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 ($\sim 10\mathrm{nm}$ 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 $389\mathrm{Oe}$ at $2\mathrm{K}$ and $103\mathrm{Oe}$ at $300\mathrm{K}$, from which we estimate magnetic ordering up to $425\mathrm{K}$. However, pressing the $\mathrm{Ag}\text{−}\mathrm{C}$ 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 $90\mathrm{K}$ that was completely suppressed when measurements were made upon cooling; we attribute this peak to a first-order spin reorientation.

• Received 10 January 2006

DOI:https://doi.org/10.1103/PhysRevB.74.214418