Magnetic Ni0.5Zn0.5Fe2O4-Crosslinked polyaniline composites with a core-shell structure were prepared in the presence of Ni0.5Zn0.5Fe2O4 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 Ni0.5Zn0.5Fe2O4 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 Ni0.5Zn0.5Fe2O4/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 (similar to 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 (similar to 23 K). (c) 2006 Wiley Periodicals, Inc.