Stability, magnetic order, and electronic properties of ultrathin Fe3O4 nanosheets

Abstract

We study the stability, magnetic order, charge segregation, and electronic properties of a novel three-layered Fe 3 O 4 film by means of Hubbard-corrected density functional theory calculations. The stable film is predicted to consist of close-packed iron and oxygen layers, comprising a center layer with octahedrally coordinated Fe sandwiched between two layers with tetrahedrally coordinated Fe. The film exhibits an antiferromagnetic type I spin order. A charge analysis confirms that the stable structure has distinct charge segregation, with Fe 2+ ions in the center layer and Fe 3+ in the tetrahedral surface layers. Examination of the electronic band structures and densities of states shows that the bandgap is substantially reduced, from 2.4 eV for the bulk rocksalt to 0.3 eV for the film. The reduction in the bandgap is a consequence of the 2+ to 3+ change in oxidation state of Fe in the surface layers.

Structure of two-dimensional Fe3O4

“…Details of the investigation of charge and spin distributions will be described separately. 61 Figure 6 shows the total and projected densities of states calculated for the TOT1 Fe 3 O 4 sheet with antiferromagnetic spin ordering. The DFT+U calculations predict a small, indirect bandgap of 0.3 eV separating filled 3d states on the central Fe 2+ oct sites from empty 3d states at the outer Fe 3+ tet sites.…”

Frenkel pair formation energy for cubic Fe$_3$O$_4$ in DFT+U calculations

“…The accuracy is rather high and is typical for DFT+U (e.g. 44 ). Only the hybrid HSE06 functional was shown to give a better accuracy 27 .…”