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Surfaces of half -metals

Camelia Borca, University of Nebraska - Lincoln

Abstract

The relationship between composition and electronic structure of half-metallic surfaces has been explored. The theoretical calculations of the electronic structure for a half-metal predict 100% spin-polarization at the Fermi level at 0 K. However, compelling evidence of half-metallic character has not yet been found. The work presented in this dissertation focuses on the interplay between surface composition and surface electronic structure of the NiMnSb Heusler alloy and the La0.65Pb0.35MnO3 (LPMO) perovskite compound. The results found in this study may be able to explain the reduced experimental values of spin-polarization found in the literature at the surface or interface regions of these materials. ^ The spin-polarized unoccupied band structure has been explored for the first time for a half-metallic surface. The stoichiometic (proper) or unreconstructed surfaces of NiMnSb and La0.65Pb0.35MnO3 show values close to 100% for polarization in the center of the Brillouin zone at room temperature—which is not enough to prove the half-metallic character. Surface segregation and restructuring induced by annealing treatments greatly reduces the polarization values for these types of materials. The proper NiMnSb surface shows, in particular, evidence of a moment reordering transition at a temperature around 80–100 K. The LPMO restructured surface has a reduced surface ordering temperature compared to the un-restructured surface. ^

Subject Area

Physics, Condensed Matter

Recommended Citation

Borca, Camelia, "Surfaces of half -metals" (2001). ETD collection for University of Nebraska - Lincoln. AAI3004607.
http://digitalcommons.unl.edu/dissertations/AAI3004607

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