Influence of Metal Interlayers on Spin-Charge Conversion in Sb₂Te₃ Topological Insulator-Based Devices

The magnetization of a ferromagnetic layer can be controlled via spin-charge conversion (SCC) phenomena originating in an adjacent topological insulator (TI). Insertion of nonmagnetic interlayers between these materials has been demonstrated to enhance the SCC efficiency, as shown for Sb₂Te₃/Au/Co(Fe) heterostructures. The inert nature of the Sb₂Te₃/Au interface was assumed to preserve the topological surface state (TSS) of Sb₂Te₃, which mediates the SCC. Al is explored as an alternative to Au for its long spin diffusion length. Spin pumping experiments indicate the absence of SCC in the Sb₂Te₃/Al/Co heterostructure. Core level and valence band photoemission spectroscopies reveal that Al forms stable compounds with Te and Sb, thereby quenching the TSS of Sb₂Te₃, while the TSS is preserved upon the formation of the TI/Au interface. These results demonstrate directly the major influence of material chemistry and highlight the role of TSS on the SCC efficiency in TI-based devices.