Interfacial Spintronic THz Emission

Abstract

The broken inversion symmetry at the ferromagnet (FM)/heavy‐metal (HM) interface leads to spin‐dependent degeneracy of the energy band, forming spin‐polarized surface states. As a result, the interface serves as an effective medium for converting spin accumulation into 2D charge current through the inverse Rashba–Edelstein effect. Exploring and assessing this spin‐to‐charge conversion (SCC) phenomenon at the FM/HM interface can offer a promising avenue to surpass the presumed limits of SCC in bulk HM layers. Spintronic heterostructures are utilized as a platform to measure the SCC experienced by photoexcited spin currents. Therefore, FM/HM heterostructures emitting terahertz electric field upon illumination by femtosecond laser pulses enable quantitative measure of the ultrafast SCC process. This results demonstrate a robust interfacial spin‐to‐charge conversion (iSCC) within a synthetic antiferromagnetic heterostructure, specifically for the NiFe/Ru/NiFe configuration, by isolating the SCC contribution originating from the interface and the bulk heavy‐metal (HM). Through the measurements of the emitted terahertz pulse, the iSCC at the NiFe/Ru interface is identified to be ≈27% of the strength as compared to SCC from the highest spin‐Hall conducting heavy‐metal, Pt. The results thus highlight the significance of interfacial engineering as a promising pathway for achieving efficient ultrafast spintronic devices.