Electronic transport inEu1−xCaxB6

We have measured the electrical resistivity, the magnetoresistance, the Hall effect, and the magnetization in varying temperature ranges between 0.3 and 300 K on single crystals of ${\mathrm{EuB}}_6,$ ${\mathrm{CaB}}_6,$ and ${\mathrm{Eu}}_{0.8}{\mathrm{Ca}}_{0.2}{\mathrm{B}}_6.$ The ferromagnetic phase transition of ${\mathrm{EuB}}_6,$ marked by a sharp peak in the temperature dependence of the electrical resistivity $\rho \mathrm{}\left(T\right)\mathrm{}$ just below 16 K, is shown to be accompanied by a considerable increase of the effective charge carrier concentration $n_{\mathrm{eff}}.$ The overall features of the transport properties of ${\mathrm{Eu}}_{0.8}{\mathrm{Ca}}_{0.2}{\mathrm{B}}_6$ are similar to those of ${\mathrm{EuB}}_6.$ A phase transition at 5.3 K has been established. However, the increase of $n_{\mathrm{eff}}$ across this phase transition by two orders of magnitude is much more pronounced than in pure ${\mathrm{EuB}}_6.$