  We have monitored the Verwey transition in micrometer-wide, nanometer-thick
magnetite islands on epitaxial Ru films on Al2O3(0001) using Raman
spectroscopy. The islands have been grown by high-temperature oxygen-assisted
molecular beam epitaxy. Below 100 K and for thicknesses above 20 nm the Raman
spectra correspond to those observed in bulk crystals and high quality thin
films for the sub-Verwey magnetite structure. At room temperature the width of
the cubic phase modes is similar to the best reported in bulk crystals,
indicating a similar level of electron-phonon interaction. The evolution of the
Raman spectra upon cooling suggests that for islands thicker than 20 nm,
structural changes appear first at temperatures starting at 150 K and the
Verwey transition itself takes place at around 115 K. However, islands thinner
than 20 nm show a very different Raman spectra indicating that while a
transition takes place, the charge order of the ultrathin islands differs
markedly from their thicker counterparts
