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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 magnetic 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.
Single-crystalline alpha-Fe2O3 nanorings (short nanotubes) and nanotubes were synthesized by a hydrothermal method. High-resolution transmission electron microscope and selected-area electron diffraction confirm that the axial directions of both nano
Finite size effect on the antiferromagnetic transition temperature, TN, of Co3O4 nanoparticles of 75, 35, and 16 nm in diameter, has been investigated. The AFM transition point, TN, reduces with the decreasing diameter, d. Along with the results from
Tetragonal beta-FeSe obtained by hydrothermal reaction is not superconducting and transforms to a triclinic structure at 60 K unlike superconducting FeSe from solid state synthesis, which becomes orthorhombic at 90 K. In contrast, tetragonal iron sul
The production of hydrogen from water using only a catalyst and solar energy is one of the most challenging and promising outlets for the generation of clean and renewable energy. Semiconductor photocatalysts for solar hydrogen production by water ph
Vortices are among the simplest topological structures, and occur whenever a flow field `whirls around a one-dimensional core. They are ubiquitous to many branches of physics, from fluid dynamics to superconductivity and superfluidity, and are even p