Signature of structural distortion in optical spectra of YFe₂O₄ thin film

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.