A neutron diffraction investigation of high valent doped barium ferrite with wideband tunable microwave absorption

Abstract

The barium ferrite BaTixFe12−xO19 (x = 0.2, 0.4, 0.6, 0.8) (BFTO-x) ceramics doped by Ti4+ were synthesized by a modified sol—gel method. The crystal structure and magnetic structure of the samples were determined by neutron diffraction, and confirm that the BFTO-x ceramics were high quality single phase with sheet microstructure. With x increasing from 0.2 to 0.8, the saturation magnetization (Ms) decreases gradually but the change trend of coercivity (Hc) is complex under the synergy of the changed grain size and the magnetic crystal anisotropy field. Relying on the high valence of Ti4+, double resonance peaks are obtained in the curves of the imaginary part of magnetic conductivity (μ″) and the resonance peaks could move toward the low frequency with the increase of x, which facilitate the samples perform an excellent wideband modulation microwave absorption property. In the x = 0.2 sample, the maximum reflection loss (RL) can reach −44.9 dB at the thickness of only 1.8 mm, and the bandwidth could reach 5.28 GHz at 2 mm when RL is less than −10 dB. All the BFTO-x ceramics show excellent frequency modulation ability varying from 18 (x = 0.8) to 4 GHz (x = 0.4), which covers 81% of the investigated frequency in microwave absorption field. This work not only implements the tunable of electromagnetic parameters but also broadens the application of high-performance microwave absorption devices.

Construction of plate‐like magnetic heterostructure for synergistic microwave absorption

“…Unlike the bulk magnetic materials that possess natural resonant frequencies ($${f}_r$$) at megahertz frequencies, the $${f}_r$$ of plate materials is shifted to the gigahertz range. According to the equation $${f}_r = \gamma {H}_a/2\pi \ $$, where γ is the anisotropy ratio and $${H}_a$$ is the anisotropy field, the resonant frequency can be adjusted by changing the anisotropy field of the material, which is related to the size and morphology of the material 41,42 . The $$\mu ^{\prime\prime}$$ curves of all samples exhibit multiple peaks in the low‐frequency region, indicating that the plate material obtained from the nitridation of NiFe‐LDH can break Snoek's limit 19 .…”

“…According to the equation 𝑓 𝑟 = 𝛾𝐻 𝑎 ∕2𝜋 , where 𝛾 is the anisotropy ratio and 𝐻 𝑎 is the anisotropy field, the resonant frequency can be adjusted by changing the anisotropy field of the material, which is related to the size and morphology of the material. 41,42 The 𝜇 ′′ curves of all samples exhibit multiple peaks in the low-frequency region, indicating that the plate material obtained from the nitridation of NiFe-LDH can break Snoek's limit. 19 While ONA380 combines magnetic oxides, magnetic nitrides, and magnetic alloys in a twodimensional space, on one hand, the plate material is beneficial to breaking the Snoek's limit and, on the other hand, is beneficial to building magnetic coupling networks to enhance the synergistic effect of heterogeneous magnetic interfaces.…”

“…Among the various ferrites, spinel ferrite has the most attractive microwave absorption (MA) performance due to the high magnetic loss at megahertz frequencies 11–13 . However, the rapidly decreased permeability of magnetic materials at gigahertz, known as the Snoek's limit, has greatly limited the performance of ferrite‐based MAMs 14–16,46,47 …”

“…[11][12][13] However, the rapidly decreased permeability of magnetic materials at gigahertz, known as the Snoek's limit, has greatly limited the performance of ferrite-based MAMs. [14][15][16]46,47 Therefore, the ferrites are usually incorporated with other nonmagnetic materials to compensate for the deceased permeability and attenuation ability at high frequency. For instance, Shen et al designed FeNi/NiFe 2 O 4 /NiO/C nanofibers with the RL min of −40.9 dB at 4.5 GHz.…”

Determining the Actual Composition of Nb5+–Ni2+ Codoped Barium Ferrites to Controllably Regulate the Microwave Absorbing Properties

“…M-type barium ferrite BaFe 12 O 19 (BFO), one kind of a typical ferrite material, has been versatilely used as permanent magnet materials, magnetic recording materials, etc. , More notably, it is also one of the highest potential microwave absorbers because of its large magnetic loss from natural resonance. − The foreign ion doping has been a very common and mature strategy to modify the electronic structure and magnetic characteristics. − In our previous work, we also have proposed tetravalent or pentavalent ions such as Zr 4+ , Ti 4+ , and Nb 5+ ions to substitute Fe 3+ ions of M-type barium ferrite. As a result, the Fe 2+ concentration is increased to keep the charge balance, and thus enhanced exchange coupling among Fe 2+ , Fe 3+ , O – ions is achieved in barium ferrites, which leads to multiresonant permeability and finally contributes multiple RL peaks for broadening the bandwidth effectively to ∼12 GHz. − However, the narrow adjustable frequency range of the RL peaks restricts its wide application.…”