Magnetic and microwave absorption properties of BaFe12−x (Mn0.5Cu0.5Zr)x/2O19 synthesized by sol–gel processing
Introduction
The increase in electromagnetic pollution due to the rapid development of gigahertz (GHz) electronic systems and telecommunications has resulted in a growing and intense interest in electromagnetic-absorber technology. Electromagnetic interference (EMI) can cause severe interruption of electronically controlled systems. It can cause device malfunctions, generate false images, increase clutter on radar and reduce performance because of system-to-system coupling. Recent developments in microwave absorber technology have resulted in materials that can effectively reduce the reflection of electromagnetic signals on the one hand, and have good physical performance and lower production cost on the other [1], [2]. As far as thickness and working frequency bandwidth are concerned, magnetic composites have obvious advantages. The magnetic fillers often used in such composites are ferrite materials, such as spinel ferrites and hexaferrites [3], [4]. As compared to the usual spinel ferrites, the hexaferrites with planar magnetic anisotropy are of great interest for use as electromagnetic energy dissipation in the GHz range. Barium ferrite powders are ideal fillers for the development of electromagnetic attenuation materials at microwave, due to their low cost, low density, high stability, large electrical resistivity and high microwave magnetic loss [5], [6], [7]. In our previous papers [8], [9], the microwave attenuation properties were studied for Mn–Cu—Ti-, Mn—Ti-, Mn—Co- and Ti–Co-doped barium ferrites. Here, we report on the relationship between magnetic properties and microstructure for BaFe12−x(Mn0.5Cu0.5Zr)x/2O19. The predicated absorption and reflection loss demonstrates that BaFe12−x(Mn0.5Cu0.5Zr)x/2O19 may be a good candidate for electromagnetic materials with low reflectivity at microwave frequency. Phase identification, microstructure and magnetic properties of the samples were examined.
Section snippets
Experimental
For selection of the composition and the stoichiometry of barium ferrite, M-type barium ferrites with different composition were prepared using a sol–gel method [10]. Three samples of hexagonal ferrite powder, namely, ferrite “A” of composition [BaFe11(Mn0.5Cu0.5Zr)1/2O19], ferrite “B” of composition [BaFe10(Mn0.5Cu0.5Zr)2/2O19] and ferrite “C” of composition [BaFe9(Mn0.5Cu0.5Zr)3/2O19], were synthesized. Powders with particle sizes between 1 and 4 μm were obtained. Composite specimens were
Microstructure characteristics
The X-ray diffraction (XRD) patterns for the calcined powders of BaFe12−x(Mn0.5Cu0.5Zr)x/2O19 M-type hexaferrite samples synthesized at 1100 °C are shown in Fig. 1. Peaks for the doped barium ferrite appear at the same position as for the undoped ferrite, but with different intensities. In the doped ferrite cases, the dopants of Mn+2, Cu+2 and Zr+4 seem to dissolve/rearrange in the hexagonal structure to fulfill the formation of single hexagonal phase.
The structural parameters are listed in
Conclusion
Mn, Cu and Zr substitutions greatly modified a magnetic properties and the microstructures of barium ferrites. Mn–Cu–Zr mixture was very effective in reducing Hc at a low level of substitution (x=1). The samples (x=2 and 3) with higher magnetic susceptibility, larger coercive force and larger hysteresis loop exhibit larger microwave-absorbing ability. Microwave absorbers for applications over 15 GHz, and with satisfactory reflection losses, could be obtained at a thickness of 1.8 mm by
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2021, Materials Science and Engineering: BCitation Excerpt :Thus, the demand of microwave absorbers to reduce such unwanted radiation is ever-increasing. Hexaferrites are known to be magneto-dielectric material [3] and can effectively work as microwave absorbing material [4–7]. An ideal microwave absorber is required to have low reflection loss, wide absorption bandwidth and small matching thickness.