Tunable microwave absorption in Co-Al substituted M-type Ba-Sr hexagonal ferrite

M-type hexagonal ferrites with chemical composition Ba(0.5)Sr(0.5)Co(x)Al(x)Fe(12-2)xO(19) (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 82 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 RI, 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 wide band absorption bandwidth of 327 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. (C) 2016 Elsevier Ltd. All rights reserved.