Charge dynamics and possibility of ferromagnetism in (formula presented) (formula presented) and Sr)

Ferromagnetism was recently reported in La-doped alkaline-earth hexaborides (formula presented) (formula presented) Sr, and Ba). We have performed reflectivity, Hall resistivity, and magnetization measurements of (formula presented) The results indicate that (formula presented) can be regarded as a simple doped semimetal, with no signature of an excitonic state as suggested by several theories. It is also found that the surface of as-grown samples (formula presented) in thickness) has a different electronic structure from a bulk one, and a fairly large number of paramagnetic moments are confined in this region. After eliminating these paramagnetic moments at the surface, we could not find any evidence of an intrinsic ferromagnetic moment in our samples, implying the possibility that the ferromagnetism of (formula presented) reported so far is not intrinsic.