FERMI SURFACE OF THE FERROMAGNETIC SEMIMETAL, EUB6

We report the results of magnetoresistance and magnetization measurements on single crystal EuB{sub 6} for temperatures above and below the ferromagnetic ordering temperatures T{sub C}{sup +}=15.3 K and T{sub C}{sup {minus}}=12.5 K, in magnetic fields as large as 30 T. Shubnikov{endash}de Haas and de Haas{endash}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 {ital 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 EuB{sub 6} is an intrinsic semimetal and not a doped insulator. The intrinsic carrier concentration is 1.2{times}10{sup 20} cm{sup {minus}3}, although our sample is somewhat uncompensated, with a 65{percent} surplus of holes. There is no appreciable modification to the Fermi-surface dimensions or carrier masses with the onset of ferromagnetism. {copyright} {ital 1999} {ital The American Physical Society}