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 the sigma x y ( omega ) we find a strong dependence of sigma xy on omega in the terahertz range. For example, we find that below 10 THz Co3Al has nearly constant sigma xy and that above 10 THz it is reduced by about 50 times. Furthermore, we find a strong dependence of sigma xy on the chemical composition. For example, we find that the addition of Al to Fe changes the sign of sigma xy , while the addition of Co to Fe leads to a nonmonotonic dependence of sigma xy on Co concentration.