Materials Chemistry and Physics 124 (2010) 353–358 Contents lists available at ScienceDirect Materials Chemistry and Physics journal homepage: www.elsevier.com/locate/matchemphys Low temperature synthesis of Fe 3 O 4 micro-spheres and its microwave absorption properties Shibing Ni 1 , Xiaolei Sun, Xinghui Wang, Guo Zhou, Feng Yang, Junming Wang, Deyan He ∗ Department of Physics, Lanzhou University, Lanzhou 730000, China article info Article history: Received 6 October 2009 Received in revised form 12 June 2010 Accepted 19 June 2010 Keywords: Magnetic materials Chemical synthesis Magnetic properties Microwave absorption abstract Fe 3 O 4 micro-spheres were synthesized by a simple chemical method at 90 ◦ C. It was demonstrated that the final size and morphology of Fe 3 O 4 was significantly affected by the additive NaF. The as-synthesized products were characterized by field emission scanning electron microscopy (FE-SEM), X-ray diffraction (XRD), vibrating sample magnetometer (VSM), and vector network analysis. The complex permittivity and permeability of paraffin wax and Fe 3 O 4 with different Fe 3 O 4 volume fraction were measured to increase linearly with increasing volume fraction of Fe 3 O 4 . When the matching thickness is 4 mm, the calculated reflection loss reaches a maximum value of -45.2 dB at 4.67 GHz with 40% volume fraction of Fe 3 O 4 . © 2010 Elsevier B.V. All rights reserved. 1. Introduction During the past few years, there has been a growing and widespread interest in microwave-absorbing materials due to their military and civil applications such as stealth defense system [1,2], microwave interference protection [3], and microwave darkroom [4]. Magnetic absorption materials made by dispersing magnetic fillers in an insulating matrix continue to play an important role in the investigation and application of microwave absorption mate- rials [5]. As ferrites can avoid the skin effect at high frequency and make the electromagnetic wave enter effectively due to their high resistivity (10 8 –10 12  cm), they can attenuate electromag- netic wave efficiently. In addition, for its higher efficiency and lower cost than that of other materials, they have been among the most popular conventional magnetic fillers. However, for a long period of time, much attention about ferrites has been focused on researching microwave absorption properties of new types of fer- rites [6–9], little work has been done on researching microwave absorption properties of the basic ferrite (magnetite), though it is well known that size and morphology would have important effect on the microwave absorption properties [10,11]. We have reported hydrothermal synthesis of well-dispersed Fe 3 O 4 nanoparticles and their microwave absorption properties earlier [12]. When the matching thickness is 3 mm, the calculated reflection loss reaches a maximum value of -21.2 dB at 8.16 GHz with 30% volume fraction ∗ Corresponding author. Fax: +86 931 8913554. E-mail addresses: shibingni07@gmail.com (S. Ni), hedy@lzu.edu.cn (D. He). 1 College of Mechanical and Material Engineering, Three Gorges University, 8 Daxue Road, Yichang 443002, PR China. of Fe 3 O 4 . Further researches on improving microwave absorp- tion properties and developing simpler method to realize size and morphology controlled fabrication of Fe 3 O 4 have been underway in our laboratory. For the purpose of obtaining a wide region of microwave absorption, recently, we have reported designed syn- thesis of Fe 3 O 4 –carbon sphere composite and their microwave absorption properties [13]. A wide region of microwave absorption was achieved due to dual dielectric and magnetic losses. When the matching thickness is 4 mm, the calculated reflection loss of the sample with 70% volume fraction of Fe 3 O 4 –carbon sphere com- posite exhibits a broad microwave absorption ranging from 2.5 to 18 GHz. In this paper, the main object is to develop a simpler method to achieve size and morphology tuned fabrication of Fe 3 O 4 , to research its microwave absorption properties, to explore the rela- tion between microwave absorption properties and the size and morphology of Fe 3 O 4 . 2. Experimental All the chemicals were analytical grade and purchased from Shanghai Chemical Reagents. In a typical procedure, 10 mmol (NH4)2Fe(SO4)2·6H2O, 5 mmol hexam- ethylenetetramine, and 1 g NaF were dissolved in 50 ml distilled water. After stirring for 20 min, the homogeneous green solution was transferred into a 500 ml vitreous jar, distilled water was subsequently added to 80% of its capacity. The vitreous jar was placed in an oven, heated at 90 ◦ C for 10 h. The suspension was centrifuged sequentially with distilled water and ethanol both four times at 6000 rpm for 5 min, the resulting black precipitate finally was dried in an oven at 60 ◦ C for 24 h. The structures of the resulting products were characterized by X-ray powder diffraction (Rigaku RINT2400 with Cu K radiation). Field emission scanning elec- tron microscopy (FE-SEM S-4800, Hitachi) was employed for the morphology and size analysis. For magnetic measurement, the as-synthesized Fe3O4 was loaded in a capsule and impacted, the weight of Fe3O4 was obtained by measuring the weight 0254-0584/$ – see front matter © 2010 Elsevier B.V. All rights reserved. doi:10.1016/j.matchemphys.2010.06.046