Morphology dependence of static magnetic and microwave electromagnetic characteristics of polymorphic Fe 3 O 4 nanomater
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Jianguo Guan State Key Laboratory of Advanced Technology for Materials Synthesis and Processing, Wuhan University of Technology, Wuhan 430070, People’s Republic of China
Haisheng Qian Zhejiang Key Laboratory for Reactive Chemistry on Solid Surface, College of Chemistry and Life Sciences, Zhejiang Normal University, Jinhu 321004, People’s Republic of China (Received 11 January 2011; accepted 11 April 2011)
In the present work, Fe3O4 nanospheres, sponges, and urchins were prepared. Investigation of static magnetic and microwave electromagnetic (EM) characteristics of polymorphic Fe3O4 nanomaterials showed that morphology plays a crucial role in determining the resulting properties. Compared with Fe3O4 nanospheres and urchins, enhanced saturation magnetization and coercivity were observed in Fe3O4 sponges composed of ordered nanofibers. Enhancement of saturation magnetization and coercivity are associated with increased magnetic interactions and shape anisotropy, respectively. The Fe3O4 sponges and urchins produced reflection loss (RL) values of 35.77 dB at 8.0 GHz and 43.23 dB at 16.8 GHz, respectively. The excellent microwave absorption performance is ascribed to their unique morphologies. Such morphologies resulted in reinforced EM parameters and multiresonant behavior.
I. INTRODUCTION
New types of nanostructured materials, such as nanoflowers, urchin-like structures, dendritic structures, and multipods, have recently attracted considerable attention as microwave-absorbing and shielding materials.1–6 This is because of the ability of these complex nanostructures to maintain the basic features of the original material and confer novel absorbing properties and mechanisms. More importantly, their high Brunauer–Emmett–Teller (BET) specific surface area (SBET) and adjustable shape parameters allow control of subsequent microwave electromagnetic (EM) and absorbing characteristics. In particular, Fe3O4 nanomaterials have aroused much interest because of their potential applications as catalysts, gas sensors, magnetic filters, electrode materials, magnetic storage media, and as materials for spin electronics and biomedical research.7–10 Fe3O4 complex nanostructures could also be utilized as microwave absorbing materials.11–13 However, studies on microwave absorption properties of Fe3O4 nanomaterials are few. Chen et al.11 found that porous Fe3O4/SnO2 core/shell nanorods exhibited dual-frequency absorption characteristics, with a)
Address all correspondence to this author. e-mail: [email protected] DOI: 10.1557/jmr.2011.131 J. Mater. Res., Vol. 26, No. 13, Jul 14, 2011
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a maximum reflection loss of 27.38 dB at 16.72 GHz on a thickness of 4 mm. Fu and coworkers12 reported that flower-like ZnO/Fe3O4 nanocomposites showed markedly high EM wave absorption compared with the individual nanostructures (bare flower-like tubular ZnO or Fe3O4 nanoparticles). This difference was ascribed to the threedimensional conductive networks of the nanocomposites and the diffuse reflections produ
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