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 present magnetic and electrical transport properties such as resistivity, magnetoresistance, dielectric, and polarization of polycrystalline YbFe2O4. The ferrimagnetic transition temperature is measured at 243 K, followed by the two low-temperature transitions at ∼190 K and ∼65 K, respectively. The magnetic properties including the M-H hysteresis loops exhibit a strong temperature dependence and possibly indicate a spin-glass state below 65 K for YbFe2O4. The iron Mössbauer measurement at 295 K confirms the presence of two Fe sites. The measured resistivity can be modeled with the Mott's variable-range hopping model, ρ ∝ exp(T0/T ) 1/4 , indicating the electron hopping between Fe 2+ and Fe 3+ sites. The magnetoresistance effects up to 6% at 8 T were observed and the effects could be caused by the field-induced changes in the electron hopping processes. The frequency-dependent complex dielectric constant has been found to be strongly influenced by the contact effects, and the polarization of polycrystalline YbFe2O4 does not show ferroelectricity.
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