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

The barium ferrite BaTi_xFe_12-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 (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 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.