Magnetic and microwave absorbing properties of Ti and Co substituted M-hexaferrites in Ka-band frequencies (26.5 ~ 40 GHz)

Magnetic and microwave absorbing properties of M-hexaferrites have been investigated in Ka-band frequencies (26.5 ~ 40 GHz) with substitution of Ti⁺⁴ and Co⁺² ions for Fe⁺³ sites. The powders of composition BaFe_12-2xTi_xCo_xO₁₉ were prepared by conventional ceramic processing, where the substitution ratio x was varied from 0.0 to 2.0. With the calcined powders, polycrystalline bulk and composite sheet samples were prepared for the evaluation of magnetic and microwave absorbing properties. VSM measurements indicate that the saturation magnetization and coercivity of the M-hexaferrites decrease with the substitution of Ti and Co, which is attributed to the reduction in crystal anisotropy field by changing of easy-axis of magnetization from c-axis to basal plane. Ferromagnetic resonance frequency with the peak magnetic loss is decreased sensitively with the substitution of Ti and Co, which is well consistent with ferromagnetic resonance theory. Theoretical estimation of matching frequency and matching thickness for zero wave reflection is made using the solution map of impedance matching. A wide bandwidth of microwave absorption is predicted in the composite samples containing the ferrite powders of x = 0.5 in Ka-band frequencies.