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We present structural, magnetic, and optical properties of multiferroic hexagonal YbFeO3 thin films, deposited on single crystal (001) Al2O3 and (111) ysz substrates by a magnetron sputtering system. Interestingly, the thermal stress affects YbFeO3 films on Al2O3 and ysz very differently. Although hexagonal-YbFeO3/Al2O3 films changed from a hexagonal to an orthorhombic phase due to annealing above 1000 °C, hexagonal-YbFeO3/ysz films remained mostly unaffected even after annealing at 1200 °C. The electronic excitations of the YbFeO3 thin films are dominated by Fe3+ d to d on-site electronic excitations as well as O 2p to Fe 3d, Yb 6s, and 5d charge-transfer excitations, and these excitations for hexagonal-YbFeO3 and orthorhombic-YbFeO3 thin films are distinctly different, consistent with the crystal field environments in the hexagonal and orthorhombic phases of YbFeO3. The room temperature energy band gaps of the hexagonal-YbFeO3 and orthorhombic-YbFeO3 thin films were measured to be ∼1.95 ± 0.05 eV and ∼2.40 ± 0.05 eV, respectively. 

We report structural, optical, and electro-optical properties of polycrystalline YFe2O4 thin films, deposited on (0001) sapphire substrates using the electron-beam deposition technique. The optical spectra of a 120 nm YFe2O4 show Fe d to d on-site and O 2p to Fe 3d, Y 4d, and Y 5s charge-transfer electronic excitations. Anomalies in the temperature dependence data of the charge-transfer excitations and the splitting of the 4.46 eV charge-transfer peak strongly suggest a structural distortion at 180 ± 10 K. Evidence of such a structural distortion is also manifested in the surface resistance versus temperature data. In addition, the YFe2O4 thin film at low temperatures shows strong electro-optical properties, as high as 9% in the energy range of 1 - 2.5 eV, for applied electric fields up to 500 V.cm−1.