Verwey transition in epitaxial Fe3O4 films

Thin magnetite films grown on cleaved MgO (100) substrates were studied by in-situ conversion electron Mossbauer spectroscopy (CEMS) in the temperature range of 80 K-300 K. The film growth was monitored by low energy electron diffraction revealing a perfect epitaxy in the whole thickness range from 430 nm down to 3 nm. GEMS measurements proved an ideal magnetite stoichiometry of the 430 nm thick film reflected both in the hyperfine pattern and in the Verwey transition. The thinner films showed strong deviation from the bulk properties, which was attributed to the modification of composition at the MgO/Fe3O4 interface, at which a magnesium rich phase is supposed based on CEM spectra. This phase, which was not observed previously, could be detected thanks to highly sensitive low-temperature measurements.