Half-metallicity in NiMnSb: A variational cluster approach with ab initio parameters

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2010

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Electron correlation effects in the half-metallic ferromagnet NiMnSb are investigated within a combined density functional and many-body approach. Starting from a realistic multiorbital Hubbard model including Mnd and Nid orbitals, the many-body problem is addressed via the variational cluster approach using, as a reference system, a two-site cluster containing one manganese and one nickel site. The density of states obtained in the calculation shows a strong spectral-weight transfer toward the Fermi level in the occupied conducting majority spin channel with respect to the uncorrelated case, as well as states with vanishing quasiparticle weight in the minority-spin gap. Although the two features produce competing effects, the overall outcome is a strong reduction in the spin polarization at the Fermi level with respect to the uncorrelated case. Our results indicate the presence of substantial nonlocal correlation effects in the low-energy range for minority-spin electrons. More specifically, the imaginary part of the self-energy between Mn (t2g) and Ni (t2g) orbitals is significantly larger than local contributions at those energies. This emphasizes the importance of nonlocal correlations in this material. © 2010 The American Physical Society.

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