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학술연구/단체지원/교육 등 연구자 활동을 지속하도록 DBpia가 지원하고 있어요.
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Single-crystal hematite (α-Fe2O3) nanorings with three different thicknesses were synthesized by a hydrothermal method. The results of X-ray diffraction (XRD), transmission electron microscopy (TEM) and scanning electron microscopy (SEM) show that the nanorings are single-crystal and have relatively uniform outer diameters of 160 nm, and heights of about 100 nm. Magnetic measurements up to 920K have been performed on hydrothermally synthesized α-Fe2O3 nanorings and nanoparticles using a quantum design vibrating sample magnetometer. A high temperature phase transition of thermal stability ( α-Fe2O3 to Fe3O4) occurs when magnetic measurement was performed under high vacuum ( < 9.5 x 10-5 Torr). The phase transition temperature is 670 K for nanorings with thickness of ~30 nm, 718 K for nanorings with thickness of ~50 nm, 678 K for nanorings with thickness of ~65 nm, and 640 K for ~35 nm nanoparticles. This data show better thermal stability of nanorings with the thickness of ~50 nm than the other two kinds of nanoring samples The Néel temperature (TN) of α-Fe2O3 nanorings with the thickness of ~50 nm is determined to be 937.2 K by magnetic measurement for the first time, about 22.8 K below the bulk value. The small reduction of the TN of the α-Fe2O3 nanorings is consistent with the finite-size scaling theory.
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