Preparation and ferromagnetic properties of Ni0.5Zn0.5Fe2O4/polyaniline core–shell nanocomposites

Magnetic Ni_0.5Zn_0.5Fe₂O₄‐crosslinked polyaniline composites with a core–shell structure were prepared in the presence of Ni_0.5Zn_0.5Fe₂O₄ magnetic powder in a toluene solution containing iron chloride as a surfactant and dopant. Structural characterization by Fourier transform infrared, X‐ray diffraction, scanning electron microscopy, and transmission electron microscopy proved that Ni_0.5Zn_0.5Fe₂O₄ in the composites was responsible for the ferromagnetic behavior of the composites. The effects of the polyaniline and temperature on the magnetic properties of the Ni_0.5Zn_0.5Fe₂O₄/polyaniline composites were studied with electron paramagnetic resonance and superconducting quantum interference device techniques. A clear evolution from ferromagnetic resonance to electron paramagnetic resonance was observed as a function of temperature, which was related to the passage through the Curie point (～420 K). The magnetic properties of the resulting composites showed ferromagnetic behavior, such as high‐saturated magnetization (saturation magnetization = 35–39 emu/g), low coercive force (coercivity = 22–28 G), and low blocking temperatures (～23 K). © 2006 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 44: 2657–2664, 2006