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Microwave-absorbing samples were fabricated using carbon black powder, super-paramagnetic Zn0.8Ni0.2Fe2O4 nanoparticles dispersed in a SiO2 matrix, epoxy resin, and hardener. The paint was then coated onto a steel substrate. The effects of super-paramagnetic Zn0.8Ni0.2Fe2O4 nanoparticles content (0–1.75 wt%) and different coating thickness (1–2.5 mm) on microwave absorption ability in the X-band frequency range (8–12 GHz) have been studied. The results showed that paint sample containing only carbon black (20 wt%) and epoxy resin (80 wt%) expressed low microwave absorption ability at 10 GHz centered frequency (≈ 67% absorption percentage). The super-paramagnetic Zn0.8Ni0.2Fe2O4 nanoparticles strongly affected the microwave-absorbing ability. A sample of 1.5 wt% super-paramagnetic Zn0.8Ni0.2Fe2O4 nanoparticles content exhibited highest microwave absorption at 10 GHz centered frequency (≈ 99% power attenuation). Higher coating thicknesses (1–2.5 mm) led to greater microwave absorption and reached a very high absorption of 2 mm thickness (≈ 99% absorption percentage at 10 GHz centered frequency). [ABSTRACT FROM AUTHOR]