Polymorphous Fe/FexOy core-shell and urchin-like composites were synthesized via a facile oxidation process at relatively low temperatures (100-300 degrees C) in the absence of surfactants or an external magnetic field. The oxidation temperature plays a key role in determining the morphology, crystal size, and composition of the resulting products. The static magnetic and electromagnetic (EM) properties of Fe/FexOy composites are influenced by their morphology, crystal size, and composition. In this study, excellent soft magnetic properties and enhanced permeability were obtained from core-shell Fe/FexOy composites with low FexOy shell contents and low surface anisotropy. In contrast, high coercivity and dielectric performance were exhibited by urchin-like Fe/FexOy composites with high shape and surface anisotropy. This work provides insights into the absorption mechanism of urchin-like complex absorption materials. (C) 2011 Elsevier B.V. All rights reserved.