R&D: Facile and Low-Temperature Synthesis of γ-Fe2O3 Nanoparticles With Thermally Stable Ferrimagnetism for Use in Magnetic Tapes

ACS Applied Nano Materials has published an article written by Takeshi Uyama, Kazuhiko Mukai, and Ikuya Yamada.

Abstract: “Maghemite, γ-Fe₂O₃, has regained importance as a magnetic tape storage material for the Big Data era due to its low cost and long-term durability. However, the conventional synthesis of γ-Fe₂O₃, which involves dehydration, reduction, and oxidation processes, is complicated and requires improvement. We synthesized γ-Fe₂O₃ directly via dehydration from the high-pressure phase of iron hydroxide, ϵ-FeOOH, using a low-temperature solution method. Bulk ϵ-FeOOH prepared from α-FeOOH at 8.2 GPa and 773 K transformed into γ-Fe₂O₃ in a 2-phenoxyethanol and LiOH●H₂O mixture at 498 K, which is the lowest such temperature among similar dehydration reactions. ⁵⁷Fe Mössbauer, Raman, and Fourier-transform infrared spectroscopic analyses revealed that the obtained γ-Fe₂O₃ particles were covered with amorphous lithium phases, which stabilized their ferrimagnetism with a magnetization of 61.9 emu g⁻¹ up to 1273 K, by converting to ferrimagnetic Li_0.5Fe_2.5O₄. Furthermore, we reduced the size of γ-Fe₂O₃ to an average of 0.5 µm and a minimum of approximately 100 nm by applying ϵ-FeOOH nanoparticle as a precursor, which was prepared under higher-pressure (10 GPa) and lower-temperature (673 K) conditions. Although synchrotron X-ray diffraction measurements found that the γ-Fe₂O₃ nanoparticles were contaminated with ion-exchanged α-LiFeO₂ at 80 wt%, a facile and low-temperature method to synthesize γ-Fe₂O₃ was established.“