Electronic and magnetic properties of ultra-thin epitaxial magnetite films on MgO(001)

The electronic and magnetic properties of epitaxial Fe3O4 (001) films on MgO(100) substrates were studied throughout the 2.5- to 30-nm thickness range using conversion electron Mössbauer spectroscopy. Despite the superparamagnetism that was observed for film thickness below 5 nm, the Verwey transition persisted even for the thinnest film. Temperature-dependent Mössbauer measurements between 80 K and 400 K revealed that the activation energy for the magnetic moment fluctuations in the 3-nm magnetite film is higher than the magnetic anisotropy energy by an order of magnitude.