Tunable Twin Matching Frequency (f_m1/f_m2) Behavior of Ni_1-xZn_xFe₂O₄/NBR Composites over 2-12.4 GHz: A Strategic...

The gel to carbonate precipitate route has been used for the synthesis of Ni_1-xZn_xFe₂O₄ (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 (tanδ_m) > -1.2 over the entire 2-10 GHz frequency range with an optimum value ~-1.75 at 6 GHz. Ni_0.5Zn_0.5Fe₂O₄- 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 Ni_0.5Zn_0.5Fe₂O₄/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 ~5 GHz (f_m1) and destructive interference at λ_m/4 matched thickness near ~10 GHz (f_m2) in these composite systems. These studies suggest the potential of tuning the twin frequencies in Ni_0.5Zn_0.5Fe₂O₄/NBR composite samples for possible microwave absorption applications.