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Z. Novotny, N. Mulakaluri, Z. Edes, M. Schmid, R. Pentcheva, U. Diebold, G. Parkinson:
"Probing the surface phase diagram of Fe₃O₄(001) towards the Fe-rich limit: Evidence for progressive reduction of the surface";
Physical Review B, 87 (2013), 1954101 - 1954108.

Reduced terminations of the Fe3O4(001) surface were studied using scanning tunneling microscopy,
x-ray photoelectron spectroscopy (XPS), and density functional theory (DFT). Fe atoms, deposited onto the
thermodynamically stable, distorted B-layer termination at room temperature (RT), occupy one of two available
tetrahedrally coordinated sites per (
√
2 ×
√
2)R45◦ unit cell. Further RT deposition results in Fe clusters. With
mild annealing, a second Fe adatom per unit cell is accommodated, though not in the second tetrahedral site.Rather
both Fe atoms reside in octahedral coordinated sites, leading to a "Fe-dimer" termination. At four additional Fe
atoms per unit cell, all surface octahedral sites are occupied, resulting in a FeO(001)-like phase. The observed
configurations are consistent with the calculated surface phase diagram. Both XPS and DFT+U results indicate
a progressive reduction of surface iron from Fe3+ to Fe2+ upon Fe deposition. The antiferromagnetic FeO layer
on top of ferromagnetic Fe3O4(001) suggests possible exchange bias in this system.