Using structural disorder to design terahertz optical response of ferromagnetic metal alloys

We study the intrinsic anomalous Hall conductivity of Fe-Co-Al alloys in the terahertz (THz) region by first-principles calculations. We find that alloying is a feasible way to tune the THz optical feature of ferromagnetic metals. The optical conductivity (sigma_xy) response of these alloys generically shows a lot of features in the range between 2 THz and 20 THz as it is driven by the spin-orbit interaction. In addition to sharp features in the spectrum, we also find that in some alloys sigma_xy can even change the sign in the THz regime.