Abstract
We study the stability, magnetic order, charge segregation, and electronic properties of a novel three-layered Fe3O4 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 Fe2+ ions in the center layer and Fe3+ 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.
Highlights
Ultrathin transition metal oxide films are of significant interest for a wide range of intriguing applications in different disciplines, ranging from heterogeneous catalysis [1,2,3] to spintronics [4] and advanced electronics [5,6,7]
Through a Bader charge analysis [23] we find that the Fe ions in the center layer correspond to Fe2+, while the ions at the surfaces are of the Fe3+ type
To study the structure and magnetic order that minimize the total energy for the TOT1 structure, we computed the energy for the five aforementioned spin configurations as a function of the in-plane lattice parameters
Summary
Ultrathin transition metal oxide films are of significant interest for a wide range of intriguing applications in different disciplines, ranging from heterogeneous catalysis [1,2,3] to spintronics [4] and advanced electronics [5,6,7]. The properties of the films can be further tailored by the interaction with metal substrates, which alter the coordination and bonding and thereby affect the overall physical properties [7,8,9,10] This would in principle provide a means for designing, or customizing, composite systems comprising a transition metal oxide film and an appropriate metal support to meet the desired properties for specific applications. Successful examples along this line of research include the combination of an FeO(111) monolayer on a Pt(111) substrate, for which it has been found that the low-temperature catalytic activity for CO was improved compared to that of pure Pt(111) [9,10,11,12,13].
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