Tunable microwave absorption in CoAl substituted M-type BaSr hexagonal ferrite

Highlights: • Microwave absorption increases with doping of Co-Al ions in Ba-Sr hexaferrites, x = 0.2 owes -40.4 dB at 11.72 GHz & 1.4 mm • x = 0.2 has -10 dB & -20 dB bandwidth of 3.27 & 1.09 GHz at 1.5 & 1.4 mm, x = 1.0 owes -20 dB bandwidth of 170 MHz at 1.7 mm • The observed reflection loss peaks govern quarter wavelength and/or impedance matching mechanism • The frequency of microwave absorption, bandwidth can be tuned by varying thickness, doping and impedance matching M-type hexagonal ferrites with chemical composition Ba_0.5Sr_0.5Co_xAl_xFe_12-2xO₁₉ (x = 0.0, 0.2, 0.4, 0.6, 0.8 and 1.0) have been synthesized using a standard ceramic method. The electromagnetic or microwave parameters have been measured in the frequency range of 8.2 to 12.4 GHz using a vector network analyzer. The microwave absorption or reflection loss (RL) of different compositions has been evaluated comprehensively as a function of frequency, thickness and substitution Co²⁺ and Al³⁺ ions. The frequency dependence of microwave absorption, accompanied by the observed RL peaks in compositions, is governed by the quarter wavelength and/or impedance matching mechanisms. It was observed that composition x = 0.2 possesses highest RL peak of − 40.4 and − 39.7 dB at 11.72 and 10.63 GHz with thickness of 1.4 and 1.5 mm respectively. It also exhibits − 10 dB wideband absorption bandwidth of 3.27 GHz at 1.5 mm and − 20 dB absorption bandwidth of 1.09 GHz at 1.4 mm. Composition x = 1.0 owes − 20 dB narrowband absorption bandwidth of 170 MHz at 1.7 mm. The microwave absorption can be tuned by varying frequency, thickness and substitution of Co²⁺ and Al³⁺ ions. The large RL suggests that the compositions could be a potential candidate for microwave absorbing materials.