Magnetic stability of Al2O3-coated fcc-Co nanocapsules

Al2O3-coated fcc-Co nanocapsules have been fabricated by arc-discharge. The saturation magnetization at 295 K of the nanocapsules is 41.79 emu/g, which is much higher than that of Co nanoparticles embedded in Al2O3 matrix. The saturation magnetization is almost unchanged after being annealed at 400 K for 2 h in air or being exposed in air for at least 300 days, which indicates that the magnetic properties of the present nanocapsules are very stable. The nanocapsules have a nano-onion structure: the shells from the exterior to the interior are amorphous Al2O3 and Al, and the innermost core is fcc-Co. When the nanocapsules are annealed at 400 K for 2 h, the nanocapsules have a core/shell structure with the core of fcc-Co and the shell of amorphous Al2O3.