Temperature of the Magnetic Ordering of the Trivalent Iron Oxide epsilon-Fe2O3

The trivalent iron oxide ε-Fe₂O₃ is a fairly rare polymorphic iron oxide modification, which only exists in the form of nanoparticles. This magnetically ordered material exhibits an intriguing magnetic behavior, specifically, a significant room-temperature coercivity H_C (up to ~20 kOe) and a magnetic transition in the temperature range of 80–150 K accompanied by a sharp decrease in the H_C value. Previously, the temperature of the transition to the paramagnetic state for ε-Fe₂O₃ was believed to be about 500 K. However, recent investigations have shown that the magnetically ordered phase exists in ε-Fe₂O₃ also at higher temperatures and, around 500 K, another magnetic transition occurs. Using the data on the magnetization and temperature evolution of the ferromagnetic resonance spectra, it is shown that the temperature of the transition of ε-Fe₂O₃ particles 3–10 nm in size to the paramagnetic state is ~850 K.