Phonon-Mode Calculation, Far- and Mid-Infrared, and Raman Spectra of an ε-Ga0.5Fe1.5O3 Magnet

Gallium-substituted epsilon iron oxide (e-Ga0.5Fe1.5O3) has drawn attention because its millimeter wave absorption frequency meets the millimeter wave radar frequency for automobiles. We report the phonon modes of e-Ga0.5Fe1.5O3, which has an orthorhombic structure in the Pna21 space group. First-principles phonon-mode calculations show that e-Ga0.5Fe1.5O3 has 117 optical phonon modes (fundamental vibrations) with symmetries of A1, A2, B1, and B2 as well as three acoustic phonon modes. The phonon density of states demonstrates that the movements of Fe and Ga contribute to the phonon modes in the lower energy region of 20–370 cm–1, while the movements of O contribute to the phonon modes in the higher energy region of 370–720 cm–1. We directly measure the optical phonon modes of e-Ga0.48Fe1.52O3 nanoparticles using far- and mid-infrared (IR) and Raman spectroscopies, which agree well with those obtained by first-principles phonon-mode calculations. Additionally, the thermodynamic parameters of the internal ...