Microwave magnetic and absorption properties of M-type ferrite BaCoxTixFe12−2xO19 in the Ka band

• The frequency dependence of complex permeability, permittivity and microwave absorption of BaCoxTixFe12−2xO19 have been studied in the Ka band.
• The c-axis anisotropy of BaCoxTixFe12−2xO19 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 BaCoxTixFe12−2xO19 is effectively broadened compared with other ferrites.

In this study, microwave magnetic and absorption properties were investigated for BaCoxTixFe12−2xO19 (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 BaCoxTixFe12−2xO19 decreases with the substitution, resulting in the decrease of coercivity. The frequency dependence of complex permeability, permittivity and microwave absorption of BaCoxTixFe12−2xO19 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 BaCoxTixFe12−2xO19 is effectively broadened compared with other ferrites. Therefore, BaCoxTixFe12−2xO19 may be a good candidate for electromagnetic materials with low reflectivity in the Ka band.