  Crystalline Fe3O4/NiO bilayers were grown on MgO(001) substrates using
reactive molecular beam epitaxy to investigate their structural properties and
their morphology. The film thickness either of the Fe3O4 film or of the NiO
film has been varied to shed light on the relaxation of the bilayer system. The
surface properties as studied by x-ray photo electron spectroscopy and low
energy electron diffraction show clear evidence of stoichiometric well-ordered
film surfaces. Based on the kinematic approach x-ray diffraction experiments
were completely analyzed. As a result the NiO films grow pseudomorphic in the
investigated thickness range (up to 34nm) while the Fe3O4 films relax
continuously up to the thickness of 50nm. Although all diffraction data show
well developed Laue fringes pointing to oxide films of very homogeneous
thickness, the Fe3O4-NiO interface roughens continuously up to 1nm
root-mean-square roughness with increasing NiO film thickness while the Fe3O4
surface is very smooth independent on the Fe3O4 film thickness. Finally, the
Fe3O4-NiO interface spacing is similar to the interlayer spacing of the oxide
films while the NiO-MgO interface is expanded.
