Ferromagnetic enhances terahertz emission through the inverse orbital Hall effect in bilayers
Phys. Rev. Applied 24, 024009 – Published 5 August, 2025
DOI: https://doi.org/10.1103/j7gy-6jn8
Abstract
Spintronic terahertz (THz) emitters, utilizing ferromagnets/nonferromagnetic metal heterostructures, offer significant potential across imaging, communication, sensing, and material detection. To investigate whether the femtosecond laser-induced spin current and/or orbital current from ferromagnets can emit THz waves through the inverse spin Hall effect or inverse orbital Hall effect in nonferromagnetic metals, we focused on the heterostructures. These structures exhibit a negligible inverse spin Hall effect but a pronounced inverse orbital Hall effect in the layers, allowing us to explore the function of ferromagnets as the optimal laser-excited orbital current source. By examining the THz amplitude as a function of thickness, we determine that the orbital current diffusion length in is around 57.7 nm. Additionally, we employ the second-harmonic Hall resistance method to derive the thickness-dependent orbital Hall angle in the layers, based on the conversion of electric charge current to orbital current. Notably, the results from this method are highly consistent with those from THz emission measurements, indicating that the interconversion between orbital current and charge current is equivalent not only on picosecond timescales but also nearly instantaneously. Furthermore, by comparing the substantial THz amplitude emitted from heterostructures, which feature a significant spin Hall effect in layers, with that of , we confirm that also serves as an effective laser-excited spin-current source. Our findings indicate that utilizing materials with substantial orbital Hall angles and/or spin Hall angles in -based heterostructures could enhance the emission of THz waves.
