The nanocapsules with crystalline cores of GdAl 2 compound and shells of amorphous Al 2 O 3 were prepared by evaporating Gd x Al 100−x ͑x = 50, 60, 70, 80, and 90͒ alloys using a modified arc-discharge technique. The morphologies, average sizes, lattice constants, and surface characteristics of GdAl 2 /Al 2 O 3 nanocapsules were studied in detail by means of x-ray diffraction, energy dispersive spectroscopy, x-ray photoelectron spectroscopy, and high-resolution transmission electron microscopy. The formation mechanism of the nanocapsules was analyzed in detail. The differences in Curie temperatures and anisotropy constants of these nanocapsules were discussed with respect to their different structural characteristics. From 180 to 5 K, the magnetic entropy change of the GdAl 2 /Al 2 O 3 nanocapsules continuously increases with decreasing temperature T and rapidly enhances when the temperature tends to 5 K. The largest entropy change −⌬S at 7.5 K can respectively reach 18.02, 18.71, and 31.01 J kg −1 K −1 by varying the magnetic field from 7 to 1 T for the nanocapsules synthesized by arc-discharging Gd 70 Al 30 , Gd 80 Al 20 , and Gd 90 Al 10 alloys. The appearance of a large entropy change at low temperatures was ascribed to a lower anisotropy energy barrier and a high magnetic-moment density of the nanocapsules. The linear relation between the magnetic entropy change and the reciprocal of the temperature ͑1/T͒ was discussed in terms of superparamagnetism and magnetocaloric theory.

One‐dimensional nanorods of cubic aluminum oxide (γ‐Al2O3) have been synthesized by DC electric arc discharge of Fe and Al powders. It is seen that the diameters of the γ‐Al2O3 nanorods are relatively uniform, ranging from 20 to 30 nm. On the basis of detailed transmission electron microscopic observation, it is proposed that the growth of a γ‐Al2O3 nanorod follows the vapor–liquid–solid (VLS) process assisted by a two‐dimensional vapor–solid (VS) nucleation and growth mechanism. The features of heavy twinning in the nanorod imply that twins might contribute to the growth of the nanorod and serve as the nucleus of the nanorod. (© 2006 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

Segmented ZnS nanocones have been prepared at 1200 °C by thermal evaporation of zinc sulfide powders and catalyst metal tin. The as-synthesized products have been studied by energy-dispersive x-ray spectroscopy, selected-area electron diffraction, and high-resolution transmission electron microscopy. Microstructure characterization indicates that the formation of segmented nanocones can be attributed to the effects of regular twins structure. Theoretical analysis reveals that the nonuniform cross sections of nanocones are related to the continuous change of Sn–ZnS liquid droplet’s scale resulting from the supply of Sn atoms during the evaporation. According to microstructure characterization and dimension analysis, the potential formation mechanism of the segmented ZnS nanocones was discussed.

The magnetic and electrical transport behaviors of Cr 7 ͑Se 1−x Te x ͒ 8 compounds are investigated in detail. Spin-glass-like behavior is observed, which results from the spin frustration due to the competition between ferromagnetic and antiferromagnetic interactions. As Se is substituted by Te, a minimum of resistivity is observed in temperature dependence of resistivity and the temperature T min corresponding to the minimum increases with Te concentration. Hopping conductivity in terms of variable range-hopping is used to describe the electrical transport behavior below T min. The resistivity of these compounds is sensitive to the external magnetic field, which shifts the magnetic ordering temperature T MO to higher temperature and T min to lower temperature. The resistivity at the magnetic field becomes smaller, compared to the zero-field value, resulting in a negative magnetoresistance.