Ferromagnetic behavior of carbon nanospheres encapsulating silver nanoparticles

We report on the structure and magnetic properties of a silver and carbon nanocomposite. The as-synthesized nanocomposite consists of a matte-black powder composed of Ag nanoparticles encapsulated in carbon nanospheres (~100.3em0exnm diameter) that are interconnected in necklace-like structures. Magnetic measurements of the Ag and C nanocomposite, in its powder form, showed weak ferromagnetic behavior up to at least room temperature with a coercive field of 3890.3em0exOe at 20.3em0exK and 1030.3em0exOe at 3000.3em0exK, from which we estimate magnetic ordering up to 4250.3em0exK. However, pressing the Ag-C powder samples into tablets suppressed the ferromagnetism; the pressed samples instead exhibited diamagnetic behavior. Chemical analysis with EDS and trace metal analysis with ICP-MS indicated that there are no magnetic contaminants in the sample. Therefore, we attribute the ferromagnetism to the carbon nanospheres and propose a model for the observed magnetism. We also measured a pronounced peak in the magnetization between 50 and 900.3em0exK that was completely suppressed when measurements were made upon cooling; we attribute this peak to a first-order spin reorientation.