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

Abstract

The barium ferrite BaTi _x Fe _{12− x} O ₁₉ ( x = 0.2, 0.4, 0.6, 0.8) (BFTO- x) ceramics doped by Ti ⁴⁺ 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 ( M _s) decreases gradually but the change trend of coercivity ( H _c) is complex under the synergy of the changed grain size and the magnetic crystal anisotropy field. Relying on the high valence of Ti ⁴⁺, 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.