CoNi Nanoparticles with Different Compositions Using a Polyol Method for a Microwave Absorber in High-Frequency Bands

Abstract: Microwave absorbers are utilized to reduce electromagnetic interference, which causes device malfunctioning. A superior microwave absorber exhibits a high reflection loss value, high attenuation constant (α), good impedance matching ratio (Z = Z_in/Z₀), low thickness, and wide bandwidth (below − 10 dB). The CoNi alloy has been considered a candidate for microwave absorber applications owing to its high magnetization, low coercivity, and high magnetic loss. The composition of CoNi nanoparticles can be easily modified by adjusting the [Co]/[Ni] molar concentration ratio at a constant temperature, whose synthesis requires only 0.5 h. This study analyzes the microwave absorption properties of differently composed CoNi nanoparticles in the GHz band. Five distinct CoNi nanoparticles (Co₈₀Ni₂₀, Co₇₂Ni₂₈, Co₇₀Ni₃₀, Co₆₆Ni₃₄, and Co₅₂Ni₄₈) were prepared using the polyol method. The Ni content considerably altered the complex permittivity among other electromagnetic parameters. A 1.6 mm thick microwave absorber comprising 65 wt% Co₈₀Ni₂₀ and 35 wt% polyurethane resin exhibited a reasonable reflection loss of − 49.3 dB at 14.2 GHz, which was calculated using transmission line theory, and a wide bandwidth of 6 GHz. This could be attributed to the optimized electromagnetic parameters, interfacial polarization, attenuation constant, and magnetic loss. Graphical Abstract: [Figure not available: see fulltext.]