Preparation and properties of dysprosium nanocapsules coated with boron, carbon, and dysprosium oxide

Boron-coated dysprosium/dysprosium oxide, carbon-coated dysprosium/DyC2, and dysprosium oxide-coated dysprosium nanocapsules were prepared using an arc discharge method in diborane, methane, and argon, respectively. The magnetization of these nanocapsules has been measured at temperatures between 4 and 290 K, in applied fields up to 6 T. The transition temperature of nanocrystalline Dy from the helical phase to the ferromagnetic phase is much lower than that of bulk Dy. The linear temperature dependence of the inverse susceptibility of these nanocapsules, being a mixture of superparamagnetic Dy and paramagnetic dysprosium oxide or carbide, can be explained within the molecular field theory with magnetic moments with the total angular momentum J=15/2 and the Landé factor g=4/3. We discuss the relations between the structure and the magnetization of these nanocapsules.