Hybrid nanocomposites based on superparamagnetic and ferromagnetic particles: A comparison of their magnetic and dielectric properties

Nanocomposites of magnetic nanoparticles and polymer matrices combine the properties of their components, and as such are good examples of functional nanomaterials with excellent application potential. Against this background, experimental and theoretical studies of such composites are of great interest. In this study we aim to provide insight into the static and dynamic magnetic response, as well as the dielectric response, of magnetic nanocomposites subjected to external magnetic and electric fields. We directly compare the behavior of polyurethane films doped with superparamagnetic Fe₃O₄, and blocked ferromagnetic CoFe₂O₄ nanoparticles. While a reversible, Langevin magnetization curve is observed for Fe₃O₄@PU films, hysteretic magnetic behavior is found in case of CoFe₂O₄@PU films. The hysteresis observed for CoFe₂O₄ nanoparticles can be explained by interactions at the interface between particles and polymer matrix in conjunction with its ferromagnetic nature. The results of dielectric spectroscopy experiments revealed different effects of Fe₃O₄ and CoFe₂O₄ nanoparticles on polymer dynamics.