GHz range electromagnetic wave absorption properties of M and W-type two phase hexaferrite

The electromagnetic wave absorption properties of BaZn_2xFe_10.8+4x(Sn_0.5 Mn_0.5)_1.2O_19+8x (x = 0.25 to approximately 0.75) sintered bodies, consisting of BaM and BaZn₂W-type hexaferrite phases, were studied. The relative complex permittivity values hardly changed, with respect to composition (x). In the frequency dispersion of the relative complex permeability of some of the samples, two peaks were observed at frequencies centred around 14 and 17 GHz. The intensities of these permeability peaks at 14 and 17 GHz, increased and decreased with increasing x, respectively. The Reflection Loss (R.L.) was less than -20 dB, and almost the same matching thickness (d_m) was obtained in all of the samples. However, the bandwidth for R.L.≤-20 dB (ΔF) was affected by changes in composition (x), and the BaZnFe_12.8(Sn_0.5Mn_0.5)_1.2O₂₃ sample sintered at 1473 K for 10 h in air, exhibited a maximum value of ΔF = 2.2 GHz, with a relatively small matching thickness of d_m = 1.0 mm. When compared with a BaM-type single phase sintered body (BaFe₉(Ti_0.5Mn_0.5)₃O₁₉, d_m = 0.6 mm, ΔF = 0.1 GHz), the d_m was slightly larger but ΔF became wider. It is concluded that using a two-phase microstructure composed of M and W-type hexaferrite, is an effective method of expanding ΔF.