Morphology and Magnetic Properties of Hollow Co3O4 Spheres

Nanostructured hollow Co3O4 spheres are synthesized by ultrasonic spray pyrolysis. Nanocrystals forming the sphere structure have different sizes and packing density, depending on the synthesis conditions. The samples are studied by X-ray diffraction, scanning electron microscopy, low-temperature nitrogen adsorption, vacuum pycnometry, and Raman and X-ray photoelectron spectroscopies. The field and temperature dependences of magnetization show that the magnetic properties and the Neel temperature of Co3O4 hollow spheres are determined by the size and packing density of nanocrystals.