Magneto-optical Kerr effect in Eu_1-xCa_xB₆

We have measured the magneto-optical Kerr rotation of ferromagnetic Eu_1-xCa_xB₆ with x=0.2 and 0.4, as well as of YbB₆ serving as the nonmagnetic reference material. As previously for EuB₆, we could identify a feature at 1 eV in the Kerr response which is related with electronic transitions involving the localized 4 f electron states. The absence of this feature in the data for YbB₆ confirms the relevance of the partially occupied 4 f states in shaping the magneto-optical features of Eu-based hexaborides. Disorder by Ca-doping broadens the itinerant charge carrier contribution to the magneto-optical spectra.