Electromagnetic and microwave absorbing properties of W-type barium ferrite doped with Gd³⁺

W-type barium ferrites doped with Gd³⁺, Ba_1-x Gd _x (Zn_0.3Co_0.7)₂Fe₁₆O ₂₇ (x = 0, 0.05, 0.10, 0.15, 0.20), were prepared by a sol-gel method. The effects of Gd³⁺ substitution on their microstructure, electromagnetic properties and microwave absorptive behavior were analyzed. The XRD patterns showed the single phase of W-type barium ferrite when x ≤ 0.15. Microwave electromagnetic properties of samples were studied at the frequency range from 2 GHz to 18 GHz using a network analyzer (Agilent 8722ET). The complex permittivity ε (δ′, ?″) increased gradually when x ≤ 0.10, but it decreased as x = 0.15. The real permeability (μ′) decreased with the increase of Gd³⁺ content, while the imaginary permeability (μ″) increased when x ≤ 0.10. All these reasons were discussed using the electromagnetic theory. Furthermore, the ferrite-epoxy compound coating materials with 80 wt.% of Ba_0.9Gd _0.1(Zn_0.3Co_0.7)₂Fe ₁₆O₂₇ were prepared to measure the microwave absorbing properties. The maximum of reflection loss (RL) reached about -27 dB and RL was below -10 dB in the frequency range of 8-18 GHz when the thickness was 1.92 mm.