The spin- and energy-dependent interface reflectivity of a ferromagnetic (FM) film in contact with a nonmagnetic (NM) film is calculated using a first-principles transport method and incorporated into the superdiffusive spin transport model to study the femtosecond laser-induced ultrafast demagnetization of $\mathrm{Fe}|\mathrm{NM}$ and $\mathrm{Ni}|\mathrm{NM}$ (NM = Au, Al, and Pt) bilayers. By comparing the calculated demagnetization with transparent and real interfaces, we demonstrate that the spin-dependent reflection of hot electrons has a noticeable influence on the ultrafast demagnetization and the associated terahertz (THz) electromagnetic radiation. In particular, a spin filtering effect is found at the $\mathrm{Fe}|\mathrm{NM}$ interface that increases the spin current injected into the NM metal, which enhances both the resulting demagnetization and the resulting THz emission. This suggests that the THz radiation can be optimized by tailoring the interface, indicating a very large tunability.

• Received 19 November 2019
• Revised 8 January 2020

DOI:https://doi.org/10.1103/PhysRevB.101.014435

Published by the American Physical Society under the terms of the Creative Commons Attribution 4.0 International license. Further distribution of this work must maintain attribution to the author(s) and the published article's title, journal citation, and DOI.

Published by the American Physical Society