Tuning Terahertz Emission via Interfacial Perpendicular Magnetic Anisotropy in Co/Gd/Co Spintronic Heterostructures

Spintronic terahertz (THz) emitters based on the inverse spin Hall effect (ISHE) are promising for ultrafast optoelectronic applications due to their high emission intensity and tunability. Among them, rare-earth (RE)–transition-metal (TM) ferrimagnetic systems stand out for their high thermal stability, robustness to magnetic interference, and ease of magnetization control. However, the nonmonotonic THz emission behavior observed with varying RE content or measurement temperature remains controversial. In this study, we systematically explore THz emission in Co/Gd/Co heterostructures with an engineered interfacial perpendicular magnetic anisotropy (PMA). By inserting an ultrathin Gd spacer layer (0.3–0.7 nm) between ferromagnetic Co layers, we observe a pronounced suppression in THz signal amplitude─mimicking the behavior of nearly compensated RE–TM alloys. Through a combined thickness-dependent analysis of Co and Gd layers, we attribute this suppression to strong interfacial PMA at the Co/Gd interface, which reduces the in-plane magnetization component necessary for efficient spin-to-charge conversion via the ISHE. Our results not only clarify the underlying mechanism responsible for THz emission minima in RE–TM systems but also highlight interfacial PMA as a key tuning parameter for optimizing spintronic THz emitter performance.