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

Abstract

M-type hexagonal ferrites with chemical composition Ba0.5Sr0.5CoxAlxFe12-2xO19 (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 12.4GHz 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 −39.7dB at 11.72 and 10.63GHz with thickness of 1.4 and 1.5mm respectively. It also exhibits −10dB wideband absorption bandwidth of 3.27GHz at 1.5mm and −20dB absorption bandwidth of 1.09GHz at 1.4mm. Composition x=1.0 owes −20dB narrowband absorption bandwidth of 170MHz at 1.7mm. 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.