Surface electronic structure of the Fe3O4(100) : Evidence of a half-metal to metal transition

In situ prepared ${\mathrm{Fe}}_{3}{\mathrm{O}}_{4}(100)$ thin films were studied by means of scanning tunneling microscopy (STM) and spin-polarized photoelectron spectroscopy (SP-PES). The atomically resolved $(\sqrt{2}\ifmmode\times\else\texttimes\fi{}\sqrt{2})R45\ifmmode^\circ\else\textdegree\fi{}$ wavelike surface atomic structure observed by STM is explained based on density functional theory (DFT) and ab initio atomistic thermodynamics calculations as a laterally distorted surface layer containing octahedral iron and oxygen, referred to as a modified $B$ layer. The work-function value of the ${\mathrm{Fe}}_{3}{\mathrm{O}}_{4}(100)$ surface extracted from the cutoff of the photoelectron spectra is in good agreement with that predicted from DFT. On the ${\mathrm{Fe}}_{3}{\mathrm{O}}_{4}(100)$ surface both the SP-PES measurements and the DFT results show a strong reduction of the spin polarization at the Fermi level $({E}_{F})$ compared to the bulk density of states. The nature of the states in the majority band gap of the ${\mathrm{Fe}}_{3}{\mathrm{O}}_{4}$ surface layer is analyzed.