Complex permittivity, permeability, magnetic and microwave absorbing properties of Bi3+ substituted U-type hexaferrite

Bi3+ substituted polycrystalline samples of Barium U-type hexaferrite, (Ba1-3xBi2x)4Co2Fe36O60 (0.05 ≤ x ≤ 0.15, in steps of 0.05), were prepared through solid state reaction route. The effect of Bi3+ substitution on the structural properties of Barium hexaferrrite samples was investigated through X-ray diffraction (XRD) studies. Le Bail refinement of XRD patterns confirmed the formation of desired U-type hexaferrite phase in all the prepared samples. The room temperature magnetic hysteresis (M-H) loops shows that the saturation magnetization (Ms) initially increases to 63.5 emu/g for x = 0.10 sample and then reduces to 55.3 emu/g for x = 0.15 sample. Nicholson-Ross-Weir (NRW) algorithm has been employed to calculate the complex permittivity (ε∗=ε′-iε″) and permeability (μ∗=μ′-iμ″) spectra in 2-18 GHz frequency range. The reflection loss (RL) was calculated from the complex permittivity (ε∗) and permeability (μ∗) spectra using transmission line theory. The minimum reflection loss (RLmin) of −35.5 dB (MW absorption of 99.97%) was obtained for (Ba0.55Bi0.30)4Co2Fe36O60 sample at 10.6 GHz MW frequency. Moreover, the broad frequency bandwidth of 8.4 GHz (over X- and Ku-band), for the reflection loss of −10 dB (90% MW absorption) or less, was attained in (Ba0.55Bi0.30)4Co2Fe36O60 sample.