Fermi surface of the ferromagnetic semimetal,EuB6

We report the results of magnetoresistance and magnetization measurements on single crystal ${\mathrm{EuB}}_6$ for temperatures above and below the ferromagnetic ordering temperatures $T_C^{+}=15.3\mathrm{}\hspace{0.5em}\mathrm{K}$ and $T_C^{-}=12.5\mathrm{}\hspace{0.5em}\mathrm{K},$ in magnetic fields as large as 30 T. Shubnikov–de Haas and de Haas–van Alphen oscillations were observed with four fundamental frequencies. By comparison to band-structure calculations, we ascribe the orbits to small pockets of electrons and holes, centered at the X points. The effective masses and extremal areas of the pockets are in good agreement with the predictions of band-structure calculations. We conclude that ${\mathrm{EuB}}_6$ is an intrinsic semimetal and not a doped insulator. The intrinsic carrier concentration is $1.2\times {10}^{20}\hspace{0.5em}{\mathrm{cm}}^{-3},$ although our sample is somewhat uncompensated, with a 65% surplus of holes. There is no appreciable modification to the Fermi-surface dimensions or carrier masses with the onset of ferromagnetism.