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Abstract: Carbon-encapsulated Fe nanoparticles have been successfully synthesized by a two-step procedure method of hydrothermal and subsequent thermal reduction process. The introduction of hydrogen atmosphere helps to obtain pure α-Fe phase and the lower annealing temperature (at 550°C). The morphological characterization indicates that the nanoparticle presents a quasi-spherical shaped, core–shell structure with diameter ranged from 10 to 20nm and a carbon shell of about 4nm. The results of X-ray diffraction and Raman spectrum demonstrate that carbon in the as-synthesized product is in amorphous phase. Magnetic measurements reveal the ferromagnetic behavior of the product. [Copyright &y& Elsevier]

Abstract: Morphology, crystal structure, magnetic and microwave absorption properties of BaTiO3-based ferromagnetic/ferroelectric composites were investigated in this research. It was evident that Niph name="sbnd" />P/BaTiO3 composite was a narrowband absorber, whereas carbonyl iron/BaTiO3 composite samples showed broadband absorption characteristics. For the carbonyl iron/BaTiO3 composite, a reflection loss exceeding −20dB was obtained in the frequency range of 3.8–5.8GHz with an absorber thickness of 2.3–3.3mm. An optimal RL of −46dB was found at 4.7GHz for an absorber thickness of 2.8mm. The effective absorption bandwidth with RL<−10dB was extended and reached 16GHz (2–18GHz). Moreover, the intrinsic reasons for microwave absorption of the composites, the dielectric loss and magnetic loss mechanics were also investigated. [Copyright &y& Elsevier]

Abstract: The flower-like ZnO and ZnO/carbonyl-iron composite have been prepared by a sonochemical route and ball-milling process, respectively. For ZnO/carbonyl-iron composite, a reflection loss (RL) exceeding −20dB was obtained in a broad frequency range of 8.4–17.9GHz with a thin thickness of 1.2–2.3mm. An optimal RL of −61dB was found at 11.7GHz for an absorber thickness of 1.91mm. It is demonstrated that the attractive microwave-absorption properties are a consequence of a proper electro-magnetic impedance match and geometrical cancellation at the air–material interface. In addition, an impedance mismatch function was proposed, which provides an effective method to determine the microwave absorbing properties from the intrinsic materials constants. The calculated value of matching frequency and thickness is well consistent with the experimental data. The method also provides a simple theoretical graphic aid for determining the absorption characteristics and the location of the matching conditions in the frequency domain. [Copyright &y& Elsevier]