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

In this work, we present a sol-gel synthesis of epsilon-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 epsilon- and alpha-Fe2O3 phases, thus presenting the first Confocal Raman Microscopy study of isolated epsilon-Fe2O3 particles. The vibrational modes of each phase are identified at room temperature. The phase transition from epsilon- to alpha-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 epsilon-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 epsilon-Fe2O3 phase. Its intensity increases close to the Neel 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.