Electronic and magnetic structure of epitaxial NiO/Fe3O4(001) heterostructures grown on MgO(001) and Nb-doped SrTiO3(001)
Abstract
We study the underlying chemical, electronic and magnetic properties of a number of magnetite based thin films. The main focus is placed onto NiO/Fe3O4(001) bilayers grown on MgO(001) and Nb-SrTiO3(001) substrates. We compare the results with those obtained on pure Fe3O4(001) thin films. It is found that the magnetite layers are oxidized and Fe3+ dominates at the surfaces due to maghemite (γ-Fe2O3) formation, which decreases with increasing magnetite layer thickness. From a layer thickness of around 20 nm on the cationic distribution is close to that of stoichiometric Fe3O4. At the interface between NiO and Fe3O4 we find the Ni to be in a divalent valence state, with unambiguous spectral features in the Ni 2p core level x-ray photoelectron spectra typical for NiO. The formation of a significant NiFe2O4 interlayer can be excluded by means of XMCD. Magneto optical Kerr effect measurements reveal significant higher coercive fields compared to magnetite thin films grown on MgO(001), and a 45 rotated magnetic easy axis. We discuss the spin magnetic moments of the magnetite layers and find that the moment increases with increasing thin film thickness. At low thickness the NiO/Fe3O4 films grown on Nb-SrTiO3 exhibits a significantly decreased spin magnetic moments. A thickness of 20 nm or above leads to spin magnetic moments close to that of bulk magnetite.
Turn this paper into a lesson
ArcXiv compiles a structured reading guide from this paper's metadata: plain-English importance, contributions, prerequisite concepts, which sections to read first, flashcards, and a quiz. Grounded in the abstract, never invented.