Terahertz magneto-optical response in ferromagnetic Fe-Co-Al alloys.

We study the magneto-optical properties of Fe-Co-Al ordered alloys in the terahertz range of frequencies. Using the standard Kubo-based approach to compute intrinsic part of theσxy(ω)we find a strong dependence of σ xy on ω in the terahertz range. For example, we find that below 10 THz Co 3 Al has nearly constant σ xy and that above 10 THz it is reduced by about 50 times. Furthermore, we find a strong dependence of σ xy on the chemical composition. For example, we find that the addition of Al to Fe changes the sign of σ xy , while the addition of Co to Fe leads to a nonmonotonic dependence of σ xy on Co concentration.