Magnetite: a search for the half-metallic state

Abstract

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 1.5 eV 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.(Some figures in this article are in colour only in the electronic version)