Exchange coupling controlled ferrite with dual magnetic resonance and broad frequency bandwidth in microwave absorption

Abstract

Ti-doped barium ferrite powders BaFe12−xTixO19 (x = 0, 0.2, 0.3, 0.4, 0.5, 0.6, 0.7 and 0.8) were synthesized by the sol–gel method. The phase structure and morphology were analyzed by x-ray diffraction (XRD) and scanning electron microscopy, respectively. The powders were also studied for their magnetic properties and microwave absorption. Results show that the Ti-doped barium ferrites (BFTO) exist in single phase and exhibit hexagonal plate-like structure. The anisotropy field Ha of the BFTO decreases almost linearly with the increase in Ti concentration, which leads to a shift of the natural resonance peak toward low frequency. Two natural resonance peaks appear, which can be assigned to the double values of the Landé factor g that are found to be ∼2.0 and ∼2.3 in the system and can be essentially attributed to the existence of Fe3+ ions and the exchange coupling effect between Fe3+ and Fe2+ ions, respectively. Such a dual resonance effect contributes a broad magnetic loss peak and thus a high attenuation constant, and leads to a dual reflection loss (RL) peak over the frequency range between 26.5 and 40 GHz. The high attenuation constants are between 350 and 500 at peak position. The optimal RL reaches around −45 dB and the practicable frequency bandwidth is beyond 11 GHz. This suggests that the BFTO powders could be used as microwave absorbing materials with extraordinary properties.

Multi-susceptibile Single-Phased Ceramics with Both Considerable Magnetic and Dielectric Properties by Selectively Doping

“…4, in which there are two resonance peaks with two Landé factors ( g ) of 2.0 and 2.3 appearing in imaginary part ( μ ″, the magnetic loss) of the relative complex permeability of BaFe 12-x Ti x O 19 (x = 0.5, 0.6, 0.7 and 0.8) over 26.5–40 GHz10. As a matter of fact, the g of around 2.3 is from the exchange coupling between Fe 3+ and Fe 2+ ions (Fe 3+ /Fe 2+ pairs) which is different from ~2.0 of Fe 3+ in the ferrites10. The intensity of the peak about Fe 3+ /Fe 2+ pairs increases apparently with increasing Ti 4+ ions.…”

“…Considering the high electrical resistivity of barium ferrite, eddy loss can be neglected10. Magnetic loss of BaFe 12-x Ti x O 19 over the frequency range between 1 MHz and 100 MHz is contributed dominantly by hysteresis loss and residual loss25.…”

“…Ti 4+ , Nb 5+ and Zr 4+ are universal doping ions with higher electron valence than that of Fe 3+ . In this case, Ti 4+ , Nb 5+ and Zr 4+ ions are found to replace Fe 3+ ions due to their close ionic radii and valance state, making part of neighbor Fe 3+ ions transfer into Fe 2+ ions for charge balance10. The electron hopping between Fe 3+ and Fe 2+ ions form electron pair dipoles(Fe 3+ /Fe 2+ pairs), which will cause colossal permittivity11.…”

Synthesis and excellent electromagnetic absorbing properties of copolymer (N-methylpyrrole-co-pyrrole) and Ba–Nd–Cr ferrite

“…Compared with the dielectric loss media, the magnetic loss media can be fabricated into the thin high-efficient EMW absorbents because of the high magnetic loss [7,8], among which the ferrite is an excellent EMW absorbent due to the advantages of the high permeability, strong magnetism, and easy preparation. Recently, several types of ferrites have been reported, such as spinel ferrite [9,10], Z-type [11,12], W-type [13,14], Y-type [15] and M-type magnetoplumbite [16,17]. Ba ferrite, among them, has been widely studied due to its strong magnetism and high electrical resistivity in the range of 10 6 -10 9 Hz [14,18,19].…”

“…Ba ferrite, among them, has been widely studied due to its strong magnetism and high electrical resistivity in the range of 10 6 -10 9 Hz [14,18,19]. For example, the W-type BaCoZnFe 16 O 27 shows a RL = À18 dB at 5.5 GHz [14]. The specific saturation magnetization of Ba-ferrite/a-Fe 2 O 3 microfibers can increase from 56.1 to 97.5 Am 2 kg À1 by changing the reduction temperature, and it presents the reflection loss (RL) < À10 dB in the range 7.9-15.4 GHz and the optimal RL = À20.6 dB [18].…”