Charge dynamics and possibility of ferromagnetism in $A_{1-x}{\mathrm{La}}_x{\mathrm{B}}_6$ $(A=\mathrm{Ca}$ and Sr)

Ferromagnetism was recently reported in La-doped alkaline-earth hexaborides $A_{1-x}{\mathrm{La}}_x{\mathrm{B}}_6$ $(A=\mathrm{Ca},$ Sr, and Ba). We have performed reflectivity, Hall resistivity, and magnetization measurements of $A_{1-x}{\mathrm{La}}_x{\mathrm{B}}_6.$ The results indicate that $A_{1-x}{\mathrm{La}}_x{\mathrm{B}}_6$ 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 $(\sim 10\hspace{0.5em}\mu \mathrm{m}$ 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 $A_{1-x}{\mathrm{La}}_x{\mathrm{B}}_6$ reported so far is not intrinsic.