Sol–Gel Synthesis and Micro-Raman Characterization of ε‑Fe₂O₃ Micro- and Nanoparticles

In this work, we present a sol–gel synthesis of ε-Fe₂O₃ nano and microparticles stabilized in silica thin films. Thanks to the relatively high size of the synthesized particles, we have been able to discriminate the Raman signal of the ε- and α-Fe₂O₃ phases, thus presenting the first Confocal Raman Microscopy study of isolated ε-Fe₂O₃ particles. The vibrational modes of each phase are identified at room temperature. The phase transition from ε- to α-Fe₂O₃ and the morphological modifications are analyzed as a function of the in situ output laser power. A complete study of the Raman spectra for ε-Fe₂O₃ particles has been performed for a wide range of temperatures (80–570 K). The phonon frequencies and line widths show a behavior in which the contributions from lattice thermal expansion and anharmonic interactions have to be considered. We have also identified a two-magnon mode in the ε-Fe₂O₃ phase. Its intensity increases close to the Néel transition (T_N) and persists well above it. This observation could be one of the few experimental examples of a paramagnon, i.e., a magnetic excitation in a paramagnetic state.