innovative approach to optimizing perpendicular magnetic anisotropy (PMA) in CoFeB/MgO structures through the strategic insertion of an ultrathin CoFeB layer between the top capping layer (Ta or Mo) and the CoFeB/MgO stack. Adding a 0.43 nm CoFeB insertion layer significantly enhances PMA by improving Fe-O hybridization, suppressing interfacial diffusion, and stabilizing MgO crystallinity. Postannealing at 400 °C, the CoFeB (free)/MgO (capping)/CoFeB (0.43 nm insertion layer)/Ta (top capping) configuration demonstrates superior performance, achieving an interfacial anisotropy constant (