Superparamagnetic FeCo and FeNi Nanocomposites Dispersed in Submicrometer-Sized C Spheres

Magnetic spheres with average diameter 100 nm, consisting of FeCo and FeNi nanomagnets (with average diameters 5.9 +/- 1 and 4.6 +/- 0.3 nm, respectively) dispersed in spherical carbon colloid have been synthesized using the radio frequency plasma-enhanced chemical vapor deposition technique. The nanoparticles are tightly embedded in the C matrix and well protected from oxidation. Superparamagnetic features such as typical Langevin-like magnetization curves are observed for the nanocomposites. A comprehensive analysis of the presence of dipolar interactions has been carried out within the framework of the mean-field model. The size of the nanoparticles constituting the carbon spheres is near to the optimal value where Neel losses are maximal and considerable Neel-type specific absorption rates are observed. The material may hence provide a new material based approach to realize biocompatibly protected superparamagnetic beads for application in biological environments, in particular, for magnetic hyperthermia.