Magnetite: a search for the half-metallic state

• Published in: Journal of physics. Condensed matter Vol. 19; no. 31; pp. 315217 - 315217 (12)
• Main Authors: Fonin, M, Dedkov, Yu S, Pentcheva, R, Rüdiger, U, Güntherodt, G
• Format: Journal Article
• Language: English
• Published: England IOP Publishing 08.08.2007
• ISSN: 0953-8984; 1361-648X
• DOI: 10.1088/0953-8984/19/31/315217

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 Fe(3)O(4)(111) films a maximum spin polarization value of -(80 ± 5)% near E(F). The spin-resolved photoelectron spectra for binding energies between 1.5 eV and E(F) 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 Fe(3)O(4) in the [111] direction. In the case of the Fe(3)O(4)(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 E(F) 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 Fe(3)O(4)(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.