Microstructure and magnetic properties of graphite-coated Gd nanocapsules

Gd nanocapsules, which are stable in air with the protection of graphite shells, are prepared by a modified arc-discharge technique. A size-induced structural transformation from the hexagonal-close-packed (hcp) to the higher-symmetry face-centered-cubic structure is observed. The graphite-coated hcp-Gd nanocapsules display a blocked state below 35 K, superparamagnetism between 35 and 290 K, and typical paramagnetism above 290 K. The hcp-Gd nanocapsules have a magnetic-entropy change -Delta S(m) of 48.8 J kg(-1) K(-1) at 6 K for an applied-field change from 1 to 7 T.