Synthesis and magnetic properties of polymer nanocomposites with embedded iron nanoparticles

Magnetic nanoparticles embedded in polymer matrices have excellent potential for electromagnetic device applications like electromagnetic interference suppression. We have synthesized polymer nanocomposites of poly(methylmethacrylate) doped with varying concentrations of iron nanoparticles (∼20 nm in size). The iron nanoparticles were produced using a microwave plasma technique and have a natural oxide surface layer for passivation. These nanocomposites were processed using melt blending technique. The polymer processing conditions were optimized to achieve good uniform dispersion of the nanoparticles in the polymer matrix. The concentration and dispersion of nanoparticles were varied in a controlled way. Surface characterization with scanning electron microscopy indicates that, to a large extent, the iron nanoparticles are embedded in the bulk; the surface mainly showed features associated with the polymer surface. Static magnetic properties such as susceptibility and $\mathrm{M–H}$ loops were studied using a physical property measurement system. The variation of the ferromagnetic response was consistent with the varying volume concentration of the nanoparticles, the polymer itself contributing a diamagnetic response. At room temperature, hysteresis loops exhibited a somewhat large coercivity (260 Oe) associated with a surface oxide layer on the particles. Overall, the excellent dispersion coupled with reasonable control over magnetic properties achieved in our experiments is promising for electromagnetic applications of these materials.