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The capping agent plays a critical function in anisotropic crystal growth to induce polyhedral morphology of a nanocrystal. Uniform and single-crystalline α-Fe2O3 polyhedral nanoparticles in the hexagonal single crystal system named truncated hexagonal bipyramid for the first time were successfully synthesized by a facile one-step hydrothermal method with the aid of carboxymethyl cellulose and hydrazine molecules. The appearance and crystal structure of these iron oxide nanoparticles were characterized in detail by physicochemical methods. The results show that the as-synthesized α-Fe2O3 particles are bound by 12 same-side crystalline facets {101} and two other same facets {001} at the tops. These obtained iron oxide particles belong to a pure hematite phase, and the particle size is around 400 nm. The optical property of the as-synthesized product was analyzed, and the determined indirect band gap value E g is 2.08 eV. The magnetic property studies of truncated hexagonal bipyramid hematite particles have shown that this kind of α-Fe2O3 possess a weak ferromagnetism under the T M, and the saturation points do not reach up to the maximum applied magnetic field. Role of the reactants was discussed and investigated systematically in the work. Furthermore, a schematic illustration for the probable formation of this α-Fe2O3 morphology in whole of the synthetic process was also proposed.

Magnetically doped topological insulators have been significantly researched for unlocking the nontrivial topological phases and the resultant potential applications for spintronics. We report the effect of antiferromagnetic order induced by Gd substitution on the electronic properties of GdxBi2−xSe3 single crystals by analyzing the Shubnikov-de Haas oscillations. Antiferromagnetic order of Gd ions affects the 2D surface state in Bi2Se3 and changes the effective mass and lifetime of charge carriers. These observations suggest a strong correlation of 2D surface electrons with the antiferromagnetic ordering, where the itinerant electrons are bound to the Gd ions to mediate the antiferromagnetic interaction.

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