Modified composition of barium ferrite to act as a microwave absorber in X-band frequencies
Introduction
With the advancement of electronic technologies, special attention has focused on the development of new microwave materials and their composites for applications in the field of shielding and stealth technology. Therefore, demands to develop thinner electromagnetic (EM) wave absorbers with wider absorbing band-widths are ever increasing [1], [2]. EM wave energy can be completely absorbed and dissipated into heat through magnetic losses and dielectric losses if the characteristic impedance of free space is matched with the input characteristic impedance of an absorber. The microwave absorber can be used to minimize the electromagnetic reflection from metal plates such as aircraft, ships, tanks and walls of anechoic chambers and electronic equipment [3], [4]. For the purpose of preparing a low-reflecting absorber in the desired frequency range, two fundamental conditions must be satisfied; the first is that the incident wave can enter the absorber by the greatest extent (impedance matching characteristic), and the second is that the electromagnetic wave entering into the materials can be almost entirely attenuated and absorbed within the finite thickness of the absorber (attenuation characteristic). Among the materials used in microwave absorbing applications, ferrites exhibit an interesting behaviour. Ferrites have been used as absorbing materials in various forms, e.g. sheets, paints, films, ceramic tiles and powders loaded in matrix composites or mixed with conducting materials [5]. The hexagonal ferrites like barium ferrite are suitable as a radar absorbing material (RAM) due to their large values of permeability and magnetization as well as their good dielectric properties at microwave frequencies. X-band frequency radar has been of great interest to the military sector because it allows for high resolution imaging and greater precision target identification. There are different EM wave absorber materials being used, including ferrites, conducting fibers, ferromagnets, and carbon nanotubes [6], [7], [8]. Substitution for the Fe3+ and Ba2+ is an effective method to vary the magnetic properties of barium ferrite. After the Fe or Ba ions are substituted with Co–Ti, Zn–Ti, Zn–Sn, Co–Sn, Ni–Zr and Co–Mo [9], [10], [11], [12], [13], [14], the saturation magnetization, coercivity, anisotropy constant and ferromagnetic resonant frequency of barium ferrite are changed. The electromagnetic wave absorption by a particular material is limited to a narrow band of frequencies. This is one of the serious constraints in an absorbing material. If several kinds of barium ferrite with different resonant frequencies are combined into a multilayer structure, the material may absorb electromagnetic waves in a wide microwave band. The relationship between the ferromagnetic resonant frequency of the barium ferrite and the substitution elements requires further research. It is well known that some special phenomena possibly appear during ferromagnetic resonance at high frequency, such as multipeaks [15], [16]. A multipeak may increase the microwave absorption capability of barium ferrite. In the work carried out by Kagotani [17], after Fe and Ba ions were substituted with La, Zn and Mn ions, the microwave absorption peaks of barium ferrite varied gradually in the range of frequency from 4 to 16 GHz. Moreover, no secondary peak of the ferromagnetic resonance arose. When Meshram [18] substituted Fe ions with Co, Ti and Mn ions, the microwave absorption properties of barium ferrite were improved. But several peaks appeared on the absorption spectra. The factors resulting in the multipeak have been researched for a long time. They are related with not only the high frequency, but also the grain size, crystalline structure and magnetic domains [15]. In this paper, the magnetic and microwave absorption properties and the ferromagnetic resonant frequencies of Co–Mn–Ti substituted barium ferrites are explored. The factors resulting in the multipeak during ferromagnetic resonance are also discussed.
Section snippets
Experimental
Polycrystalline samples of substituted barium ferrite with the stoichiometric formula BaCoxMnxTi2xFe12−4xO4 () were prepared by a conventional ceramic technique. The starting materials were AR grade BaCO3, Fe2O3, CoO2, MnO2, and TiO2. Appropriate amounts of these precursors were taken and ground/mixed thoroughly. The resultant mixtures were dried and calcined at 1000 ∘C for 8 h. The powder was further ground and pressed in the form of pellets using a small amount of PVA as binder with an
Phase analysis and SEM morphology
The X-ray diffraction patterns of the samples BaCoxMnxTi2xFe12−4xO4 with , 0.10, 0.20, 0.30, 0.40, 0.50) are shown in Fig. 1, which represent the typical M-type hexagonal structure. The peaks of the doped barium ferrites appear at the same position as for the undoped ferrite. In the doped ferrite cases, the dopants of Mn2+, Co2+ and Ti4+ seem to be rearranged in the hexagonal structure to fulfil the formation of a single phase of hexagonal ferrite.
SEM microstructure images of the eroded
Conclusions
BaCoxMnxTi2xFe12−4xO19 hexaferrites were prepared by solid-state reaction. Mn, Co and Ti substitutions significantly modified the magnetic shielding properties and the microstructures of the barium ferrites. This composition has been very effective in reducing due to microstructure and anisotropy variation. It is observed that the magnetization decreases slowly with increase in the Co, Mn and Ti concentration in BaCoxMnxTi2xFe12−4xO4. This compound, even with small thickness, exhibits a very
Acknowledgements
The authors are grateful to Director, National Physical Laboratory, New Delhi for providing constant encouragement and motivation to carry out this work. The authors are grateful to Dr. S.K. Dhawan and K.N. Sood, NPL New Delhi, for providing the facilities for EM absorption and SEM measurements.
References (21)
- et al.
J. Magn. Magn. Mater.
(2004) - et al.
J. Magn. Magn. Mater.
(2006) - et al.
J. Magn. Magn. Mater.
(1994) - et al.
J. Magn. Magn. Mater.
(1998) - et al.
J. Magn. Magn. Mater.
(2004) - et al.
J. Magn. Magn. Mater.
(2004) - et al.
J. Magn. Magn. Mater.
(2006) - et al.
J. Magn. Magn. Mater.
(2009) - et al.
Mater. Res. Bull.
(2008) - et al.
IEEE Trans. Magn.
(1999)
Cited by (101)
Effect of Ce doping on electromagnetic characteristics and absorbing properties of M-type barium ferrite
2024, Materials Today CommunicationsEffect of La<sup>3+</sup>and Al<sup>3+</sup> doping on the crystal structure and magnetic properties of strontium hexaferrites
2024, Journal of Alloys and CompoundsImprovement in the structural, magnetic and electromagnetic behaviour of barium hexaferrites with yttrium doping for EMI shielding
2024, Journal of Alloys and CompoundsSynthesis and characterization of BFO/BTO/ZnO nanocomposites for promising EMI shielding applications
2023, Inorganic Chemistry CommunicationsInvestigations on structural, Mossbauer, dielectric, and ferroelectric properties of La doped barium hexaferrite
2023, Physica B: Condensed MatterTailoring tactics for optimizing microwave absorbing behaviors in ferrite materials
2023, Materials Today Physics