Temperature of the magnetic ordering of the trivalent iron oxide $\varepsilon$-Fe$_{2}$O$_{3}$

The trivalent iron oxide $\varepsilon$-Fe$_{2}$O$_{3}$ 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 $\sim$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 $\varepsilon$-Fe$_{2}$O$_{3}$ was believed to be about 500 K. However, recent investigations have shown that the magnetically ordered phase exists in $\varepsilon$-Fe$_{2}$O$_{3}$ 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 $\varepsilon$-Fe$_{2}$O$_{3}$ particles 3–10 nm in size to the paramagnetic state is $\sim$850 K.