Molecular beam epitaxy and ultraviolet Raman spectroscopy of hexagonal ScFeO₃ films

Hexagonal ScFeO₃ films synthesized by molecular beam epitaxy on (0001) oriented Al₂O₃ substrates were studied by variable temperature ultraviolet Raman spectroscopy. Films of varied thickness (10–150 nm) were grown in a monolayer controlled method by shuttering the MBE fluxes as well as by a co-deposition method so that the properties of the resulting films could be compared. The films were characterized by x-ray diffraction as well as atomic force microscopy. ScFeO₃ in the hexagonal phase (isostructural to YMnO₃ and other rare-earth ferrites) is predicted to be multiferroic near room temperature. This multiferroicity is a combination of ferroelectricity and antiferromagnetic order often seen in the family of rare-earth ferrites, but at significantly high temperatures in hexagonal ScFeO₃. The Raman spectra of hexagonal ScFeO₃ at room temperature are indicative of the polar hexagonal P6₃cm structure, in agreement with the x-ray diffraction spectra of the films, which are consistent with hexagonal ScFeO₃. The temperature evolution of the Raman spectra of hexagonal ScFeO₃ films over the range of 10-1450 K indicates a transition to a non-polar (likely P6₃/mmc) phase; fitting the integrated Raman intensities as a function of temperature yields a transition temperature of 950 K ± 50 K.