Fonin, M.; Dedkov, Yu. S.; Pentcheva, Rossitza; Rüdiger, U.; Güntherodt, G. (2007): Magnetite: A search for the half-metallic state. In: Journal of Physics Condensed Matter, Vol. 19, Nr. 31
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We present a detailed study of the spin-dependent electronic structure of thin epitaxial magnetite films of different crystallographic orientations. Using spin-and angle-resolved photoelectron spectroscopy at room temperature, we determine for epitaxial Fe3O4(111) films a maximum spin polarization value of -(80 5)\% near EF. The spin-resolved photoelectron spectra for binding energies between 1.5eV and EF show good agreement with the spin-split band structure from density functional theory (DFT) calculations which predict an overall energy gap in the spin-up electron bands in high symmetry directions, thus providing evidence for the half-metallic ferromagnetic state of Fe3O4 in the [111] direction. In the case of the Fe3O4(100) surface, both the spin-resolved photoelectron spectroscopy experiments and the DFT density of states give evidence for a half-metal to metal transition: the measured spin polarization of about -(55 10)\% at EF and the theoretical value of -40\% are significantly lower than the -100\% predicted by local spin density approximation (LSDA) calculations for the bulk magnetite crystal as well as the -(80 5)\% obtained for the Fe3O4(111) films. The experimental findings were corroborated by DFT calculations as due to a surface reconstruction leading to the electronic states in the majority-spin band gap and thus to the reduced spin polarization.