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According to density-functional calculations, half metallic ferromagnets are characterized by a gap in one of the two spin bands, i. e. by a complete polarization of the spin conductivity. However, correlation effects are always crucial in these materials as they introduce an incoherent spectrum in the gap which is pinned at the Fermi energy, so-called nonquasiparticle states. We show that an appropriate treatment of dynamical correlation effects is essential for a full understanding of the spin polarization in these materials. In particular, we discuss results from recent theoretical calculations compared with tunneling-conductance spectroscopy measurements in the full-Heusler Co$_2$MnSi. |
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