Incommensurate Growth of Thin and Ultrathin Films of Single-Phase Fe3O4(001) on SrTiO3(001)

We present structural, electronic, and morphological characterization of thin (7.5 nm, 9 unit cells) and ultrathin (1.7 nm, 2 unit cells) Fe3O4 layers grown on SrTiO3(001) by oxygen assisted molecular beam epitaxy (MBE) and pulsed laser deposition (PLD) methods. The analysis show single-phase single oriented (001) layers that grow forming a coincidence lattice of the order 13. Such an incommensurate growth is present for all the layers, independent of the evaporation method and layer thickness. The magnetite layers, which are strain-free, provide a sharp interface with the substrate. The films grown by the MBE method present negligible interaction with the substrate and smooth surfaces. The films grown by the PLD evaporation method present an expansion of the last atomic layer of the substrate and rough layer surface. However, the obtained structural domain size of 10 nm is identical for the layers grown by both evaporation techniques corresponding to the size of the coincidence lattice. We determine that the magnetic and transport properties inherent to the Fe3O4/STO heterostructure are not related to the lattice strain but to the formation of antiphase boundary defects.