Fermi surface of the ferromagnetic semimetal, EuB₆

We report the results of magnetoresistance and magnetization measurements on single crystal EuB₆ for temperatures above and below the ferromagnetic ordering temperatures T_C⁺=15.3 K and T_C^-=12.5 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 EuB₆ is an intrinsic semimetal and not a doped insulator. The intrinsic carrier concentration is 1.2×10²⁰ 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.