Magnetic and microwave absorption properties of BaFe12−x (Mn0.5Cu0.5Zr)x/2O19 synthesized by sol–gel processing

doi:10.1016/j.jmmm.2007.02.043

Journal of Magnetism and Magnetic Materials

Volume 316, Issue 2, September 2007, Pages e105-e108

https://doi.org/10.1016/j.jmmm.2007.02.043 Get rights and content

Abstract

BaFe₁₂₋_x (Mn_0.5Cu_0.5Zr)_x_/2O₁₉ hexaferrites with x=1, 2 and 3 were prepared by sol–gel process. The ferrite powders possess hexagonal shape and are well separated from one another. The powders of these ferrites were mixed with polyvinylchloride (PVC) plasticizer to be converted into a microwave absorbing composite ferrite with a thickness of 1.8 mm. X-ray diffractometer (XRD), scanning electron microscope (SEM), ac susceptometer, vibrating sample magnetometer and vector network analyzer were used to analyze its structure, electromagnetic and microwave absorption properties. The results showed that magnetoplumbite structures for all samples were formed. The sample with higher magnetic susceptibility and coercivity exhibits a larger microwave absorbing ability. Also the present investigation demonstrates that a microwave absorber using BaFe₁₂₋_x(Mn_0.5Cu_0.5Zr)_x_/2O₁₉ (x=2 and 3)/PVC with a matching thickness of 1.8 mm can be fabricated for applications over 15 GHz, with reflection loss more than −25 dB for specific frequencies, by controlling the molar ratio of the substituted ions.

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(Mn_0.5Cu_0.5Zr)_x_/2O₁₉. The predicated absorption and reflection loss demonstrates that BaFe₁₂₋_x(Mn_0.5Cu_0.5Zr)_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(Mn_0.5Cu_0.5Zr)_1/2O₁₉], ferrite “B” of composition [BaFe₁₀(Mn_0.5Cu_0.5Zr)_2/2O₁₉] and ferrite “C” of composition [BaFe₉(Mn_0.5Cu_0.5Zr)_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(Mn_0.5Cu_0.5Zr)_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 H_c 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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Magnetic and microwave absorption properties of BaFe12−x (Mn0.5Cu0.5Zr)x/2O19 synthesized by sol–gel processing

Abstract

Introduction

Section snippets

Experimental

Microstructure characteristics

Conclusion

Composites Part A

Composites Part A

J. Magn. Magn. Mater.

J. Appl. Phys.

IEEE Trans. Electromagn. Comat.

J. Appl. Phys.

Magnetic and microwave absorption properties of BaFe₁₂₋_x (Mn_0.5Cu_0.5Zr)_x_/2O₁₉ synthesized by sol–gel processing