Magnetic properties of dendrimer-encapsulated iron nanoparticles containing an average of 55 and 147 atoms

The synthesis, characterization and magnetic properties of Fe nanoparticles containing an average of 55 and 147 atoms are described. The nanoparticles are prepared using dendrimer templates, and therefore they are nearly size-monodisperse. In the absence of oxygen and water, the Fe nanoparticles are stable, but they decompose quickly when exposed to air. Magnetic analysis indicates that the 55-atom nanoparticles are superparamagnetic, but the 147-atom materials undergo a transition to ferromagnetic at 6 K. Both materials exhibit suppression of the magnetic saturation compared to bulk Fe.