Ferromagnetic Epitaxial μ-Fe2O3 on β-Ga2O3: A New Monoclinic form of Fe2O3

Here we demonstrate a new monoclinic iron oxide phase (μ-Fe2O3), epitaxially stabilized by growth on (010) β-Ga2O3. Density functional theory (DFT) calculations find that the lattice parameters of freestanding μ-Fe2O3 are within ~1% of those of β-Ga2O3 and that its energy of formation is comparable to that of naturally abundant Fe2O3 polytypes. A superlattice of μ-Fe2O3/β-Ga2O3 is grown by plasma assisted molecular beam epitaxy, with resulting high-resolution x-ray diffraction (XRD) measurements indicating that the μ-Fe2O3 layers are lattice-matched to the substrate. The measured out-of-plane (b) lattice parameter of 3.12 ± 0.4 A is in agreement with the predicted lattice constants and atomic-resolution scanning transmission electron microscopy (STEM) images comfirm complete registry of the μ-Fe2O3 layers with β-Ga2O3. Finally, DFT modeling predicts that bulk μ-Fe2O3 is antiferromagnetic, while the interface region between μ-Fe2O3 and β-Ga2O3 leads to ferromagnetic coupling between interface Fe3+ cations ...