[en] In this study, microwave magnetic and absorption properties were investigated for BaCo_xTi_xFe_12−2xO₁₉ (x=0.3, 0.4 and 0.5). M-type barium ferrite can be used as high frequency absorber by Co–Ti substitution because of the strong uniaxial anisotropy and high saturated magnetization. The X-ray diffraction and magnetic hysteresis loops of the samples show that the c-axis anisotropy of BaCo_xTi_xFe_12−2xO₁₉ decreases with the substitution, resulting in the decrease of coercivity. The frequency dependence of complex permeability, permittivity and microwave absorption of BaCo_xTi_xFe_12−2xO₁₉ has been studied in the Ka band (26.5–40 GHz), respectively. The results show that the natural resonance frequency decreases with the substitution. The complex permeability increases as the sintering temperature increases in the range from 1280 °C to 1310 °C with 10 °C as a step. The imaginary part of permeability value obtained here is the highest value among the reported ferrite millimeter wave absorbers in the Ka band. The microwave absorption bandwidth at −10 dB of BaCo_xTi_xFe_12−2xO₁₉ is effectively broadened compared with other ferrites. Therefore, BaCo_xTi_xFe_12−2xO₁₉ may be a good candidate for electromagnetic materials with low reflectivity in the Ka band. - Highlights: • The frequency dependence of complex permeability, permittivity and microwave absorption of BaCo_xTi_xFe_12−2xO₁₉ have been studied in the Ka band. • The c-axis anisotropy of BaCo_xTi_xFe_12−2xO₁₉ decreases with Co–Ti substitution, resulting in the decrease of coercivity. • The natural resonance frequency decreases with Co–Ti substitution in the Ka band. • The microwave absorption bandwidth at −10 dB of BaCo_xTi_xFe_12−2xO₁₉ is effectively broadened compared with other ferrites