Tailoring electromagnetic wave absorption properties of M-type barium ferrite through Nd3+–(Nb5+/Ta5+) cosubstitution

M-type barium ferrites (Ba 1−x Nd x Fe 12−x M x O 19 , x = 0–0.3) with Nd 3+ –M 5+ (M = Nb 5+ and Ta 5+ ) ions substituting Ba 2+ and Fe 3+ ions were prepared via a solid-state reaction. The crystalline phases, microstructure, magnetic properties , and electromagnetic wave absorption of the ion-substituted M-type barium ferrites were investigated. The saturation magnetization strength and coercivity changed with increasing substitution ratio x. The substitution of Nd–Nb and Nd–Ta ions reduced the anisotropic field of the material, thus lowering the natural resonant frequency. The complex permittivity of the ion-substituted samples was enhanced compared with that of the unsubstituted samples. Interfacial polarization, dipole polarization and dipole relaxation were induced by the substituted ions. The multiple natural resonances contributed by the numerous g-factors generated by Fe 3+ ions and the exchange coupling among Fe 3+ , Fe 2+ , and O 2− ions controlled the permeability of M-type barium ferrite, which broadened the effective absorption bandwidth. The excellent complex permittivity and complex permeability enabled the substituted samples to attain high attenuation constants and better impedance-matching properties. Hence, a strong reflection loss of (−35)–(−50) dB, an ultrabroad bandwidth of ∼13.5 GHz, and a low matching thickness of < 0.75 mm were obtained in the frequency range of 26.5–40 GHz. The electromagnetic wave absorption was also improved in the frequency range of 2–18 GHz, where the samples with the substitution ratio of x = 0.1 exhibited relatively good performance with small matching thickness (<1.5 mm). Thereby, Nd–Nb and Nd–Ta substituted M-type barium ferrites are prospective candidates that can be used as an excellent microwave absorber material in the centimeter and millimeter wavelength frequency range.