Phonon and magnon modes in preferentially oriented epitaxial α-Fe2O3 thin films investigated by Raman spectroscopy

Abstract

Polarization- and temperature-dependent Raman spectroscopy of epitaxial α-Fe₂O₃ films revealed anisotropic phonon-magnon dynamics and spin–phonon coupling. Resonant excitation at 2.33 eV selectively enhanced the E_2u(LO) mode via a defect-mediated double-resonance process, while the first-order E_1u(LO) phonon exhibited single-phonon scattering. Polarization-resolved Raman spectra showed systematic angular variations in intensity I(θ), frequency ω(θ), and linewidth Γ(θ), arising from symmetry-selective electron–phonon coupling and decay pathways in the trigonal D⁶_3d structure. A_g phonon modes followed cos² θ behavior, confirming c-axis orientation, while E_g modes showed off-diagonal tensor coupling. Temperature studies across the Morin transition (T_M) revealed renormalization of phonon frequency and linewidth and enhanced magnon intensity above T_M due to spin canting, with low-energy A_g and E_g modes exhibited the most pronounced spin–phonon coupling.