Spin polarization of the ferromagnetic semimetal EuB$_{6}$

Much progress has been made recently in the understanding of the electronic properties of EuB$_{6}$. However, the details of the electronic structure remain controversial. Several band structure calculations have produced different degrees of conduction-valence band overlap for the two spin subbands. In particular, some calculations predict a half-metallic band structure, ie, 100{\%} spin polarization at the Fermi level$^{1}$. We have performed direct measurements of the spin polarization of EuB$_{6}$ crystals using Andreev reflection spectroscopy. Planar junctions of EuB$_{6}$/Pb were fabricated on crystals grown with an Al flux method. The conductance spectra were measured using phase-sensitive detection at several temperatures below T$_{C}$ of Pb. The spectra are well-described by the spin-polarized BTK model. More than seven junctions were measured and a spin polarization of 55 $\pm $ 10{\%} is obtained. Our results indicate that in ferromagnetic EuB$_{6}$ the electrons and holes at the Fermi level are not fully spin-polarized. This work was supported by a FSU Research Foundation PEG grant and NSF grant under DMR-0503360. $^{1}$J. Kunes and W.E. Pickett, PRB 69, 165111 (2004); M. Kreissle and W. Nolting, PRB 72, 245117 (2005).