Ni-Ag alloy nanoparticles with various molar ratios were synthesized and embedded in the epoxy for the investigation of electromagnetic wave absorption properties in 2-40 GHz. The reflection loss measurement indicated Ni nanoparticles had a significant absorption in 18-40 GHz while no significant absorption was observed in the whole frequency range examined for Ag nanoparticles. Ni1Ag1 nanoparticles exhibited a significant absorption as Ni nanoparticles did, but the absorption frequency range shifted from 18-40 to 2-18 GHz. Interestingly and notably, both the Ni3Ag1 and Ni1Ag3 nanoparticles showed dual-frequency absorption in 2-18 and 18-40 GHz. It was suggested that the Ni- and Ag-rich micro-domains might be formed within the Ni3Ag1 and Ni1Ag3 nanoparticles, leading to the appearance of the second absorption due to the lags of polarization at the interfaces as the frequency was varied. The composition-related microstructure also affected the permittivity and permeability more significantly than the composition itself.
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