A simple route to synthesize ZnFe2O4 hollow spheres and their magnetorheological characteristics

In this paper, a simple route to synthesize hollow spheres of ZnFe2O4 without the assistance of a template is reported. The crystal structure and morphology of these particles were characterized by x-ray diffraction (XRD), transmission electron microscopy (TEM), and field emission scanning electron microscopy (FE-SEM). It was found that the final products were hollow spheres with perfect morphology, and their size and the thickness of their shells decreased with the increase of urea precursor. Ferromagnetism was observed from the magnetic hysteresis loops of the ZnFe2O4 hollow spheres at room temperature. The possible formation mechanism of the hollow spheres is discussed. In addition, ZnFe2O4 magnetorheological (MR) fluids were prepared and then their MR effect was investigated on a rotational rheometer equipped with a magnetic field generator.