Decoupling Volume and Magnetic Anisotropy for the Enhancement of Thermal Stability in CoFeB Multilayered Structures

We demonstrate a fabrication strategy for multilayered CoFeB structures that overcomes the intrinsic trade‐off between magnetic volume and perpendicular magnetic anisotropy, enabling a substantial enhancement in thermal stability. In conventional CoFeB/MgO heterostructures, interfacial anisotropy restricts the ferromagnetic layer thickness, severely limiting the magnetic volume and thermal robustness. This limitation is eliminated using a continuous vacuum process combining thin‐film deposition, annealing, and an intermediate reverse‐sputtering step to remove temporary MgO layers. The resulting multilayer stacks consist of ferromagnetically coupled CoFeB layers separated by thin Ta interlayers, yielding a significantly increased effective magnetic volume. Compared with a single‐layer reference, the estimated thermal stability factor, calculated from the experimentally determined K eff and magnetic volume, is enhanced by 400%. The multilayer structure is intrinsically asymmetric, allowing direct integration with adjacent spin‐source layers for efficient net spin orbit torque‐driven magnetization switching. These results establish a viable route toward thermally robust perpendicular magnetic devices suitable for next‐generation spintronic applications.