Development of electroless (Ni-P)/BaNi0.4Ti0.4Fe11.2O19 nanocomposite powder for enhanced microwave absorption

Ni-, Ti-substituted nanocrystalline M-type barium hexaferrite powder (BaNixTixFe12−2xO19 (x = 0.4) of size ∼10 nm) was coated with Ni-P by electroless (EL) coating technique to form EL Ni-P/BaNi0.4Ti0.4Fe11.2O19, a radar absorbing material (RAM) nanocomposite powder. Under TEM, the particle size of RAM powders before and after Ni-P coating were found to be in the range of 10–15 nm and 15–25 nm respectively. A uniform layer of 5–10 nm thick coating is deposited due to the controlled growth of EL Ni-P nanoglobules onto the powder. A growth mechanism was proposed to understand the deposition of EL Ni-P layer onto the RAM powder. The reflection loss (RL) of the EL (Ni-P)/RAM nanocomposite powder in Ku band (12.4 −18 GHz) was evidently enhanced to −28.70 dB, as compared to the EL Ni-P nanoglobules (−16.20 dB) and nanocrystalline RAM powder (−24.20 dB). After annealing at 400 °C for 4 h, the RL and bandwidth of EL (Ni-P)/RAM nanocomposite powder was further improved from −24.20 to −35.90 dB and 1.50 to 4.00 GHz respectively. The RL enhancement mechanism was explained on the basis of VSM study (hysteresis loops) and electromagnetic theory.