Tunable Twin Matching Frequency (fm1/fm2) Behavior of Ni1-xZnxFe2O4/NBR Composites over 2-12.4 GHz: A Strategic Material System for Stealth Applications

The gel to carbonate precipitate route has been used for the synthesis of Ni-1-xZnxFe2O4 (x = 0, 0.25, 0.5 and 0.75) bulk inverse spinel ferrite powder samples. The optimal zinc (50%) substitution has shown the maximum saturation magnetic moment and resulted into the maximum magnetic loss tangent (tan delta(m)) > -1.2 over the entire 2-10 GHz frequency range with an optimum value similar to-1.75 at 6 GHz. Ni0.5Zn0.5Fe2O4-Acrylo-Nitrile Butadiene Rubber (NBR) composite samples are prepared at different weight percentage (wt%) of ferrite loading fractions in rubber for microwave absorption evaluation. The 80 wt% loaded Ni0.5Zn0.5Fe2O4/NBR composite (FMAR80) sample has shown two reflection loss (RL) peaks at 5 and 10 GHz. Interestingly, a single peak at 10 GHz for 3.25 mm thickness, can be scaled down to 5 GHz by increasing the thickness up to 4.6 mm. The onset of such twin matching frequencies in FMAR80 composite sample is attributed to the spin resonance relaxation at similar to 5 GHz (f(m1)) and destructive interference lambda m/4 matched thickness near similar to 10 GHz (f(m2)) in these composite systems. These studies suggest the potential of tuning the twin frequencies in Ni0.5Zn0.5Fe2O4/NBR composite samples for possible microwave absorption applications.