Magnetic measurements up to 1000 K have been performed on hydrothermally synthesized $alpha$-Fe$_{2}$O$_{3}$ nanoparticles (60 nm) using a Quantum Design vibrating sample magnetometer. A high vacuum environment (1$times$10$^{-5}$ torr) during the mag
netic measurement up to 1000 K leads to a complete reduction of $alpha$-Fe$_{2}$O$_{3}$ to Fe$_{3}$O$_{4}$. This precludes the determination of the Neel temperature for the $alpha$-Fe$_{2}$O$_{3}$ nanoparticles. In contrast, coating $alpha$-Fe$_{2}$O$_{3}$ nanoparticles with SiO$_{2}$ stabilizes the $alpha$-Fe$_{2}$O$_{3}$ phase up to 930 K, which allows us to determine the Neel temperature of the $alpha$-Fe$_{2}$O$_{3}$ nanoparticles for the first time. The Neel temperature of the 60-nm $alpha$-Fe$_{2}$O$_{3}$ nanoparticles is found to be 945 K, about 15 K below the bulk value. The small reduction of the Neel temperature of the $alpha$-Fe$_{2}$O$_{3}$ nanoparticles is consistent with a finite-size scaling theory. Our current results also show that coating nanoparticles with SiO$_{2}$ can effectively protect nanoparticles from oxidation or reduction, which is important to technological applications.
